In 3D printing, understanding the optimal temperature for each filament is a must for achieving the best results. Different materials respond differently to heat, which is why it’s important to know the ideal temperature settings for every filament you work with. While most printers come with preset configurations, they aren’t always perfect. If the preset is off, it can lead to printing issues, making it crucial to adjust temperatures correctly.
By the end of this article, you’ll have a clear understanding of the ideal temperature ranges for various filaments and the maximum heat they can safely withstand.
Temperature plays a critical role in determining the success of the 3D printing process. It affects not only the reactivity of materials, like resin, but also the energy required to cure or solidify them. Hot resin becomes less viscous and more reactive compared to its cold counterpart, allowing it to be cured faster and with less energy. This is particularly important in environments with variable ambient temperatures since they directly impact the exposure time required for optimal results.
In terms of print quality, temperature governs material behavior, adhesion between layers, and the overall structural integrity of the final product. Proper temperature range control ensures that the filament or resin adheres properly, preventing issues like warping or layer separation. When the temperature is too low, it can lead to weak bonds between layers, while too high a temperature might result in over-extrusion and loss of detail. Temperature consistency is essential for maintaining print quality and material properties throughout the printing process.
Temperature variations can significantly impact both the aesthetic and mechanical qualities of 3D prints. Higher printing temperatures tend to produce parts with a smooth, glossy finish, while lower temperatures yield matte or satin textures. This difference in surface finish can also influence the perception of color, with gloss enhancing vibrancy and matte finishes toning down brightness. The choice of finish often depends on the material flow and the desired appearance of the final product.
Beyond aesthetics, temperature also affects the strength of the printed part. Higher temperatures improve adhesion between layers, reducing the risk of layer separation. However, pushing the temperature too high can lead to issues such as stringing, where fine threads of material stretch between different parts of the print. At the same time, excessive heat can also cause heat creep, where heat moves beyond the nozzle into cooler parts of the printer, affecting extrusion and potentially clogging the printer. Maintaining the right balance ensures both the desired finish and mechanical strength of the print.
There is no single “right” temperature for 3D printing. The optimal printing temperature can vary depending on the filament type, the specific 3D printer, and the desired properties of the final print. For example, a temperature that works well for achieving a smooth surface finish may not be the best for maximizing the part’s strength or durability.
Each filament has its own temperature range, within which the ideal settings must be chosen based on the final print requirements. Whether you aim for better print quality or mechanical resistance, understanding the material’s characteristics is key to selecting the most appropriate printing temperature for your project.
When it comes to 3D printing, each filament type has specific temperature requirements for both the nozzle and bed. These temperature settings can directly affect the quality of your prints, as well as how well the material adheres to the print bed. Understanding the recommended bed temperature ranges for each filament helps avoid common issues such as poor adhesion, warping, or layer separation. Below, we’ll look at the best printing temperatures for popular filaments, starting with PLA.
PLA is the most widely used filament in 3D printing, known for its ease of use, glass transition temperature, and flexibility under varying printing conditions. It is particularly suitable for beginners due to its forgiving nature. The recommended nozzle temperature for PLA ranges from 200°C to 220°C, while the bed temperature should be between 50°C and 60°C. Proper cooling is also essential for achieving the best print quality with PLA.
If the nozzle temperature is too high, the printing PLA can over-extrude, leading to issues such as stringing or blobs forming on the surface of the print. On the other hand, printing at too low a temperature can result in poor layer bonding, which affects the overall strength of the printed part.
ABS is a durable filament but more challenging to print compared to others like PLA. It is sensitive to rapid cooling, which can cause warping or shrinkage. Therefore, ABS requires an enclosed 3D printer to cool the print slowly and evenly. The cooling fans should generally be turned off to prevent temperature fluctuations that might affect the print’s structural integrity.
For ABS, the recommended nozzle temperature ranges between 210°C and 250°C, while the bed temperature should be maintained between 80°C and 110°C. If the temperature is too high, the material can over-extrude, resulting in poor print quality and surface imperfections. Printing at too low a temperature can cause inadequate layer adhesion, leading to cracks or part failure.
PETG is a versatile material that combines the ease of printing seen with PLA and the strength of ABS. It requires a stable temperature and a print bed with good adhesion properties, such as a layer of glue or blue painter’s tape, to ensure the filament sticks properly. PETG’s ideal nozzle temperature ranges from 220°C to 250°C, and the bed temperature should be set between 50°C and 80°C.
If the nozzle temperature is set too high when printing PETG, the material may become stringy and result in over-extrusion, which affects the print’s accuracy and finish. Conversely, too low a temperature can lead to under-extrusion and weak layer bonding, which can make the part prone to failure.
Nylon is a strong and durable filament often used for parts requiring flexibility and resistance to wear. However, it is a challenging material to work with due to its high printing temperatures and hygroscopic nature, meaning it absorbs moisture easily. Before printing, it’s essential to dry the filament thoroughly, as moisture can significantly degrade the print quality, causing bubbles or stringing. Additionally, Nylon prints best with cooling fans turned off to ensure proper adhesion between layers.
The recommended nozzle temperature for Nylon ranges from 240°C to 270°C, while the bed temperature should be set between 50°C and 70°C. When printed at too high a temperature, Nylon can suffer from stringing and excessive oozing, making the print messy and less precise. If the temperature is too low, however, the layers may not bond well, leading to weak parts that are prone to breakage.
TPU is a flexible filament ideal for creating parts that need to withstand stress and impacts, such as cases or custom grips. Its flexibility makes it more challenging to print than rigid materials, as it tends to stretch and bend during extrusion, causing potential print failures. To prevent issues like tangling or misfeeds, TPU requires a slow printing speed and a filament path that keeps it confined and controlled.
For TPU, the nozzle temperature should be set between 210°C and 230°C, with a bed temperature of 30°C to 60°C. If printed at too high a temperature, TPU can over-extrude, causing blobs and strings on the surface of the print. If the temperature is too low, the filament may not extrude properly, leading to under-extrusion and weak bonding between layers.
PET is a strong, durable filament that is commonly used for applications that require chemical resistance and food-safe prints. It requires high nozzle temperatures to properly melt and bond between layers. The ideal nozzle temperature for PET ranges from 220°C to 260°C, while the bed temperature should be between 70°C and 100°C.
When printing PET, a nozzle temperature that is too high can cause over-extrusion, resulting in blobs and an uneven surface. Conversely, a lower nozzle temperature can cause under-extrusion, leading to weak prints and layer separation. Ensuring a heated bed with good adhesion is essential to prevent warping, and adding an adhesive like a glue stick or blue tape to the bed may improve adhesion.
Polycarbonate is known for its strength and heat resistance, making it a popular choice for high-performance applications. However, printing with PC is challenging due to its high temperature requirements and tendency to warp if not handled correctly. The recommended nozzle temperature for PC is between 260°C and 310°C, with a bed temperature of 90°C to 120°C.
If the nozzle temperature is too high, PC can become stringy and lead to inconsistent extrusion. On the other hand, printing at too low a temperature can result in poor layer adhesion and brittle parts. To achieve the best results with PC, an enclosed printer is recommended to maintain a stable environment and prevent warping.
PVA is a water-soluble filament mainly used as a support material for complex prints. It works best when paired with dual extrusion printers. The optimal nozzle temperature for PVA is between 180°C to 220°C, with a bed temperature range of 45°C to 60°C. Proper temperature control is crucial to avoid issues like poor adhesion and print failure.
When printing with PVA, maintaining a low temperature helps prevent the material from burning or oozing excessively, which can cause stringing and affect print quality. On the other hand, printing at too low of a temperature can lead to under-extrusion, resulting in weak supports and poor layer adhesion. Because PVA is highly hygroscopic, keeping it in a dry, cool environment is essential to maintain its printability and performance.
HIPS is a versatile material often used for its strength and impact resistance, as well as a dissolvable support filament when paired with ABS. For optimal printing, the nozzle temperature should range from 230°C to 250°C, and the heated bed should be set between 90°C to 110°C. Achieving these temperature settings ensures good layer adhesion and minimizes the risk of warping.
Printing at too high of a temperature can lead to over-extrusion, causing surface irregularities, while printing at too low of a temperature may result in brittle parts and gaps between layers. To avoid print issues, use an enclosure for HIPS to maintain a stable environment, which helps in preventing warping due to drafts or sudden temperature changes during printing.
POM, also known as acetal, is a strong and durable material known for its low friction and high rigidity. Printing with POM requires specific temperature management to achieve the best results. The recommended nozzle temperature is between 210°C to 230°C, and the bed temperature should range from 100°C to 130°C.
Too high a temperature may lead to over-extrusion, causing surface defects and weakened prints. Conversely, printing at too low of a temperature can result in poor layer adhesion and print failures. Additionally, since POM has a tendency to warp, using a heated bed is essential, along with an enclosure to maintain ambient temperature stability and prevent warping during the cooling process.
Carbon fiber reinforced filaments offer enhanced strength and stiffness, making them popular for high-performance applications. These filaments require higher printing temperatures due to the carbon fiber content. The recommended nozzle temperature falls between 200°C and 260°C, while the bed temperature should range from 50°C to 100°C.
When printing at too high a temperature, you might encounter issues like over-extrusion and stringing, which can negatively impact the surface finish. At lower temperatures, under-extrusion and poor adhesion between layers can result in weak prints. To avoid clogging, it is recommended to use a hardened nozzle, as carbon fiber is abrasive and can wear out standard nozzles quickly.
Temperature control is essential for ensuring high-quality results across various 3D printing technologies. Each printing process has unique requirements based on the materials used and the technology involved. Here’s how temperature impacts the most common 3D printing technologies, including fused filament fabrication (FFF) and digital light processing (DLP).
Temperature has a significant impact on various parts of a 3D printer. Components like the extruder, nozzle, and print bed all rely on precise temperature control to ensure high-quality prints. When temperatures fluctuate or exceed the recommended ranges, the printer’s performance can be negatively affected, leading to issues like warping, clogging, or layer separation. Proper temperature management ensures that the printer maintains consistent material flow and that the printed object adheres correctly to the bed while retaining the desired
The extruder is responsible for feeding the filament into the hotend, where it melts and is extruded through the nozzle. Maintaining the right 3D printing temperature here is essential. If the temperature is too high, the filament can become too fluid, leading to over-extrusion or oozing. On the other hand, if the temperature is too low, the filament may not melt sufficiently, causing under-extrusion or uneven flow. To avoid these issues, the extruder must remain within the ideal temperature range that matches the filament being used, ensuring smooth and
The nozzle is where the melted filament is extruded and deposited onto the print bed. Nozzle temperature is a crucial factor that directly affects material flow and print quality. If the nozzle operates at too high a temperature, you may experience issues like stringing, blobs, and over-extrusion. Conversely, a nozzle that is too cool can lead to clogs and incomplete layers, especially when working with more complex designs. Achieving the correct temperature range for the nozzle helps prevent these problems, ensuring that the material flows smoothly and adheres correctly to the previous layers, maintaining the structural integrity of the printed object.
The heated bed is crucial for ensuring that the first layer of filament sticks properly to the build platform. A well-regulated bed temperature helps avoid warping and detachment during printing. If the bed is too cold, the print may fail to adhere properly, leading to warping or detachment from the platform. On the other hand, if the bed is too hot, the filament may become too soft, resulting in a warped or distorted base that is difficult to remove from the bed. Therefore, striking the right balance is necessary to maintain the print’s integrity throughout the process.
The bed temperature is crucial for adhesion and preventing warping. Generally, different materials require different bed temperatures. For instance, PLA typically requires a bed temperature between 50°C to 60°C, while ABS often needs a higher range between 80°C to 110°C. Adjusting the bed temperature based on material type and environmental factors, such as room temperature and airflow, helps avoid print failures. The heated bed should provide even warmth across the surface to ensure consistent adhesion throughout the printing process.
A hotter bed is not always better. The ideal bed temperature depends on the material being printed. Higher temperatures can improve adhesion for filaments like ABS, but too much heat might cause issues like softening or warping in materials like PLA. The key is to adjust the bed temperature to match the material’s needs and maintain the best print quality.
If the bed temperature is too high, the filament may become overly soft, leading to problems like over-adhesion. This can make it difficult to remove the print from the bed and may cause warping or deformation in the base layer. Additionally, excessive heat can also result in uneven cooling, which may affect the overall print quality and cause surface defects.
The hotend is responsible for heating and melting the filament. Maintaining the correct temperature is essential for a smooth extrusion. If the hotend is too hot, over-extrusion and stringing may occur. Too low a temperature can result in under-extrusion, causing incomplete layers and weak prints.
The print chamber or enclosure helps regulate the ambient temperature around the print. It prevents drafts or rapid cooling, which can lead to warping, especially with materials like ABS. Keeping a stable temperature inside the enclosure ensures better adhesion and layer bonding during the printing process.
Cooling fans manage the temperature of the freshly extruded filament, helping it solidify in place. If the fans cool too quickly, it can cause layer separation or cracking. Inadequate cooling may result in poor print quality, especially on overhangs and bridges. Balancing fan speed is crucial for print accuracy.
Stepper motors control the movement of the print head and build platform. If the temperature gets too high, the motors may overheat, causing missed steps or decreased precision. Proper ventilation and cooling are necessary to maintain steady performance during long prints.
The power supply provides energy to all the printer’s components. High temperatures can cause it to overheat, potentially leading to power fluctuations or failures. Keeping the environment cool and ensuring adequate airflow around the power supply helps avoid issues.
The control board manages the printer’s operations, including temperature settings. Excessive heat can affect its performance, leading to erratic temperature regulation or communication errors. Cooling fans and proper enclosure temperature management are essential for keeping the control board functioning reliably.
Filaments are sensitive to temperature and humidity. If stored in a hot or humid environment, they may absorb moisture, causing print quality to degrade. Keeping filaments in a cool, dry space is essential for maintaining their material properties and preventing print failures.
The build plate, also known as the print bed, must maintain an ideal temperature range to ensure proper adhesion of the first layer. A build plate that’s too cool can cause warping, while an excessively hot plate may result in soft, hard-to-remove prints. Proper temperature balance is critical for high-quality prints.
Choosing the right printing temperature is essential for achieving optimal print quality. It affects material flow, layer adhesion, and overall success. By carefully following the steps below, you can fine-tune your printer’s settings for the best results.
Proper temperature settings are crucial for successful 3D printing. When the temperature is either too high or too low, it can lead to a variety of issues, negatively affecting print quality and structural integrity. Below, we explore the problems caused by excessive printing temperatures and their effects on the printing process.
When the printing temperature is set too high, it can cause several problems. The following are some of the most common issues:
When the printing temperature is set too low, various issues can arise. Here are some common problems associated with low temperatures:
Temperature and print speed are closely related in 3D printing. They work together to control the material flow, ensuring the filament is deposited correctly to maintain print quality. If you adjust one without considering the other, you may experience issues like poor adhesion, stringing, or incomplete extrusion.
When printing at higher speeds, the material needs to flow quickly, so a higher temperature is required to keep it in a molten state. On the other hand, lower speeds allow you to reduce the temperature without compromising the print. Finding the right balance between print speed and temperature is key to achieving the best results for different materials and models.
Calibrating your 3D printer for optimal temperature settings is essential to maintain print quality. The calibration process involves testing different temperatures to determine the ideal range for your filament and print setup. Regular calibration ensures that your prints remain precise and free from common issues like under-extrusion or stringing.
Optimizing the printing temperature is key to achieving the desired strength, flexibility, and appearance in your 3D prints. Different materials have different temperature ranges, and adjusting these can help fine-tune the final product based on what you’re looking to accomplish.
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The surface finish of your print can be significantly affected by how well you manage the printing temperature. Here are some helpful tips to achieve the finish you want:
The ideal room temperature for 3D printing, especially when using PLA filament, ranges between 20°C and 25°C (68°F to 77°F). This range creates a stable environment, reducing the likelihood of warping and helping the first layer adhere better to the print bed. Ambient temperature plays a crucial role in maintaining print quality. Too cold or too hot of a room can affect layer bonding, print accuracy, and lead to potential failures in the printing process.
Printing in a cold room is generally not advisable. Lower ambient temperatures can lead to problems such as poor filament flow and inadequate adhesion. As the temperature drops, the plastic cools too quickly, preventing proper bonding between layers, which can result in delamination or warping. Additionally, cold rooms can cause issues with the heated bed, reducing its ability to maintain a stable temperature for the print. If you must print in a colder environment, using an enclosure to trap heat can help maintain a consistent printing temperature.
Printing in a hot room can cause several challenges. High ambient temperatures can lead to heat creep, where heat from the hotend travels upward, softening the filament too early and causing jams or clogs. Excessive heat can also cause prints to warp, especially if the cooling fan is not performing efficiently. To manage this, it’s essential to monitor the temperature inside the enclosure and adjust the fan speed accordingly to avoid overheating the filament. Maintaining proper airflow in the room can help mitigate these issues and result in better print quality.
When working with high-temperature 3D printing, safety is critical. Here are some important precautions to follow:
The ideal storage temperature for 3D printers is typically between 10°C and 30°C (50°F to 86°F). This range helps prevent condensation and other environmental factors that can damage the printer’s electronics and components. High humidity or extreme cold can affect the machine’s performance, while storing it in an environment with moderate temperatures can ensure its longevity. Proper storage also helps maintain optimal print quality by protecting the internal parts from unnecessary stress caused by temperature fluctuations.
To achieve the best quality in 3D printing, precise temperature control is key. Understanding how temperature affects the printing process unlocks the potential for consistently high-quality prints while avoiding common problems like warping, heat creep, and under-extrusion. Proper temperature settings not only enhance surface finishes but also improve the structural integrity of your prints.
By regularly adjusting and fine-tuning temperatures based on the material and environmental conditions, you’ll see more reliable and optimal results with every print. Continuous experimentation is the path to perfecting your 3D printing projects.
Yes, ambient temperature directly impacts 3D printing outcomes. A room that is too cold can cause uneven cooling, resulting in warping or poor layer adhesion. If the air is too warm, heat creep and poor print quality can occur due to excessive softening of the filament before extrusion. Maintaining an ideal room temperature between 68°F and 77°F ensures consistent print quality. For higher temperature applications or materials like ABS, an enclosed environment or heated bed can mitigate issues caused by fluctuating air temperatures.
High-temperature superconductivity (high-Tc or HTS) is superconductivity in materials with a critical temperature (the temperature below which the material behaves as a superconductor) above 77 K (−196.2 °C; −321.1 °F), the boiling point of liquid nitrogen.[1] They are "high-temperature" only relative to previously known superconductors, which function only closer to absolute zero. The first high-temperature superconductor was discovered in by IBM researchers Georg Bednorz and K. Alex Müller.[2][3] Although the critical temperature is around 35.1 K (−238.1 °C; −396.5 °F), this material was modified by Ching-Wu Chu to make the first high-temperature superconductor with critical temperature 93 K (−180.2 °C; −292.3 °F).[4] Bednorz and Müller were awarded the Nobel Prize in Physics in "for their important break-through in the discovery of superconductivity in ceramic materials".[5] Most high-Tc materials are type-II superconductors.
The major advantage of high-temperature superconductors is that they can be cooled using liquid nitrogen,[2] in contrast to previously known superconductors, which require expensive and hard-to-handle coolants, primarily liquid helium. A second advantage of high-Tc materials is they retain their superconductivity in higher magnetic fields than previous materials. This is important when constructing superconducting magnets, a primary application of high-Tc materials.
The majority of high-temperature superconductors are ceramics, rather than the previously known metallic materials. Ceramic superconductors are suitable for some practical uses but encounter manufacturing issues. For example, most ceramics are brittle, which complicates wire fabrication.[6]
The main class of high-temperature superconductors is copper oxides combined with other metals, especially the rare-earth barium copper oxides (REBCOs) such as yttrium barium copper oxide (YBCO). The second class of high-temperature superconductors in the practical classification is the iron-based compounds.[7][8] Magnesium diboride is sometimes included in high-temperature superconductors: It is relatively simple to manufacture, but it superconducts only below 39 K (−234.2 °C), which makes it unsuitable for liquid nitrogen cooling.
Superconductivity was discovered by Kamerlingh Onnes in , in a metal solid. Ever since, researchers have attempted to create superconductivity at higher temperatures[9] with the goal of finding a room-temperature superconductor.[10] By the late s, superconductivity was observed in several metallic compounds (in particular Nb-based, such as NbTi, Nb3Sn, and Nb3Ge) at temperatures that were much higher than those for elemental metals and which could even exceed 20 K (−253.2 °C).
In , at the IBM research lab near Zürich in Switzerland, Bednorz and Müller were looking for superconductivity in a new class of ceramics: the copper oxides, or cuprates. In that year, Bednorz and Müller discovered superconductivity in lanthanum barium copper oxide (LBCO), a lanthanum-based cuprate perovskite material, which had a transition temperature of 35 K (Nobel Prize in Physics, ).[11] It was soon found that replacing the lanthanum with yttrium (i.e., making YBCO) raised the critical temperature above 90 K.[12] Their results were soon confirmed[13] by many groups.[14]
In , Philip W. Anderson gave the first theoretical description of these materials, based on the resonating valence bond (RVB) theory,[15] but a full understanding of these materials is still developing today. These superconductors are now known to possess a d-wave[clarification needed] pair symmetry. The first proposal that high-temperature cuprate superconductivity involves d-wave pairing was made in by N. E. Bickers, Douglas James Scalapino and R. T. Scalettar,[16] followed by three subsequent theories in by Masahiko Inui, Sebastian Doniach, Peter J. Hirschfeld and Andrei E. Ruckenstein,[17] using spin-fluctuation theory, and by Claudius Gros, Didier Poilblanc, Maurice T. Rice and FC. Zhang,[18] and by Gabriel Kotliar and Jialin Liu identifying d-wave pairing as a natural consequence of the RVB theory.[19] The confirmation of the d-wave nature of the cuprate superconductors was made by a variety of experiments, including the direct observation of the d-wave nodes in the excitation spectrum through angle resolved photoemission spectroscopy (ARPES), the observation of a half-integer flux in tunneling experiments, and indirectly from the temperature dependence of the penetration depth, specific heat and thermal conductivity.
Until the cuprates were thought be the only true high temperature superconductors. In that year MgB2 with Tc of 39K was discovered by Akimitsu and colleagues. This was followed in by Hosono and coworkers with iron-based layered oxypnictide compound with Tc of 56K.[20] These temperature are below the cuprates but well above the conventional superconductors.[21]
In , evidence showing that fractional particles can happen in quasi two-dimensional magnetic materials was reported by École Polytechnique Fédérale de Lausanne (EPFL) scientists[22] lending support for Anderson's theory of high-temperature superconductivity.[23] In and , hydrogen sulfide (H
2S) at extremely high pressures (around 150 gigapascals) was first predicted and then confirmed to be a high-temperature superconductor with a transition temperature of 80 K.[24][25][26]
In , a research team from the Department of Physics, Massachusetts Institute of Technology, discovered superconductivity in bilayer graphene with one layer twisted at an angle of approximately 1.1 degrees with cooling and applying a small electric charge. Even if the experiments were not carried out in a high-temperature environment, the results are correlated less to classical but high temperature superconductors, given that no foreign atoms needed to be introduced.[27] The superconductivity effect came about as a result of electrons twisted into a vortex between the graphene layers, called "skyrmions". These act as a single particle and can pair up across the graphene's layers, leading to the basic conditions required for superconductivity.[28]
In it was discovered that lanthanum hydride (LaH
10) becomes a superconductor at 250 K under a pressure of 170 gigapascals.[29][26]
In , a room-temperature superconductor (critical temperature 288 K) made from hydrogen, carbon and sulfur under pressures of around 270 gigapascals was described in a paper in Nature.[30][31] However, in the article was retracted by the editors because the validity of background subtraction procedures had been called into question. All nine authors maintain that the raw data strongly support the main claims of the paper.[32]
In a study reported superconductivity at room temperature and ambient pressure in highly oriented pyrolytic graphite with dense arrays of nearly parallel line defects.[33]
As of ,[34] the superconductor with the highest transition temperature at ambient pressure was the cuprate of mercury, barium, and calcium, at around 133 K (−140 °C).[35] Other superconductors have higher recorded transition temperatures – for example lanthanum superhydride at 250 K (−23 °C), but these only occur at high pressure.[36]
The "high-temperature" superconductor class has had many definitions.
The label high-Tc should be reserved for materials with critical temperatures greater than the boiling point of liquid nitrogen. However, a number of materials – including the original discovery and recently discovered pnictide superconductors – have critical temperatures below 77 K (−196.2 °C) but nonetheless are commonly referred to in publications as high-Tc class.[43][44]
A substance with a critical temperature above the boiling point of liquid nitrogen, together with a high critical magnetic field and critical current density (above which superconductivity is destroyed), would greatly benefit technological applications. In magnet applications, the high critical magnetic field may prove more valuable than the high Tc itself. Some cuprates have an upper critical field of about 100 tesla. However, cuprate materials are brittle ceramics that are expensive to manufacture and not easily turned into wires or other useful shapes. Furthermore, high-temperature superconductors do not form large, continuous superconducting domains, rather clusters of microdomains within which superconductivity occurs. They are therefore unsuitable for applications requiring actual superconductive currents, such as magnets for magnetic resonance spectrometers.[45] For a solution to this (powders), see HTS wire.
There has been considerable debate regarding high-temperature superconductivity coexisting with magnetic ordering in YBCO,[46] iron-based superconductors, several ruthenocuprates and other exotic superconductors, and the search continues for other families of materials. HTS are Type-II superconductors, which allow magnetic fields to penetrate their interior in quantized units of flux, meaning that much higher magnetic fields are required to suppress superconductivity. The layered structure also gives a directional dependence to the magnetic field response.
All known high-Tc superconductors are Type-II superconductors. In contrast to Type-I superconductors, which expel all magnetic fields due to the Meissner effect, Type-II superconductors allow magnetic fields to penetrate their interior in quantized units of flux, creating "holes" or "tubes" of normal metallic regions in the superconducting bulk called vortices. Consequently, high-Tc superconductors can sustain much higher magnetic fields.
Iron-based superconductors contain layers of iron and a pnictogen – such as arsenic or phosphorus – , a chalcogen, or a crystallogen. This is currently the family with the second highest critical temperature, behind the cuprates. Interest in their superconducting properties began in with the discovery of superconductivity in LaFePO at 4 K (−269.15 °C)[49] and gained much greater attention in after the analogous material LaFeAs(O,F)[50] was found to superconduct at up to 43 K (−230.2 °C) under pressure.[51] The highest critical temperatures in the iron-based superconductor family exist in thin films of FeSe,[52][53][54] where a critical temperature in excess of 100 K (−173 °C) was reported in .[55]
Since the original discoveries several families of iron-based superconductors have emerged:
Most undoped iron-based superconductors show a tetragonal-orthorhombic structural phase transition followed at lower temperature by magnetic ordering, similar to the cuprate superconductors.[66] However, they are poor metals rather than Mott insulators and have five bands at the Fermi surface rather than one.[48] The phase diagram emerging as the iron-arsenide layers are doped is remarkably similar, with the superconducting phase close to or overlapping the magnetic phase. Strong evidence that the Tc value varies with the As–Fe–As bond angles has already emerged and shows that the optimal Tc value is obtained with undistorted FeAs4 tetrahedra.[67] The symmetry of the pairing wavefunction is still widely debated, but an extended s-wave scenario is currently favoured.
Magnesium diboride is occasionally referred to as a high-temperature superconductor[68] because its Tc value of 39 K (−234.2 °C) is above that historically expected for BCS superconductors. However, it is more generally regarded as the highest Tc conventional superconductor, the increased Tc resulting from two separate bands being present at the Fermi level.
In Hebard et al. discovered Fulleride superconductors,[69] where alkali-metal atoms are intercalated into C60 molecules.
In Ganin et al. demonstrated superconductivity at temperatures of up to 38 K (−235.2 °C) for Cs3C60.[70]
P-doped Graphane was proposed in to be capable of sustaining high-temperature superconductivity.[71]
On 31st of December "Global Room-Temperature Superconductivity in Graphite" was published in the journal "Advanced Quantum Technologies" claiming to demonstrate superconductivity at room temperature and ambient pressure in Highly oriented pyrolytic graphite with dense arrays of nearly parallel line defects.[72]
In , Anisimov et al. conjectured superconductivity in nickelates, proposing nickel oxides as direct analogs to the cuprate superconductors.[73] Superconductivity in an infinite-layer nickelate, Nd0.8Sr0.2NiO2, was reported at the end of with a superconducting transition temperature between 9 and 15 K (−264.15 and −258.15 °C).[74][75] This superconducting phase is observed in oxygen-reduced thin films created by the pulsed laser deposition of Nd0.8Sr0.2NiO3 onto SrTiO3 substrates that is then reduced to Nd0.8Sr0.2NiO2 via annealing the thin films at 533–553 K (260–280 °C) in the presence of CaH2.[76] The superconducting phase is only observed in the oxygen reduced film and is not seen in oxygen reduced bulk material of the same stoichiometry, suggesting that the strain induced by the oxygen reduction of the Nd0.8Sr0.2NiO2 thin film changes the phase space to allow for superconductivity.[77] Of important is further to extract access hydrogen from the reduction with CaH2, otherwise topotactic hydrogen may prevent superconductivity. [78]
Liquid nitrogen can be produced relatively cheaply, even on-site. The higher temperatures additionally help to avoid some of the problems that arise at liquid helium temperatures, such as the formation of plugs of frozen air that can block cryogenic lines and cause unanticipated and potentially hazardous pressure buildup.[79][80]
The question of how superconductivity arises in high-temperature superconductors is one of the major unsolved problems of theoretical condensed matter physics. The mechanism that causes the electrons in these crystals to form pairs is not known. Despite intensive research and many promising leads, an explanation has so far eluded scientists. One reason for this is that the materials in question are generally very complex, multi-layered crystals (for example, BSCCO), making theoretical modelling difficult.
Improving the quality and variety of samples also gives rise to considerable research, both with the aim of improved characterisation of the physical properties of existing compounds, and synthesizing new materials, often with the hope of increasing Tc. Technological research focuses on making HTS materials in sufficient quantities to make their use economically viable [81] as well as in optimizing their properties in relation to applications.[82] Metallic hydrogen has been proposed as a room-temperature superconductor, some experimental observations have detected the occurrence of the Meissner effect.[83][84] LK-99, copper-doped lead-apatite, has also been proposed as a room-temperature superconductor.
Multiple hypotheses attempt to account for HTS.
Resonating-valence-bond theory
Spin fluctuation hypothesis[85] proposed that electron pairing in high-temperature superconductors is mediated by short-range spin waves known as paramagnons.[86][87][dubious – discuss]
Gubser, Hartnoll, Herzog, and Horowitz proposed holographic superconductivity, which uses holographic duality or AdS/CFT correspondence theory as a possible explanation of high-temperature superconductivity in certain materials.[88]
Weak coupling theory suggests superconductivity emerges from antiferromagnetic spin fluctuations in a doped system.[89] It predicts that the pairing wave function of cuprate HTS should have a dx2-y2 symmetry. Thus, determining whether the pairing wave function has d-wave symmetry is essential to test the spin fluctuation mechanism. That is, if the HTS order parameter (a pairing wave function as in Ginzburg–Landau theory) does not have d-wave symmetry, then a pairing mechanism related to spin fluctuations can be ruled out. (Similar arguments can be made for iron-based superconductors but the different material properties allow a different pairing symmetry.)
Interlayer coupling theory proposes that a layered structure consisting of BCS-type (s-wave symmetry) superconductors can explain superconductivity by itself.[90] By introducing an additional tunnelling interaction between layers, this model explained the anisotropic symmetry of the order parameter as well as the emergence of HTS.
In order to resolve this question, experiments such as photoemission spectroscopy, NMR, specific heat measurements, were conducted. The results remain ambiguous, with some reports supporting d symmetry, with others supporting s symmetry.
Such explanations assume that superconductive properties can be treated by mean-field theory. It also does not consider that in addition to the superconductive gap, the pseudogap must be explained. The cuprate layers are insulating, and the superconductors are doped with interlayer impurities to make them metallic.
The transition temperature can be maximized by varying the dopant concentration. The simplest example is La2CuO4, which consists of alternating CuO2 and LaO layers that are insulating when pure. When 8% of the La is replaced by Sr, the latter acts as a dopant, contributing holes to the CuO2 layers, and making the sample metallic. The Sr impurities also act as electronic bridges, enabling interlayer coupling. Proceeding from this picture, some theories argue that the pairing interaction is with phonons, as in conventional superconductors with Cooper pairs. While the undoped materials are antiferromagnetic, even a few percent of impurity dopants introduce a smaller pseudogap in the CuO2 planes that is also caused by phonons. The gap decreases with increasing charge carriers, and as it nears the superconductive gap, the latter reaches its maximum. The transition temperature is then argued to be due to the percolating behaviour of the carriers, which follow zig-zag percolative paths, largely in metallic domains in the CuO2 planes, until blocked by charge density wave domain walls, where they use dopant bridges to cross over to a metallic domain of an adjacent CuO2 plane. The transition temperature maxima are reached when the host lattice has weak bond-bending forces, which produce strong electron–phonon interactions at the interlayer dopants.[91]
An experiment based on flux quantization of a three-grain ring of YBa2Cu3O7 (YBCO) was proposed to test the symmetry of the order parameter in the HTS. The symmetry of the order parameter could best be probed at the junction interface as the Cooper pairs tunnel across a Josephson junction or weak link.[92] It was expected that a half-integer flux, that is, a spontaneous magnetization could only occur for a junction of d symmetry superconductors. But, even if the junction experiment is the strongest method to determine the symmetry of the HTS order parameter, the results have been ambiguous. John R. Kirtley and C. C. Tsuei thought that the ambiguous results came from the defects inside the HTS, leading them to an experiment where both clean limit (no defects) and dirty limit (maximal defects) were considered simultaneously.[93] Spontaneous magnetization was clearly observed in YBCO, which supported the d symmetry of the order parameter in YBCO. But, since YBCO is orthorhombic, it might inherently have an admixture of s symmetry. By tuning their technique, they found an admixture of s symmetry in YBCO within about 3%.[94] Also, they found a pure dx2−y2 order parameter symmetry in tetragonal Tl2Ba2CuO6.[95]
The lack of exact theoretical computations on such strongly interacting electron systems has complicated attempts to validate spin-fluctuation. However, most theoretical calculations, including phenomenological and diagrammatic approaches, converge on magnetic fluctuations as the pairing mechanism.
In a superconductor, the flow of electrons cannot be resolved into individual electrons, but instead consists of pairs of bound electrons, called Cooper pairs. In conventional superconductors, these pairs are formed when an electron moving through the material distorts the surrounding crystal lattice, which attracts another electron and forms a bound pair. This is sometimes called the "water bed" effect. Each Cooper pair requires a certain minimum energy to be displaced, and if the thermal fluctuations in the crystal lattice are smaller than this energy the pair can flow without dissipating energy. Electron flow without resistance is superconductivity.
In a high-Tc superconductor, the mechanism is extremely similar to a conventional superconductor, except that phonons play virtually no role, replaced by spin-density waves. Just as all known conventional superconductors are strong phonon systems, all known high-Tc superconductors are strong spin-density wave systems, within close vicinity of a magnetic transition to, for example, an antiferromagnet. When an electron moves in a high-Tc superconductor, its spin creates a spin-density wave around it. This spin-density wave in turn causes a nearby electron to fall into the spin depression created by the first electron (water-bed). When the system temperature is lowered, more spin density waves and Cooper pairs are created, eventually leading to superconductivity. High-Tc systems are magnetic systems due to the Coulomb interaction, creating a strong Coulomb repulsion between electrons. This repulsion prevents pairing of the Cooper pairs on the same lattice site. Instead, pairing occurs at near-neighbor lattice sites. This is the so-called d-wave pairing, where the pairing state has a node (zero) at the origin.
Examples of high-Tc cuprate superconductors include YBCO and BSCCO, which are the most known materials that achieve superconductivity above the boiling point of liquid nitrogen.
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Temperatures of most practical superconductors and coolants, at ordinary pressures Transition temperature Item Material type 195 K (−78 °C) Dry ice (Carbon dioxide) – sublimation Coolant 184 K (−89 °C) Lowest temperature recorded on Earth Coolant 110 K (−163 °C) BSCCO Cuprate superconductors 93 K (−180.2 °C) YBCO 77 K (−196.2 °C) Nitrogen – Boiling Coolant 55 K (−218.2 °C) SmFeAs(O,F) Iron-based superconductors 41 K (−232.2 °C) CeFeAs(O,F) 26 K (−247.2 °C) LaFeAs(O,F) 18 K (−255.2 °C) Nb3Sn Metallic low-temperature superconductors 3K (−270 °C) Helium – boiling Coolant 3 K (−270.15 °C) Hg (mercury: the first discovered superconductor) Metallic low-temperature superconductors