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News Article | May 16, 2017
Site: www.sciencedaily.com

University of Houston physicists have discovered a catalyst that can split water into hydrogen and oxygen, composed of easily available, low-cost materials and operating far more efficiently than previous catalysts. That would solve one of the primary hurdles remaining in using water to produce hydrogen, one of the most promising sources of clean energy. "Hydrogen is the cleanest primary energy source we have on earth," said Paul C. W. Chu, TLL Temple Chair of Science and founding director and chief scientist of the Texas Center for Superconductivity at UH. "Water could be the most abundant source of hydrogen if one could separate the hydrogen from its strong bond with oxygen in the water by using a catalyst." Chu and colleagues including physicists Zhifeng Ren and Shuo Chen, both of whom also are principal investigators with the Texas Center for Superconductivity at UH, report their discovery -- an efficient catalyst produced without the expensive precious metals most commonly used -- this week in the Proceedings of the Natural Academy of Sciences. Other researchers involved in the project include postdoctoral researchers Haiqing Zhou and Fang Yu, and graduate students Jingying Sun and Ran He. The catalyst, composed of ferrous metaphosphate grown on a conductive nickel foam platform, is far more efficient than previous catalysts, as well as less expensive to produce. "Cost-wise, it is much lower and performance-wise, much better," said Zhifeng Ren, M.D. Anderson professor of physics and lead author on the paper. The catalyst also is durable, operating more than 20 hours and 10,000 cycles in testing. "Some catalysts are outstanding but are only stable for one or two hours," Ren said. "That's no use." Although it is simple in theory, splitting water into hydrogen and oxygen is a complex process, requiring two separate reactions -- a hydrogen evolution reaction and an oxygen evolution reaction, each requiring a separate electrode. While hydrogen is the more valuable component, it can't be produced without also producing oxygen. And while efficient hydrogen catalysts are available, Ren said the lack of an inexpensive and efficient oxygen catalyst has created a bottleneck in the field. Hydrogen has a number of advantages. "Hydrogen (H ) produced from water splitting by an electrochemical process, called water electrolysis, has been considered to be a clean and sustainable energy resource to replace fossil fuels and meet the rising global energy demand, since water is both the sole starting material and byproduct when clean energy is produced by converting H back to water," the researchers wrote. And unlike solar power, wind power and other "clean" energy, hydrogen can be easily stored. Currently, most hydrogen is produced through steam methane reforming and coal gasification; those methods raise the fuel's carbon footprint despite the fact that it burns cleanly. Chen said oxygen evolution reactions often depend upon an electrocatalyst using a "noble metal" -- iridium, platinum or ruthenium. But those are expensive and not readily available. "In this work, we discovered a highly active and stable electrocatalyst based on earth-abundant elements, which even outperforms the noble metal based ones," she said. "Our discovery may lead to a more economic approach for hydrogen production from water electrolysis." Water splitting can be triggered either through electric current or through photocatalysis, using the power of the sun. Direct solar-powered water splitting is too inefficient, as water can absorb just a small portion of the light spectrum. Ideally, Ren said, solar power would be used to generate the electric power used to split water.


News Article | May 15, 2017
Site: www.eurekalert.org

University of Houston physicists have discovered a catalyst that can split water into hydrogen and oxygen, composed of easily available, low-cost materials and operating far more efficiently than previous catalysts. That would solve one of the primary hurdles remaining in using water to produce hydrogen, one of the most promising sources of clean energy. "Hydrogen is the cleanest primary energy source we have on earth," said Paul C. W. Chu, TLL Temple Chair of Science and founding director and chief scientist of the Texas Center for Superconductivity at UH. "Water could be the most abundant source of hydrogen if one could separate the hydrogen from its strong bond with oxygen in the water by using a catalyst." Chu and colleagues including physicists Zhifeng Ren and Shuo Chen, both of whom also are principal investigators with the Texas Center for Superconductivity at UH, report their discovery - an efficient catalyst produced without the expensive precious metals most commonly used -- this week in the Proceedings of the Natural Academy of Sciences. Other researchers involved in the project include postdoctoral researchers Haiqing Zhou and Fang Yu, and graduate students Jingying Sun and Ran He. The catalyst, composed of ferrous metaphosphate grown on a conductive nickel foam platform, is far more efficient than previous catalysts, as well as less expensive to produce. "Cost-wise, it is much lower and performance-wise, much better," said Zhifeng Ren, M.D. Anderson professor of physics and lead author on the paper. The catalyst also is durable, operating more than 20 hours and 10,000 cycles in testing. "Some catalysts are outstanding but are only stable for one or two hours," Ren said. "That's no use." Although it is simple in theory, splitting water into hydrogen and oxygen is a complex process, requiring two separate reactions - a hydrogen evolution reaction and an oxygen evolution reaction, each requiring a separate electrode. While hydrogen is the more valuable component, it can't be produced without also producing oxygen. And while efficient hydrogen catalysts are available, Ren said the lack of an inexpensive and efficient oxygen catalyst has created a bottleneck in the field. Hydrogen has a number of advantages. "Hydrogen (H2) produced from water splitting by an electrochemical process, called water electrolysis, has been considered to be a clean and sustainable energy resource to replace fossil fuels and meet the rising global energy demand, since water is both the sole starting material and byproduct when clean energy is produced by converting H2 back to water," the researchers wrote. And unlike solar power, wind power and other "clean" energy, hydrogen can be easily stored. Currently, most hydrogen is produced through steam methane reforming and coal gasification; those methods raise the fuel's carbon footprint despite the fact that it burns cleanly. Chen said oxygen evolution reactions often depend upon an electrocatalyst using a "noble metal" - iridium, platinum or ruthenium. But those are expensive and not readily available. "In this work, we discovered a highly active and stable electrocatalyst based on earth-abundant elements, which even outperforms the noble metal based ones," she said. "Our discovery may lead to a more economic approach for hydrogen production from water electrolysis." Water splitting can be triggered either through electric current or through photocatalysis, using the power of the sun. Direct solar-powered water splitting is too inefficient, as water can absorb just a small portion of the light spectrum. Ideally, Ren said, solar power would be used to generate the electric power used to split water.


News Article | May 15, 2017
Site: phys.org

That would solve one of the primary hurdles remaining in using water to produce hydrogen, one of the most promising sources of clean energy. "Hydrogen is the cleanest primary energy source we have on earth," said Paul C. W. Chu, TLL Temple Chair of Science and founding director and chief scientist of the Texas Center for Superconductivity at UH. "Water could be the most abundant source of hydrogen if one could separate the hydrogen from its strong bond with oxygen in the water by using a catalyst." Chu and colleagues including physicists Zhifeng Ren and Shuo Chen, both of whom also are principal investigators with the Texas Center for Superconductivity at UH, report their discovery - an efficient catalyst produced without the expensive precious metals most commonly used—this week in the Proceedings of the Natural Academy of Sciences. Other researchers involved in the project include postdoctoral researchers Haiqing Zhou and Fang Yu, and graduate students Jingying Sun and Ran He. The catalyst, composed of ferrous metaphosphate grown on a conductive nickel foam platform, is far more efficient than previous catalysts, as well as less expensive to produce. "Cost-wise, it is much lower and performance-wise, much better," said Zhifeng Ren, M.D. Anderson professor of physics and lead author on the paper. The catalyst also is durable, operating more than 20 hours and 10,000 cycles in testing. "Some catalysts are outstanding but are only stable for one or two hours," Ren said. "That's no use." Although it is simple in theory, splitting water into hydrogen and oxygen is a complex process, requiring two separate reactions - a hydrogen evolution reaction and an oxygen evolution reaction, each requiring a separate electrode. While hydrogen is the more valuable component, it can't be produced without also producing oxygen. And while efficient hydrogen catalysts are available, Ren said the lack of an inexpensive and efficient oxygen catalyst has created a bottleneck in the field. Hydrogen has a number of advantages. "Hydrogen (H2) produced from water splitting by an electrochemical process, called water electrolysis, has been considered to be a clean and sustainable energy resource to replace fossil fuels and meet the rising global energy demand, since water is both the sole starting material and byproduct when clean energy is produced by converting H2 back to water," the researchers wrote. And unlike solar power, wind power and other "clean" energy, hydrogen can be easily stored. Currently, most hydrogen is produced through steam methane reforming and coal gasification; those methods raise the fuel's carbon footprint despite the fact that it burns cleanly. Chen said oxygen evolution reactions often depend upon an electrocatalyst using a "noble metal" - iridium, platinum or ruthenium. But those are expensive and not readily available. "In this work, we discovered a highly active and stable electrocatalyst based on earth-abundant elements, which even outperforms the noble metal based ones," she said. "Our discovery may lead to a more economic approach for hydrogen production from water electrolysis." Water splitting can be triggered either through electric current or through photocatalysis, using the power of the sun. Direct solar-powered water splitting is too inefficient, as water can absorb just a small portion of the light spectrum. Ideally, Ren said, solar power would be used to generate the electric power used to split water. Explore further: New approach to water splitting could improve hydrogen production More information: Haiqing Zhou el al., "Highly active catalyst derived from a 3D foam of Fe(PO3)2/Ni2P for extremely efficient water oxidation," PNAS (2017). www.pnas.org/cgi/doi/10.1073/pnas.1701562114


News Article | November 14, 2016
Site: www.eurekalert.org

With energy conservation expected to play a growing role in managing global demand, materials and methods that make better use of existing sources of energy have become increasingly important. Researchers reported this week in the Proceedings of the National Academy of Sciences that they have demonstrated a step forward in converting waste heat - from industrial smokestacks, power generating plants or even automobile tailpipes - into electricity. The work, using a thermoelectric compound composed of niobium, titanium, iron and antimony, succeeded in raising the material's power output density dramatically by using a very hot pressing temperature - up to 1373 Kelvin, or about 2,000 degrees Fahrenheit - to create the material. "The majority of industrial energy input is lost as waste heat," the researchers wrote. "Converting some of the waste heat into useful electrical power will lead to the reduction of fossil fuel consumption and CO2 emission." Thermoelectric materials produce electricity by exploiting the flow of heat current from a warmer area to a cooler area, and their efficiency is calculated as the measure of how well the material converts heat - often waste heat generated by power plants or other industrial processes - into power. For example, a material that takes in 100 watts of heat and produces 10 watts of electricity has an efficiency rate of 10 percent. That's the traditional way of considering thermoelectric materials, said Zhifeng Ren, MD Anderson Professor of Physics at the University of Houston and lead author of the paper. But having a relatively high conversion efficiency doesn't guarantee a high power output, which measures the amount of power produced by the material rather than the rate of the conversion. Because waste heat is an abundant - and free - source of fuel, the conversion rate is less important than the total amount of power that can be produced, said Ren, who is also a principal investigator at the Texas Center for Superconductivity at UH. "In the past, that has not been emphasized." In addition to Ren, researchers involved in the project include Ran He, Jun Mao, Qing Jie, Jing Shuai, Hee Seok Kim, Yuan Liu and Paul C.W. Chu, all of UH; Daniel Kraemer, Lingping Zeng and Gang Chen of the Massachusetts Institute of Technology; Yucheng Lan of Morgan State University, and Chunhua Li and David Broido of Boston College. The researchers tweaked a compound made up of niobium, iron and antimony, replacing between 4 and 5 percent of the niobium with titanium. Processing the new compound at a variety of high temperatures suggested that a very high temperature - 1373 Kelvin - resulted in a material with an unusually high power factor. "For most thermoelectric materials, a power factor of 40 is good," Ren said. "Many have a power factor of 20 or 30." The new material has a power factor of 106 at room temperature, and researchers were able to demonstrate an output power density of 22 watts per square centimeter, far higher than the 5 to 6 watts typically produced, he said. "This aspect of thermoelectrics needs to be emphasized," he said. "You can't just look at the efficiency. You have to look also at the power factor and power output."


News Article | November 16, 2016
Site: www.sciencedaily.com

With energy conservation expected to play a growing role in managing global demand, materials and methods that make better use of existing sources of energy have become increasingly important. Researchers reported this week in the Proceedings of the National Academy of Sciences that they have demonstrated a step forward in converting waste heat -- from industrial smokestacks, power generating plants or even automobile tailpipes -- into electricity. The work, using a thermoelectric compound composed of niobium, titanium, iron and antimony, succeeded in raising the material's power output density dramatically by using a very hot pressing temperature -- up to 1373 Kelvin, or about 2,000 degrees Fahrenheit -- to create the material. "The majority of industrial energy input is lost as waste heat," the researchers wrote. "Converting some of the waste heat into useful electrical power will lead to the reduction of fossil fuel consumption and CO2 emission." Thermoelectric materials produce electricity by exploiting the flow of heat current from a warmer area to a cooler area, and their efficiency is calculated as the measure of how well the material converts heat -- often waste heat generated by power plants or other industrial processes -- into power. For example, a material that takes in 100 watts of heat and produces 10 watts of electricity has an efficiency rate of 10 percent. That's the traditional way of considering thermoelectric materials, said Zhifeng Ren, MD Anderson Professor of Physics at the University of Houston and lead author of the paper. But having a relatively high conversion efficiency doesn't guarantee a high power output, which measures the amount of power produced by the material rather than the rate of the conversion. Because waste heat is an abundant -- and free -- source of fuel, the conversion rate is less important than the total amount of power that can be produced, said Ren, who is also a principal investigator at the Texas Center for Superconductivity at UH. "In the past, that has not been emphasized." In addition to Ren, researchers involved in the project include Ran He, Jun Mao, Qing Jie, Jing Shuai, Hee Seok Kim, Yuan Liu and Paul C.W. Chu, all of UH; Daniel Kraemer, Lingping Zeng and Gang Chen of the Massachusetts Institute of Technology; Yucheng Lan of Morgan State University, and Chunhua Li and David Broido of Boston College. The researchers tweaked a compound made up of niobium, iron and antimony, replacing between 4 and 5 percent of the niobium with titanium. Processing the new compound at a variety of high temperatures suggested that a very high temperature -- 1373 Kelvin -- resulted in a material with an unusually high power factor. "For most thermoelectric materials, a power factor of 40 is good," Ren said. "Many have a power factor of 20 or 30." The new material has a power factor of 106 at room temperature, and researchers were able to demonstrate an output power density of 22 watts per square centimeter, far higher than the 5 to 6 watts typically produced, he said. "This aspect of thermoelectrics needs to be emphasized," he said. "You can't just look at the efficiency. You have to look also at the power factor and power output."


News Article | October 3, 2016
Site: www.rdmag.com

Researchers at the University of Houston and Massachusetts Institute of Technology have reported a substantial advance in generating electricity through a combination of concentrating solar power and thermoelectric materials. By combining concentrating solar power – which converts light into heat that is then used to generate electricity – with segmented thermoelectric legs, made up of two different thermoelectric materials, each working at different temperature ranges, researchers said they have demonstrated a promising new alternative solar energy technology. Their findings are published in Nature Energy. Zhifeng Ren, MD Anderson Professor of physics at the University of Houston and an author of the paper, said the work illustrates a new low-cost, nontoxic way to generate power. While it’s not intended to replace large-scale power plants, it could prove especially useful for isolated areas that aren’t on a traditional electric grid, powering small clusters of homes or businesses, for example, he said. In addition to generating electricity, the technology also can produce hot water – valuable for both private and industrial purposes. In addition to Ren, other authors on the paper include Gang Chen, Daniel Kraemer, Kenneth McEnaney, Lee A. Weinstein and James Loomis, all of MIT, and UH researchers Qing Jie, Feng Cao and Weishu Liu. Ren, who also is a principal investigator at the Texas Center for Superconductivity at UH, said the work draws on the researchers’ earlier work, which demonstrated proof of the concept. For this project, supported in part by the Department of Energy, they actually built a device to measure how well optical concentration worked to improve the overall system efficiency. They demonstrated an efficiency of 7.4 percent but reported that based upon their calculations, the device could achieve an efficiency of 9.6 percent. Their previous work resulted in an efficiency of 4.6 percent. “The performance improvement is achieved by the use of segmented thermoelectric legs, a high-temperature spectrally selective solar absorber enabling stable vacuum operation with absorber temperatures up to 600 (degrees) C, and combining optical and thermal concentration,” the researchers wrote. “Our work suggests that concentrating STEGs (solar thermoelectric generators) have the potential to become a promising alternative energy technology.” To gain the higher efficiency, the researchers used a solar absorber, boosted by optical concentrators to increase the heat and improve the energy density. The absorber was placed on legs constructed of thermoelectric materials. While their previous work used only bismuth telluride – a well-known thermoelectric material – this version used skudderudite for the top half of the legs and bismuth telluride for the lower half. Thermoelectric materials produce electricity by exploiting the flow of heat current from a warmer area to a cooler area. By using two materials, the researchers said they were able to take advantage of a broader range of temperatures produced by the solar absorber and boost generating efficiency. Skutterudite, for example, performs best at temperatures above 200 degrees Centigrade, while bismuth telluride works optimally at temperatures below that level. “The record-high efficiencies are achieved by segmenting two thermoelectric materials, skutterudite and bismuth telluride, coupled to a spectrally selective surface operated at close to 600 (degrees) C by combined optical and thermal concentration of the sunlight,” they wrote.


News Article | October 3, 2016
Site: www.cemag.us

Researchers at the University of Houston and Massachusetts Institute of Technology have reported a substantial advance in generating electricity through a combination of concentrating solar power and thermoelectric materials. By combining concentrating solar power — which converts light into heat that is then used to generate electricity — with segmented thermoelectric legs, made up of two different thermoelectric materials, each working at different temperature ranges, researchers said they have demonstrated a promising new alternative solar energy technology. Their findings are published in Nature Energy. Zhifeng Ren, MD Anderson Professor of physics at the University of Houston and an author of the paper, says the work illustrates a new low-cost, nontoxic way to generate power. While it’s not intended to replace large-scale power plants, it could prove especially useful for isolated areas that aren’t on a traditional electric grid, powering small clusters of homes or businesses, for example, he said. In addition to generating electricity, the technology also can produce hot water — valuable for both private and industrial purposes. In addition to Ren, other authors on the paper include Gang Chen, Daniel Kraemer, Kenneth McEnaney, Lee A. Weinstein, and James Loomis, all of MIT, and UH researchers Qing Jie, Feng Cao, and Weishu Liu. Ren, who also is a principal investigator at the Texas Center for Superconductivity at UH, says the work draws on the researchers’ earlier work, which demonstrated proof of the concept. For this project, supported in part by the Department of Energy, they actually built a device to measure how well optical concentration worked to improve the overall system efficiency. They demonstrated an efficiency of 7.4 percent but reported that based upon their calculations, the device could achieve an efficiency of 9.6 percent. Their previous work resulted in an efficiency of 4.6 percent. “The performance improvement is achieved by the use of segmented thermoelectric legs, a high-temperature spectrally selective solar absorber enabling stable vacuum operation with absorber temperatures up to 600 (degrees) C, and combining optical and thermal concentration,” the researchers wrote. “Our work suggests that concentrating STEGs (solar thermoelectric generators) have the potential to become a promising alternative energy technology.” To gain the higher efficiency, the researchers used a solar absorber, boosted by optical concentrators to increase the heat and improve the energy density. The absorber was placed on legs constructed of thermoelectric materials. While their previous work used only bismuth telluride — a well-known thermoelectric material — this version used skudderudite for the top half of the legs and bismuth telluride for the lower half. Thermoelectric materials produce electricity by exploiting the flow of heat current from a warmer area to a cooler area. By using two materials, the researchers said they were able to take advantage of a broader range of temperatures produced by the solar absorber and boost generating efficiency. Skutterudite, for example, performs best at temperatures above 200 degrees Centigrade, while bismuth telluride works optimally at temperatures below that level. “The record-high efficiencies are achieved by segmenting two thermoelectric materials, skutterudite and bismuth telluride, coupled to a spectrally selective surface operated at close to 600 (degrees) C by combined optical and thermal concentration of the sunlight,” they wrote.


News Article | November 1, 2016
Site: www.sciencedaily.com

Researchers at the University of Houston have reported a new method for inducing superconductivity in non-superconducting materials, demonstrating a concept proposed decades ago but never proven. The technique can also be used to boost the efficiency of known superconducting materials, suggesting a new way to advance the commercial viability of superconductors, said Paul C.W. Chu, chief scientist at the Texas Center for Superconductivity at UH (TcSUH) and corresponding author of a paper describing the work, published Oct. 31 in the Proceedings of the National Academy of Sciences. "Superconductivity is used in many things, of which MRI (magnetic resonance imaging) is perhaps the best known," said Chu, the physicist who holds the TLL Temple Chair of Science at UH. But the technology used in health care, utilities and other fields remains expensive, in part because it requires expensive cooling, which has limited widespread adoption, he said. The research, demonstrating a new method to take advantage of assembled interfaces to induce superconductivity in the non-superconducting compound calcium iron arsenide, offers a new approach to finding superconductors that work at higher temperatures. Superconducting materials conduct electric current without resistance, while traditional transmission materials lose as much as 10 percent of energy between the generating source and the end user. That means superconductors could allow utility companies to provide more electricity without increasing the amount of fuel used to generate electricity. "One way that has long been proposed to achieve enhanced T s (critical temperature, or the temperature at which a material becomes superconducting) is to take advantage of artificially or naturally assembled interfaces," the researchers wrote. "The present work clearly demonstrates that high T superconductivity in the well-known non-superconducting compound CaFe As (calcium iron arsenide) can be induced by antiferromagnetic/metallic layer stacking and provides the most direct evidence to date for the interface-enhanced T in this compound." Chu's coauthors on the paper include lead author Kui Zhao, a recent UH graduate now at Advanced MicroFabrication Equipment Inc. in Shanghai; Liangzi Deng, Shu-Yuan Huyan and Yu-Yi Xue, both affiliated with the UH Department of Physics and TcSUH, and Bing Lv, a material physicist who recently moved to the University of Texas-Dallas. The concept that superconductivity could be induced or enhanced at the point where two different materials come together -- the interface -- was first proposed in the 1970s but had never been conclusively demonstrated, Chu said. Some previous experiments showing enhanced superconducting critical temperature could not exclude other effects due to stress or chemical doping, which prevented verification, he said. To validate the concept, researchers working in ambient pressure exposed the undoped calcium iron arsenide compound to heat -- 350 degrees Centigrade, considered relatively low temperature for this procedure -- in a process known as annealing. The compound formed two distinct phases, with one phase increasingly converted to the other the longer the sample was annealed. Chu said neither of the two phases was superconducting, but researchers were able to detect superconductivity at the point when the two phases coexist. Although the superconducting critical temperature of the sample produced through the process was still relatively low, Chu said the method used to prove the concept offers a new direction in the search for more efficient, less expensive superconducting materials.


News Article | November 7, 2016
Site: www.materialstoday.com

Researchers at the University of Houston (UH) have reported a new method for inducing superconductivity in non-superconducting materials, demonstrating a concept proposed decades ago but never proven. This technique could also be used to boost the efficiency of known superconducting materials, suggesting a new way to advance the commercial viability of superconductors, said Paul Chu, chief scientist at the Texas Center for Superconductivity at UH (TcSUH) and corresponding author of a paper on the work in the Proceedings of the National Academy of Sciences. "Superconductivity is used in many things, of which MRI (magnetic resonance imaging) is perhaps the best known," said Chu. But the technology used in health care and other fields remains costly, in part because it requires expensive cooling, which has limited widespread adoption. In this work, Chu and his colleagues demonstrate a new method for taking advantage of assembled interfaces to induce superconductivity in the non-superconducting compound calcium iron arsenide, thereby offering a new approach to finding superconductors that work at higher temperatures. Superconducting materials conduct electric current without resistance, while traditional materials can lose as much as 10% of the energy being transmitted between the generating source and the end user. That means superconductors could allow utility companies to provide more electricity without increasing the amount of fuel used to generate the electricity. "One way that has long been proposed to achieve enhanced Tcs (critical temperature, or the temperature at which a material becomes superconducting) is to take advantage of artificially or naturally assembled interfaces," the researchers write in the paper. "The present work clearly demonstrates that high Tc superconductivity in the well-known non-superconducting compound CaFe As (calcium iron arsenide) can be induced by antiferromagnetic/metallic layer stacking and provides the most direct evidence to date for the interface-enhanced Tc in this compound." The concept that superconductivity could be induced or enhanced at the point where two different materials come together – the interface – was first proposed in the 1970s but had never been conclusively demonstrated, Chu said. Some previous experiments showing enhanced Tcs could not exclude the influence of other effects such as stress or chemical doping, which prevented verification, he said. To validate the concept, researchers working at ambient pressures exposed the undoped calcium iron arsenide compound to a relatively low temperature of 350°C, in a process known as annealing. This caused the compound to form two distinct phases, with one phase increasingly converted to the other the longer the sample was annealed. Although neither of the two phases was superconducting, Chu and his colleagues were able to detect superconductivity at the point when the two phases coexist. Although the Tcs of the sample produced through this process was still relatively low, Chu said the method used to prove the concept offers a new direction in the search for more efficient, less expensive superconducting materials. This story is adapted from material from the University of Houston, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


News Article | October 31, 2016
Site: phys.org

The technique can also be used to boost the efficiency of known superconducting materials, suggesting a new way to advance the commercial viability of superconductors, said Paul C.W. Chu, chief scientist at the Texas Center for Superconductivity at UH (TcSUH) and corresponding author of a paper describing the work, published Oct. 31 in the Proceedings of the National Academy of Sciences. "Superconductivity is used in many things, of which MRI (magnetic resonance imaging) is perhaps the best known," said Chu, the physicist who holds the TLL Temple Chair of Science at UH. But the technology used in health care, utilities and other fields remains expensive, in part because it requires expensive cooling, which has limited widespread adoption, he said. The research, demonstrating a new method to take advantage of assembled interfaces to induce superconductivity in the non-superconducting compound calcium iron arsenide, offers a new approach to finding superconductors that work at higher temperatures. Superconducting materials conduct electric current without resistance, while traditional transmission materials lose as much as 10 percent of energy between the generating source and the end user. That means superconductors could allow utility companies to provide more electricity without increasing the amount of fuel used to generate electricity. "One way that has long been proposed to achieve enhanced Tcs (critical temperature, or the temperature at which a material becomes superconducting) is to take advantage of artificially or naturally assembled interfaces," the researchers wrote. "The present work clearly demonstrates that high Tc superconductivity in the well-known non-superconducting compound CaFe2As2 (calcium iron arsenide) can be induced by antiferromagnetic/metallic layer stacking and provides the most direct evidence to date for the interface-enhanced Tc in this compound." Chu's coauthors on the paper include lead author Kui Zhao, a recent UH graduate now at Advanced MicroFabrication Equipment Inc. in Shanghai; Liangzi Deng, Shu-Yuan Huyan and Yu-Yi Xue, both affiliated with the UH Department of Physics and TcSUH, and Bing Lv, a material physicist who recently moved to the University of Texas-Dallas. The concept that superconductivity could be induced or enhanced at the point where two different materials come together - the interface - was first proposed in the 1970s but had never been conclusively demonstrated, Chu said. Some previous experiments showing enhanced superconducting critical temperature could not exclude other effects due to stress or chemical doping, which prevented verification, he said. To validate the concept, researchers working in ambient pressure exposed the undoped calcium iron arsenide compound to heat - 350 degrees Centigrade, considered relatively low temperature for this procedure - in a process known as annealing. The compound formed two distinct phases, with one phase increasingly converted to the other the longer the sample was annealed. Chu said neither of the two phases was superconducting, but researchers were able to detect superconductivity at the point when the two phases coexist. Although the superconducting critical temperature of the sample produced through the process was still relatively low, Chu said the method used to prove the concept offers a new direction in the search for more efficient, less expensive superconducting materials. Explore further: Finding superconducting needles in the metal haystack More information: Interface-induced superconductivity at ∼25 K at ambient pressure in undoped CaFe2As2 single crystals, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1616264113

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