Materials scientists at Argonne National Laboratory synthesized single crystals of a metallic trilayer nickelate compound, which shows similarities to a technologically valuable class of materials called high-temperature superconductors — and with the right ingredients, could potentially become one. Above: The crystal structure of such a compound. Credit: Zhang et. al
A team at DOE Argonne National Laboratory has identified a nickel oxide compound as an unconventional but promising candidate material for high-temperature superconductivity. The team successfully synthesized single crystals of a metallic trilayer nickelate compound, a feat the researchers believe to be a first. “It’s poised for superconductivity in a way not found in other nickel oxides. We’re very hopeful that all we have to do now is find the right electron concentration.”
High-temperature superconductors could lead to faster, more efficient electronic devices, grids that can transmit power without energy loss and ultra-fast levitating trains that ride frictionless magnets instead of rails. After 3 decades of research, exactly how cuprate superconductivity works remains a defining problem. One approach to solving this problem has been to study compounds that have similar crystal, magnetic and electronic structures to the cuprates.
Materials scientists at Argonne National Laboratory synthesized these single crystals of a metallic trilayer nickelate compound via a high-pressure crystal growth process. A team led by John Mitchell, an Argonne Distinguished Fellow and …more
Nickel-based oxides – nickelates – have long been considered as potential cuprate analogs because the element sits immediately adjacent to copper in the periodic table. Thus far, Mitchell noted, “That’s been an unsuccessful quest…None of these analogs have been superconducting, and few are even metallic.”
The nickelate that the Argonne team has created is a quasi-2D trilayer compound, ie it consists of 3 layers of nickel oxide that are separated by spacer layers of praseodymium oxide. “Thus it looks more two-dimensional than three-dimensional, structurally and electronically,” Mitchell said. This nickelate and a compound containing lanthanum rather than praseodymium both share the quasi-two-dimensional trilayer structure. But the lanthanum analog is non-metallic and adopts a so-called “charge-stripe” phase, an electronic property that makes the material an insulator, the opposite of a superconductor. “For some yet-unknown reason, the praseodymium system does not form these stripes,” Mitchell said. “It remains metallic and so is certainly the more likely candidate for superconductivity.”
Argonne is one of a few laboratories in the world where the compound could be created. The Materials Science Division’s high-pressure optical-image floating zone furnace has special capabilities. It can attain pressures of 150 atmospheres and temperatures of approximately 2,000 degrees Celsius, conditions needed to grow the crystals.
The research team verified that the electronic structure of the nickelate resembles that of cuprate materials by taking X-ray absorption spectroscopy measurements at the Advanced Photon Source, a DOE Office of Science User Facility, and by performing density functional theory calculations. Materials scientists use density functional theory to investigate the electronic properties of condensed matter systems.
“I’ve spent my entire career not making high-temperature superconductors,” Mitchell joked. But that could change in the next phase of his team’s research: attempting to induce superconductivity in their nickelate material using a chemical process called electron doping, in which impurities are deliberately added to a material to influence its properties.
http://www.anl.gov/articles/nickel-thought-compound-shows-potential-high-temperature-superconductivity
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