Synthesis of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>Mg</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:msub> <mml:mi>IrH</mml:mi> <mml:mn>5</mml:mn> </mml:msub> </mml:mrow> </mml:math> : A potential pathway to high- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>c</mml:mi> </mml:msub> </mml:math> hydride superconductivity at ambient pressure
Mads F. Hansen, Lewis J. Conway, Kapildeb Dolui, Christoph Heil, Chris J. Pickard, Anna Pakhomova, Mohamed Mézouar, Martin Kunz, Rohit P. Prasankumar, Timothy A. Strobel
Abstract
Following long-standing predictions associated with hydrogen, high-temperature superconductivity has recently been observed in several hydride-based materials. Nevertheless, these high-${T}_{c}$ phases only exist at extremely high pressures, and achieving high transition temperatures at ambient pressure remains a major challenge. Recent predictions of the complex hydride ${\mathrm{Mg}}_{2}{\mathrm{IrH}}_{6}$ may help overcome this challenge with calculations of high-${T}_{c}$ superconductivity ($65\phantom{\rule{0.28em}{0ex}}\mathrm{K}<{T}_{c}<170\phantom{\rule{4.pt}{0ex}}\text{K}$) in a material that is stable at atmospheric pressure. In this paper, the synthesis of ${\mathrm{Mg}}_{2}{\mathrm{IrH}}_{6}$ was targeted over a broad range of $P\text{\ensuremath{-}}T$ conditions, and the resulting products were characterized using x-ray diffraction (XRD) and vibrational spectroscopy, in concert with first-principles calculations. The results indicate that the charge-balanced complex hydride ${\mathrm{Mg}}_{2}{\mathrm{IrH}}_{5}$ is more stable over all conditions tested up to approximately 28 GPa. The resulting hydride is isostructural with the predicted superconducting ${\mathrm{Mg}}_{2}{\mathrm{IrH}}_{6}$ phase except for a single hydrogen vacancy, which shows a favorable replacement barrier upon insertion of hydrogen into the lattice. Bulk ${\mathrm{Mg}}_{2}{\mathrm{IrH}}_{5}$ is readily accessible at mild $P\text{\ensuremath{-}}T$ conditions and may thus represent a convenient platform to access superconducting ${\mathrm{Mg}}_{2}{\mathrm{IrH}}_{6}$ via nonequilibrium processing methods. Finally, the critical factors influencing the calculated range of superconducting transition temperatures for this material are discussed.