Superconducting Zirconium Polyhydrides at Moderate Pressures

Abstract

Highly compressed hydrides have been at the forefront of the search for high-<i>T</i>_c superconductivity. The recent discovery of record-high <i>T</i>_c's in H₃S and LaH_10±<i>x</i> under high pressure fuels the enthusiasm for finding good superconductors in similar hydride groups. Guided by first-principles structure prediction, we successfully synthesized ZrH₃ and Zr₄H₁₅ at modest pressures (30-50 GPa) in diamond anvil cells by two different reaction routes: ZrH₂ + H₂ at room temperature and Zr + H₂ at ∼1500 K by laser heating. From the synchrotron X-ray diffraction patterns, ZrH₃ is found to have a <i>Pm</i>3̅<i>n</i> structure corresponding to the familiar A15 structure, and Zr₄H₁₅ has an <i>I</i>4̅3<i>d</i> structure isostructural to Th₄H₁₅. Electrical resistance measurement and the dependence of <i>T</i>_c on the applied magnetic field of the sample showed the emergence of two superconducting transitions at 6.4 and 4.0 K at 40 GPa, which correspond to the two <i>T</i>_c's for ZrH₃ and Zr₄H₁₅.