Synthesis of superconducting hcp- ZrH3 under high hydrogen pressure

Abstract

Zirconium trihydride and, for comparison, trideuteride with hexagonal close-packed (hcp) metal lattices were synthesized at a hydrogen/deuterium pressure of 9 GPa and a temperature of 873 K using toroid-type high-pressure chambers. After a rapid cooling (quenching) to 100 K and lowering the pressure to atmospheric, the quenched sample was removed from the chamber and studied by hot extraction analysis, powder x-ray diffraction, and ac magnetic susceptometry. The hot extraction showed that thermal decomposition of both hcp-${\mathrm{ZrH}}_{3}$ and hcp-${\mathrm{ZrD}}_{3}$ in vacuum begins after heating at a rate of 10 K/min to \ensuremath{\sim}200 K and almost ceases at 270 K, leaving tetragonal $\ensuremath{\varepsilon}\text{\ensuremath{-}}{\mathrm{ZrH}}_{2}/\ensuremath{\varepsilon}\text{\ensuremath{-}}{\mathrm{ZrD}}_{2}$ as a result. The x-ray diffraction study at 85 K gave lattice parameters $a=3.443(2)\phantom{\rule{0.16em}{0ex}}\AA{}$ and $c=5.964(4)\phantom{\rule{0.16em}{0ex}}\AA{}$ for hcp-${\mathrm{ZrH}}_{3}$ and somewhat smaller values of $a=3.430(5)\phantom{\rule{0.16em}{0ex}}\AA{}$ and $c=5.947(5)\phantom{\rule{0.16em}{0ex}}\AA{}$ for hcp-${\mathrm{ZrD}}_{3}$. The measurements of magnetic susceptibility revealed superconductivity with an onset at 11.6(1) K for hcp-${\mathrm{ZrH}}_{3}$ and 9.5(2) K for hcp-${\mathrm{ZrD}}_{3}$.