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Synthesis of superconducting hcp-ZrH3 under high hydrogen pressure
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-ZrH3 and hcp-ZrD3 in vacuum begins after heating at a rate of 10 K/min to ∼200 K and almost ceases
at 270 K, leaving tetragonal ε-ZrH2/ε-ZrD2 as a result. The x-ray diffraction study at 85 K gave lattice
parameters a = 3.443(2)Å and c = 5.964(4)Å for hcp-ZrH3 and somewhat smaller values of a = 3.430(5)Å
and c = 5.947(5)Å for hcp-ZrD3. The measurements of magnetic susceptibility revealed superconductivity with
an onset at 11.6(1) K for hcp-ZrH3 and 9.5(2) K for hcp-ZrD3.