Structures and Transport Properties of Hydrogenated TiZr Alloys under High Pressure

Effects of pressure on the structure, electronic resistance, and the critical magnetic field for hydrogenated TiZr alloys were investigated to study the transport properties of hydrogen-absorbing materials under compression. With increasing pressure from ambient to 50 GPa, results of synchrotron-based X-ray diffraction measurement revealed that the structure of the pure TiZr alloys prepared at equiatomic composition changed from an hcp to a bcc phase through an hcp-omega phase, while hydrogenated ones exhibit various intermediate phases including orthorhombic-gamma and tetragonal phases. Superconducting transition temperature, Tc, of pure TiZr alloys, increased from 2.7 K to 11.7 K with increasing pressure from 5.4 GPa, and 50 GPa, respectively. Interestingly, the Tc values for hydrogenated samples increased from 3.4 K to 9.4 K at 6 GPa and 32 GPa, respectively, but decreased to 8 K with increasing pressure further to 55 GPa. The Tc values were suppressed under the magnetic field and the critical field for the hydrogenated one is less than the one of pure state at 50 GPa. Our combined results of structure and transport measurements suggest that applying pressure increases the Tc while hydrogen atoms form an irreversible hydride phase and decrease the Tc. The contribution of hydrogen for increasing Tc in transition metals is different from the ones observed in polyhydrides exhibiting near room temperature of Tc under high pressure.