Thermal expansion and lattice anharmonicity of Pd-H and Pd-D alloys

The authors have made thermal expansion measurements on Pd-H and Pd-D alloys. The measurements were performed between 9 and 270K, and with H(D) concentrations ranging from 0.69 to 0.82 H(D)/Pd atom ratios. Above 80K (in pure beta phase), the thermal expansion of Pd-H and Pd-D is increased compared with that of pure Pd, for comparable concentrations, D-doped samples have a larger expansion than those doped with H. For PdH 0.7 (PdD 0.7 ), the authors find an essentially isotope-independent Gruneisen constant gamma H =3.0+or-0.7 for the optical phonons and a Gruneisen constant gamma ac =3.0+or-0.5 for the acoustic phonons.