Composition dependence of the elastic constants of $\beta $ and ($\alpha $~+~$\beta {\rm p}$-phase PdH$_{x}$

Previously [1], we measured the room-temperature elastic constants of PdH$_{x}$ for 0~$<$~$x$~$<$~0.75. These measurements were done on single crystals of $\alpha $-phase Pd(H) solid solution ($x$~$<$~0.01), of $\beta $-phase Pd-H hydride ($x$~$>$~0.62), and of coherent two-phase mixtures of $\alpha +\beta $ phases (0.01$