Interplay between structural instability and lattice dynamics inEuRh2(PxAs1−x)2

Abstract

The interplay between the crystallographic structure, valence state, and lattice dynamics of the series ${\mathrm{EuRh}}_{2}({\mathrm{P}}_{x}{\mathrm{As}}_{1\ensuremath{-}x}{)}_{2}$ $(x=0,$ 0.5, and 1) has been investigated using x-ray diffraction, the ${}^{151}\mathrm{Eu}$ M\"ossbauer effect, and the ${}^{151}\mathrm{Eu}$ nuclear inelastic scattering of synchrotron radiation, respectively. We show that the first-order, isostructural phase transition $(\ensuremath{\alpha}\mathrm{phase}\ensuremath{\rightarrow}\ensuremath{\beta}\mathrm{phase}),$ which occurs at ${x}_{\mathrm{c}}\ensuremath{\approx}0.85,$ is not connected with a change of the ${\mathrm{Eu}}^{2+}$ valence state but is associated with a significant modification of the Eu partial phonon density of states (PDOS). Lattice dynamical calculations on ${\mathrm{EuRh}}_{2}({\mathrm{P}}_{x}{\mathrm{As}}_{1\ensuremath{-}x}{)}_{2}$ show that the observed change in the PDOS can be attributed to the structural change at the phase transition.