Abstract
Inelastic neutron scattering studies of Zr0.85Ca0.15O1.85 at 300, 1200 and 1500 K show LA and TA phonons rapidly broadening with phonon wavevector q in all observed directions ((00 xi ),( xi xi 0),( xi xi xi ), (- xi /2, - xi /2, xi )). Optical phonon branches could not be observed. Both results can be related to the underlying static disorder. Comparative studies of well ordered CeO2 show that the influence of anharmonicities is negligible in both these oxides up to temperatures of 1500 K. The phonon linewidths of Zr0.85Ca0.15O1.85 are exceptionally large at 1200 K. This can be related to phase diagram boundaries occurring in this temperature regime. The temperature dependence of the linewidths is associated with the hindered cubic:tetragonal phase transition. The line broadening is markedly anisotropic. Elastic constants c11, c12 and c44 were derived from the data at 1200 K.
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