Elastic constants of yttrium aluminum garnet have been measured in the temperature range 300–1450 K using a combination of Brillouin scattering and refractive index measurements. Associated quantities such as the bulk modulus, anisotropy ratio, and thermo-optic coefficient have been determined.

Acoustic mode frequency, lattice parameter, and refractive index measurements have been carried out on single crystals of cubic stabilized zirconia, ZrO2(xY2O3), in the temperature range 300 to 1450 K, using Brillouin scattering, x-ray diffraction, and interferometric methods, respectively. Elastic constants Cij and associated quantities such as the bulk modulus B=(C11+2C12)/3, the anisotropy ratio A=2C44/(C11−C12), and the Cauchy relation failure Δ=(C12−C44) have been determined from these measurements. The results show a linear reduction in C11 , C12 , and C44 until a characteristic transition temperature Tc, which depends on the dopant concentration x. The linear decrease is understood in terms of normal thermal expansion. Above Tc (1300 K for x=9.4 mol % and 1050 K for x=24 mol %) there are elastic anomalies; significant reductions in C11, (C11-C12)/2 and C44 occur, with an increase in C12 . These effects are considered to result from thermally generated disorder. Detailed examination of the temperature dependence of the Cij as well as B, A, and Δ show some similarities, but also significant differences in comparison with the anomalous elastic behavior corresponding to the high-temperature superionic state of fluorites. The thermally created defect structures formed at high temperatures in cubic zirconia are thus considered to be different from the anion Frenkel disorder formed in fluorites; this is in accord with recent results from computational simulations and high-temperature neutron scattering.

Cu have been determined from high temperature Brillouin Scattering measurements on the anti-fluorite StNctUred compound Li2S. These decrease linearly from 300 to 8WK, but above 804 Ksubstantial reductions occur in C,, and Clt. The results are interpreted in terms of normal thermal expansion and a diffuse superionic transition involving Frenkel disorder on the lithium sublattice.

No abstract

No abstract