BEHAVIOR OF ELASTIC-CONSTANTS, REFRACTIVE-INDEX, AND LATTICE-PARAMETER OF CUBIC ZIRCONIA AT HIGH-TEMPERATURES

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 C(ij) and associated quantities such as the bulk modulus B=(C-11+2C-12)/3, the anisotropy ratio A=2C44/(C-11-C-12), and the Cauchy relation failure DELTA=(C-12-C44) have been determined from these measurements. The results show a linear reduction in C-11, C-12, and C44 until a characteristic transition temperature T(c), which depends on the dopant concentration x. The linear decrease is understood in terms of normal thermal expansion. Above T(c) (1300 K for x=9.4 mol % and 1050 K for x=24 mol %) there are elastic anomalies; significant reductions in C-11, (C-11-C-12)/2 and C44 occur, with an increase in C-12. These effects are considered to result from thermally generated disorder. Detailed examination of the temperature dependence of the C(ij) as well as B, A, and DELTA 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.