Elasticity of TiO2 rutile to 1800 K

The ambient pressure elastic properties of single-crystal TiO2 rutile are r eported from room temperature (RT) to 1800 K, extending by more than 1200 d egrees K the maximum temperature for which rutile elasticity data are avail able. The magnitudes of the temperature derivatives decrease with increasin g temperature for five of the six adiabatic elastic moduli (C-ij). At RT, w e find (units, GPa): C-11=268(1); C-33=484(2); C-44=123.8(2); C-66= 190.2(5 ); C-23=147(1); and C-12=175(1). The temperature derivatives (units, GPa K- 1) at RT are: (partial derivative C-11/partial derivative T)(P)= -0.042(5); (partial derivative C-33/partial derivative T)(P)=-0.087(6); (partial deri vative C-44/partial derivative T)(P)= -0.0187(2); (partial derivative C-66/ partial derivative T)(P)=-0.067(2); (partial derivative C-23/partial deriva tive T)(P)=-0.025; and (partial derivative C-12/partial derivative T)(P)-0. 048(5) The values for Ks (adiabatic bulk modulus) and Ct (isotropic shear m odulus) and their temperature derivatives are K-S=212(1) GPa; mu=113(1) GPa ; (partial derivative K-S/partial derivative T)(P)=-0.040(4) GPa K-1; and ( partial derivative mu/partial derivative T)(P)= -0.018(1) GPa K-1. We calcu late several dimensionless parameters over a large temperature range using our new data. The unusually high values for the Anderson-Groneisen paramete rs at room temperature decrease with increasing temperature. At high T,howe ver, these parameters are still well above those for most other oxides. We also find that for TiO2, anharmonicity, as evidenced by a non-zero value of [partial derivative ln (K-T)/partial derivative lnV](T), is insignificant at high T, implying that for the TiO2 analogue of stishovite, thermal press ure is independent of volume (or pressure). Systematic relations indicate t hat partial derivative(2)K(S)/partial derivative T partial derivative P is as high as 7x10(-4) K-1 for rutile, whereas partial derivative(2)mu/partial derivative T partial derivative P is an order of magnitude less.