High temperature elastic constants of rare-earth doped Sr_0.9X_0.1TiO_3-δ (X = Pr, Y)

Temperature dependence of the elastic constants of polycrystalline rare-earth doped strontium titanate (STO) [ Sr_0.9X_0.1TiO_3-δ (X = Pr, Y)] was investigated in the temperature range of 300 K—750 K using resonant ultrasound spectroscopy. Elastic constants of undoped STO decrease linearly indicating typical softening with increased temperature. Yttrium (Y) doped STO also exhibits a monotonic softening, however, with a pronounced curvature in this high temperature regime. Trends of elastic constants of the praseodymium (Pr) doped STO show a non-monotonic stiffing from room temperature to 475 K, followed by a gradual softening. Changes in attenuation were quantified by the inverse quality factor (1/Q) averaged over measured resonances. Undoped STO showed a monotonic gradual increase of attenuation with increasing temperature while yttrium doped STO showed little variation. In contrast, attenuation of Pr doped STO exhibited a peak around 425 K. These results will be compared to thermal conductivity measurements in the same temperature range and phonon scattering mechanisms will be discussed.