Resonant ultrasound studies of the layered perovskite system Ca2-xSrxRuO4

The elastic response of the layered perovskite system Ca(2-x)Sr(x)RuO(4) (0.2< or =x< or =2) has been studied as a function of temperature and doping concentration x using resonant ultrasound spectroscopy. The elastic constants c(11) and c(44) have been obtained for three polycrystalline samples (x=1.0, 0.5, and 0.3) and show a softening trend with increasing Ca-content. In addition, the temperature-dependence of the elastic response of five single-crystals (x=2.0, 1.9, 0.5, 0.3, and 0.2) has been measured. For 2.0> or =x> or =0.5, a dramatic softening over a wide temperature range is observed upon cooling, which is attributed to the rotational instability of RuO(6) octahedra (for x=2.0 and 1.9) and the static rotation of the octahedra (for x=0.5). For the Ca-rich samples (x=0.3 and 0.2), the softening occurs in a very narrow temperature range, corresponding to the structural phase transition from high-temperature tetragonal to low-temperature orthorhombic symmetry.