Raman scattering and x-ray diffraction studies of polycrystalline $\mathrm{Ca}{\mathrm{Cu}}_3{\mathrm{Ti}}_4{\mathrm{O}}_{12}$ under high-pressure

We report Raman scattering and x-ray diffraction studies of polycrystalline $\mathrm{Ca}{\mathrm{Cu}}_3{\mathrm{Ti}}_4{\mathrm{O}}_{12}$ (CCTO) under high pressures. The pressure dependence of several Raman modes was investigated. No anomalies have been observed on the phonon spectra thereby indicating that the $T_h$ $\left(\mathit{Im}\overline{3}\right)$ structure remains stable up to the maximum pressure $\left(5.3\mathrm{GPa}\right)$ we reached in this experiment. The pressure coefficients for the observed Raman modes were determined. This set of parameters was used for evaluating the stress developed in CCTO thin films. The high-pressure x-ray studies were extended up to $46\mathrm{GPa}$ and the data confirmed that the $T_h$ structure remains stable up to this pressure. The pressure-volume data are well described by the Birch’s equation of state. The experimental value of the zero pressure bulk modulus is $B_0=212\pm 2\mathrm{GPa}$. Grüneisen parameters of CCTO were also determined.

Figure 1

Pressure dependent Raman spectra of CCTO obtained during (a) compression and (b) decompression runs.

Figure 2

Frequency vs pressure plots for CCTO Raman modes. The solid and open circles stand for compression and decompression runs, respectively. The error bar for both frequency $(\pm 1.5{\mathrm{cm}}^{-1})$ and pressure $(\pm 0.1\mathrm{GPa})$ are smaller than the symbols. The solid lines are fit to the experimental data using $\omega \left(P\right)={\omega }_0+\alpha P$.

Figure 3

Energy-dispersive diffraction patterns of $\mathrm{Ca}{\mathrm{Cu}}_3{\mathrm{Ti}}_4{\mathrm{O}}_{12}$ recorded at (a) $4.0\mathrm{GPa}$ and (b) $24.0\mathrm{GPa}$ The inset to panel (b) stands for the pressure-volume compression data of $\mathrm{Ca}{\mathrm{Cu}}_3{\mathrm{Ti}}_4{\mathrm{O}}_{12}$. The curve through the experimental points has been calculated from the Birch’s equation [see Eq. (1)].