Far-infrared and THz spectroscopy of 0.4PMN–0.3PSN–0.3PZN relaxor ferroelectric ceramics

Temperature dependence of the optic phonons in 0.4PbMg1/3Nb2/3O3–0.3PbSc1/2Nb1/2O3–0.3PbZn1/3Nb2/3O3 (0.4PMN–0.3PSN–0.3PZN) ceramics were studied by means of FTIR reflection and THz transmission spectroscopy in the temperature range of −253.15 to 226.85 °C. On heating from low temperatures, the A1 component of the strongly split TO1 mode softens towards the Burns temperature, but the softening ceases near 126.85 °C which could be a signature of polar cluster percolation temperature. Surprisingly, the TO2 mode also softens on heating and follows the Cochran law with extrapolated critical temperature close to the melting point.