Far-infrared soft-mode behavior in PbSc1∕2Ta1∕2O3 thin films

摘要: Temperature dependences of the optic phonons in $\rm PbSc_{1/2}Ta_{1/2}O_3$ sol-gel films deposited on sapphire substrates were studied by means Fourier transform far-infrared transmission spectroscopy temperature range 20-900\K. Four displaying different B-site order with both ferroelectric and relaxor behavior studied. In all cases TO mode near 80\icm{} at 10\K{} softens heating to $\approx$45\icm{} following Cochran law extrapolated critical 700\K{} (400\K{} above dielectric maximum, $T_{\rm m}$), but 600\K{} its frequency remains stabilized. It can be assigned A$_{1}$ component soft inside polar clusters which form below Burns 700\K. ordered PST film another activates T$_{m}$ infrared spectra 60\icm exhibiting also anomalous dependence due coupling former mode. is F$_{2g}$ Raman active Central mode, appears THz range, dynamics clusters. slows down cooling vanishes from our spectral m}$. Another overdamped excitation E 30\icm{} low temperatures.