High-temperature vibrational spectra, relaxation and ionic conductivity effects in KTiOPO4

High-temperature Raman and infrared spectra measurements have been performed on KTiOPO4 single crystals in a temperature range from room temperature to 1000 K. Special attention is paid to the low-frequency Raman spectra which exhibit an anomalously large quasi-elastic scattering: this appears with an increase in temperature. The Raman spectra were fitted using a response function involving one oscillator and two Debye relaxations. The resulting parameters are analysed and discussed in order to clarify the phase transition mechanism and, more specifically, the influence of the potassium (K) ion on this transition and on the ionic conductivity. The high-temperature infrared reflectivity spectra were fitted for the two polar mode configurations A1 and B2 and have been analysed critically within the previously-mentioned framework.