TEMPERATURE-DEPENDENT RAMAN-SCATTERING IN KTIOPO4 AND KTIOASO4 SINGLE-CRYSTALS

The longitudinal (LO) and transverse (TO) A(1) vibrational modes have been measured between 30 and 1200 cm(-1) as a function of temperature (30-1240 K) for both KTiOPO4 (KTP) and KTiOAsO4 (KTA). KTP and KTA exh ibit an obviously different Raman spectra in the frequency region 400- 650 cm(-1) (with respect to KTA). This middle-frequency difference is attributed to the substitution ions in XO(4) group (X=P or As) modifin g the force constant of crystal. The relative intensities of the low-f requency bands increase dramatically with increasing temperature due t o high mobility of K+ ion. There is no typical soft-mode like behavior in the measured frequency range. A higher symmetric structure taking place above T-c has been confirmed by the disappearance of the A(1g)(L O) stretching modes of TiO6 group. Comparison of each frequency belong ing to the symmetry A(1), A(2), B-1, and B-2 measured along the [110] phonon direction shows complex difference. The vibrational frequencies of various symmetries were also obtained. (C) 1996 American Institute of Physics.