High temperature Raman spectra was recorded in this paper.The phase transition of β BaB 2O 4(BBO),a widely used crystal and potassium lithium niobate (KLN)crystal,a newly crystal was studied by the Raman spectra.The phase transition temperature of BBO from β BaB 2O 4 to α BaB 2O 4 was confirmed to be about 927℃ and 500℃ of KLN from ferro electric phase to para electric phase.It was observed that the change of the distribution of Ba 2+ and the change of the structure of [B 3O 6] 3- rings were important symbols of the phase transition of BBO.The finger peak (629cm -1 )belonged to [B 3O 6] 3- rings still existed when the temperature was up to 1400K.This indicated that the basic growing unit of BBO was[B 3O 6] 3- rings not atoms.The phase transition of KLN was mainly due to the position shifting of all the particles at the transition point.The movement of Li + ions had great influence on the vibration modes in the crystal. The relation between the phase transition and the efficiency of frequency doubling was also studied.It was often observed that when the power of the incident light was increased to a certain degree,the conversion efficiency was no longer increased.This mainly because the phase transition temperature of the crystal was lower and phase transition occurred in the crystal.
