Temperature Dependence of the Order Parameter in Ferroelectric LiTaO3

Accurate measurements of birefringence in LiTaO3:Cr+ single crystals in the interval 100 K ≤ T ≤ 1000 K have been performed. The temperature dependence of the order parameter, the square root of the birefringence change, has been shown to produce a clear second order ferroelectric phase transition in this distorted perovskite. The results are compared with those obtained for spontaneous polarization from pyroelectric current measurements.