Birefringence of PrAlO3 in the vicinity of 118 K

We have measured the birefringence of PrAlO₃ from 300 to 77 K in several different crystalline orientations. The 205 K first order and 151 K second order structural phase transitions are clearly evident as are the effects of twinning below 151 K which take the form of regular oscillations. Near 118 K we have observed anomalies in the amplitude and frequency of the twinning effect which may relate to the Anderson-Blount phase transition reported by Fleury. Direct evidence of the 118 K transition was also obtained when birefringence measurements were taken in a geometry chosen to suppress the twinning effect.