Pressure dependence of the transitions to the incommensurate phase of barium sodium niobate

The application of hydrostatic pressure (up to 1.2 kbar) smoothly modifies the characteristics of the incommensurate phase of barium sodium niobate, as described by optical birefringence measurements. The lower limit $T_L$ of the phase increases with pressure (+14.2±0.8 °C/kbar). The upper limit $T_I$ appears less affected. In addition to a narrowing of the incommensurate phase, one infers that, on increasing the pressure, the discontinuous character of the transition at $T_L$ becomes less pronounced.