Optical properties of TlInS2 layered crystal under pressure

Studies of the optical properties of TlInS₂ layered ferroelectric with an incommensurate phase were performed. In the temperature range 190-220 K at atmospheric pressure, we observed rotation of the plane of the optical axes and a change of the angle between the optical axes of the crystal. The temperature dependences of birefringence and its anomalous part were investigated, the anomalies at T _c =192 K and T _i =214 K, corresponding to structural phase transitions, were revealed. Pressure increase in the range p _atm≤p<470 MPa is shown to result in a shift of the birefringence anomalies towards higher temperatures.