Investigation of the structure, physical properties, and phase transition in SrAlF5

Crystals of SrAlF5 have been grown by the Bridgman method from the melt and by sintering of the components. Optical polarization studies and measurements of the thermal expansion and birefringence coefficients have been carried out over a wide temperature range. The electromechanical coefficient d (33) has been measured, and the optical second harmonic, dielectric hysteresis loop, and optical quality of the crystal have been assessed. X-ray diffraction investigations have been performed to identify the revealed compounds. It has been demonstrated that the SrAlF5 crystals obtained under the growth conditions chosen have I4(1)/a symmetry and do not undergo structural phase transitions in the temperature range 100-800 K. Crystalline inclusions of the AlOF oxyfluoride have been revealed in crystals grown with an AlF3 excess. The birefringence of the AlOF crystal is an order of magnitude higher than that of SrAlF5, does not depend on temperature, and has no anomalies up to 800 K.