Thermal expansion coefficients of strontium - barium niobate single crystals in the vicinity of the phase transition point

High quality of solid solution single crystals SrxBa1-xNb2O6 (0.35 < x < 0.72) obtained by the Czochralski method were investigated. The lattice parameters of these single crystals were determined, using X-ray measurements, with an uncertainty as low as of the order of Delta d/d = 10(-5). Registered temperature changes of lattice parameters have permitted to calculate thermal expansion coefficients with low relative uncertainties, which were determined in the temperature range from 293 to 323 K along [100] and [001] directions. Based on the thermal expansion coefficients it was possible to assign the phase transition temperature - T-C for all studied compositions. Additionally, the observed character of changes of the linear thermal expansion coefficients clearly indicates a possible first-order character of the investigated structural phase transition.