Ferroelectric phase transitions and properties of nonlinear optical crystals of KTiOPO4 and its analogs

Single crystals of new efficient nonlinear optical compounds KTiOPO₄ (KTP), RbTiOPO₄ (RTP), and TlTiOPO₄ (TTP) were grown from molten solutions and some characteristics of their physical properties were investigated. The temperature dependences of the intensity of the second harmonic of laser radiation generated in these crystals and of their permittivities revealed a second-order ferroelectric phase transition at temperatures 934 °C (KTP), 789 °C (RTP), and 581 °C (TTP). Moreover, these crystals exhibited an anomalously high ionic electrical conductivity. The ferroelectricity and the conductivity could affect significantly nonlinear optical characteristics of these crystals.