Optical nonlinear properties and structural phase transitions in new promising ferroelectric family LnBXO(5) (Ln-La, Pr; X-Ge, Si)

The new family of ferroelectric oxides presented and some its properties including nonlinear optical properties of LaBGeO5 (LBGO) are considered. It is shown that these oxides have high Curie temperatures, symmetry change P3(1)21 --> P3(1) and the mixed displacive and order disorder type of the phase transitions. All second harmonic generation (SHG), tensor components are determined for LBGO crystals and the magnitude of the spontaneous polarization is evaluated from the vector part of SHG tensor as 2,4 +/- 0,8 mu C/cm(2). The phase transitions in PrBGeO5 and LaBSiO5 crystals are considered taking into account SHG data for powder samples.