The Pressure Effect On Crystal Structure Of Complex Ferroelectrics Ba4sm2fe2nb8o (30) And Ba4gd2fe2nb8o30

The crystal structure of complex oxide ferroelectrics Ba4Sm2Fe2Nb8O30 and Ba4Gd2Fe2Nb8O30 have been studied by means of energy-dispersive X-ray diffraction method at high pressure up to 4 GPa at room temperature. At ambient pressure, the crystal structure of both compounds is described by the tetragonal symmetry with space group P4/mbm. At pressure P similar to 1.8 GPa in Ba4Sm2Fe2Nb8O30 and at P similar to 2.2 GPa in Ba4Gd2Fe2Nb8O30 the structure phase transition have been observed. The orthorhombic structure model with Pba2 space group for high-pressure phase of those compounds have been proposed. The baric dependences of lattice parameters and unit cell volumes of Ba4Sm2Fe2Nb8O30 and Ba4Gd2Fe2Nb8O30 compounds have been obtained.