Correlation of crystalline and magnetic structures of barium ferrites with dual ferroic properties

The spontaneous polarization has been found out in solid solutions of barium ferrites partially substituted with In, Al, Ga and Sc ions that is an evidence of their ferroelectric properties. For explanation reasons of appearance ferroelectric properties in these materials have been investigated features of crystal and magnetic structures with using X-ray and neutron time-of-flight diffraction methods in a wide temperature range. The crystal structure of barium ferrites has been refined in the frameworks of centrosymmetric P6(3)/mmc (No. 194) and non-centrosymmetric P6(3)mc (No. 186) space groups. According to analysis of neutron patterns, the distortion of oxygen octahedrons (tetrahedrons and trigonal-bipyramids) has been observed in unit cells both space groups. It was shown that a key role in appearance of spontaneous polarization can be associated with the absence of inversion center in unit cell.