Crystallo‐optical properties of the Sm x Tb 1− x FeO 3 orthoferrites

The paper reports the results of X‐ray diffraction studies as well as the angular dependences of rotation of the plane of polarization and birefringes of the Sm x Tb 1− x FeO 3 crystals ( x = 0; 0.2; 0.4; 0.55; 0.8; 1). The polar diagrams presented for the plane (001) have the symmetry mm2, while for (110), the symmetry lowers up to the axis of a second order. The gyrotropic measurements made have allowed us to refer the Sm x Tb 1− x FeO 3 to a planar class of an orthorhombic crystal system with the space group C 2v 9 –Pn2a, class mm2. – The magnitude of birefringence for the Sm x Tb 1− x FeO 3 is found to be sensitive both to a crystallographic direction and a composition, the greatest values stand for (110). For (001), a non‐monotonous birefringence variation with the composition is observed. The angles between optic axes, calculated by the birefringence magnitudes, are in fair agreement with gyrotropic data for the compositions x = 0.55 – 1.