Theoretical Study of the Ferroelastic Domain Structure in $La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{3-x}$

Theoretical analysis of the ferro-elastic domain structure of a $La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{2.925}$ crystal in three different crystallographic phases is presented. Parameters of these configurations are obtained using group theoretical approach, the method of spontaneous deformation as well as theoretical interpretation of twinning resulting from mechanical deformation (mechanical twinning theory). In the three phases of $La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{2.95}$ - trigonal, orthorhombic and monoclinic - the parameters of ferro-elastic domain structures are determined; namely the quantity of orientation states, symmetry elements of connection between states, orientations and types of domain walls, tensors of spontaneous deformations of the perovskite-type cells for every orientation state, elements of twin shifts, which are needed for the reorientation of some orientation states to others. By using the found parameters of bidomain configurations a mechanism is proposed, which causes chevron-like domain configurations in compounds with martensitic phase transitions.