Microscopic Observation of Ferroelectric and Structural Phase Transitions in SrTiO3 under Uniaxial Stress Using Birefringence Imaging Techniques

Stress-induced ferroelectric phase transition of SrTiO3 was microscopically observed using birefringence imaging techniques. Although there are many studies on ferroelectric state, the experiments under external force (abbreviated as sigma converted to pressure) have been scarcely developed. This is because the dielectric and structural properties are locally disturbed by the nonuniform lattice distortion when sigma is applied; however, it was not easy to quantitatively evaluate them. In this study, the spatial distribution of the dielectric and structural properties under sigma was clarified by retardance and fast-axis direction images. When sigma vertical bar vertical bar [001], the ferroelectric state induced by normal stress appears almost uniformly below similar to 20 K contrary to the coexistence of the ferroelectric and quantum paraelectric states under a high electric field. However, when sigma vertical bar vertical bar [1 (1) over bar0], both normal and shear stresses are simultaneously generated, resulting in the appearance of domains with complex shapes around dislocations in the tetragonal phase. Distributions of the retardance and the fast-axis direction exhibit concentration of the lattice distortion, and the structural phase transition temperatures are nonuniformly spread. From the temperature dependence of the retardance in each domain, there is no indication of the ferroelectric phase transition, probably because the lattice distortion never reaches the critical value.