X-RAY DIFFRACTION STUDY ON THE PHASE TRANSITIONS OF BaTiO₃ SINGLE CRYSTAL

Yukio Yoshimura,^a Naotoshi Tokunaga,^a Hiroshi Iwasaki,^a Akira Kojima,^b Hiroshi Sasou,^b and Ken-ichi Tozaki^c

^aFaculty of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan; ^bDepartment of Materials Science, The University of Shiga Prefecture, Hikone, Shiga 522-8533, Japan; ^cDepartment of Physics, Faculty of Education, Chiba University, Chiba 263-8522, Japan (yukio@se.ritsumei.ac.jp)

It is well known that the BaTiO₃ crystal undergoes three phase transitions at 408 K, 278 K and 183 K. Recently we have made precise measurements of physical properties such as heat flow, dielectric constants and displacement currents at each phase transition on both heating and cooling using the “mK-stabilized cell” having fine temperature stability[1]. Samples used are single crystals from three different sources grown by the top-seeded solution growth method. Measurements of the heat flow and other physical properties have revealed that both the 408 K and 183 K transitions are accompanied by complicated multi-step anomaly, whereas the 278 K transition showed a single step.

In order to get structural information related to the results of the physical properties mentioned above, the phase transitions in BaTiO₃ have been reexamined by X-ray single crystal precession method in the temperature range between 420 K and 90 K. As a temperature is lowered from 420 K, the crystal transforms at 408 K from the perovskite cubic phase into a room temperature phase, where a tetragonal and a monoclinicⅠforms coexist. The crystal further transforms its structure at 278 K and 183 K. At 278 K transition, the monoclinicⅠform, one of the coexistence structure, vanishes and the tetragonal lattice changes into another monoclinicⅡ form with twinned crystal suffering a shear distortion in the low temperature phase. The lowest temperature phase below 183 K is an orthorhombic lattice as a single domain with lattice constants a=0.401 nm, b=0.400 nm, and c=0.402 nm.

Reference

1 Kojima, Y. Kawakatsu, H. Sasou, Y.Yoshimura, N. Tokunaga, H. Iwasaki and K. Tozaki, Ferroelectrics, In press.