Examples of domain studies of electric field or stress-induced phase transitions in the ferroic crystals of Cr₃B₇O₁₃Cl, Cd₂Nb₂O₇ and Pb(Mg_1/3Nb_2/3)O₃

Abstract

Stress or electric field-induced phase transitions have been studied in single crystals of Cr-Cl boracite, Cd₂Nb₂O₇ and Pb(Mg_1/3Nb_2/3)O₃ by means of polarized light microscopy associated with electric characterizations. A mm2 phase was found to be induced in Cr-Cl by spontaneous stress at the mechanically non-matching 3m/2m interface at 264 K. Application of an electric field to the 2m phase can induce a mm2 phase, as was characterized by an antiferroelectric behaviour. In the Cd₂Nb₂O₇ crystals a field-induced phase transition mm2(pp) → mm2(ss) was observed. A macroscopically polar phase can be induced in PMN by E, with appearance of macrodomains, birefringent on (100)_cub and (110)_cub and optically isotropic on (111)_cub (O.A. & // < 111> _cub). The symmetry of the induced phase was deduced to be trigonal 3m. The polarized light microscopy was shown to be a powerful tool for studying the induced phase transitions in ferroic materials.

Key Words:

• induced phase transition
• domains
• Cr₃B₇O₁₃Cl
• Cd₂Nb₂O₇
• Pb(Mg_1/3Nb_2/3)O₃