Examples of domain studies of electric field or stress-induced phase transitions in the ferroic crystals of Cr₃B₇O₁₃Cl, Cd₂Nb₂O₇ and Pb(Mg₁/₃Nb₂/₃)O₃

Stress or electric field-induced phase transitions have been studied in single crystals of Cr-Cl boracite, Cd2Nb2O7 and Pb(Mg1/3Nb2/3O3 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 43m/42m interface at 264 K. Application of an electric field to the 42m phase can induce a mm2 phase, as wa characterized by an antiferroelectric behaviour. In the Cd2Nb2O7 crystals a field-induced phase ttransition 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//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