Examples of domain studies of electric field or stress-induced phase transitions in the ferroic crystals of cr3b7013cl, cd2nb207 and pb(mg1/3nb2/3)03

Stress or electric field-induced phase transitions have been studied in single crystals of Cr-Cl boracite, Cd2Nb2O7 and Pb(Mgj/3iNb2/3)°3 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 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, biréfringent on (100)cu^ and (110)cub and optically isotropic on (100)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.