CUBIC-TETRAGONAL PHASE TRANSITIONS IN HIGH RESISTIVITY BATIO3 SINGLE CRYSTALS

We have observed that (i) in some high resistivity BaTiO3 crystals the cubic-tetragonal phase transition is of the Wechsler-Lieberman-Read type, contrary to theoretical predictions, and (ii) high resistivity BaTiO 3 crystals have a stable domain structure which is the same as that which is associated with a martensitic transformation. Our interpretation of (i) is that, because of (ii), when the phase boundary lies in a suitable orientation a plane of zero average distortion is formed and a martensitic transformation results. At all other orientations the phase boundary is broad to accommodate the elastic strain and the transition is not of the austenite-martensite type, as expected.