BI1-XRXFEO3 (R = RARE-EARTH) - A FAMILY OF NOVEL MAGNETOELECTRICS

Crystals of solid solutions Bi1-xRxFeO3, where R = La, Dy, Gd, were obtained with x less-than-or-equal-to 0.7. Solid solutions of the stated rare earths, as x is increased from 0 to 0.7, have one and the same sequence of five crystal structures (rhombohedral C3v6, triclinic C1(1), orthorhombic D2(6), orthorhombic D2(5), orthorhombic C2v9). The ferroelectric-paraelectric transition occurs in rhombohedral and triclinic crystals at T = 810-560-degrees-C. The high temperature modifications are orthorhombic and cubic. The orthorhombic structure C2v9 holds up to 1180-degrees-C. The ferroelectric domain structure was distinguished in all types of crystals. No magnetoelectric effect (MEE) was detected in the orthorhombic crystals with the D2 (222) symmetry class. But the mm2 crystals were found to have both quadratic and linear MEE. The value of the quadratic effect is considerably smaller than that of the linear one. Magnetoelectric hysteresis takes place in the crystals. The tensorial properties of the obtained crystals are analyzed from the viewpoint of crystal symmetry.