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Single crystals of LiNbO3 are grown by the flux method. Measurements are made in the temperature range 20 to 1170 °C of the dielectric constant ϵ, dielectric loss and relative thermal expansion ΔLl/l along the polar axis (the three‐fold axis x3) and perpendicular to the glide plane (x1). A sharp maximum in ϵ corresponding to a decrease in volume is observed in the x3 direction at 1140 °C. This temperature is assumed to be the Curie temperature of LiNbO3 which corresponds to the transition from an electrically ordered state (ferro or ferrielectric, rather than antiferroelectric) into a paraelectrical state. The temperature dependences of ϵ and Δl/l below the Curie temperature show several similar anomalies. Some of these anomalies may be due to phase transitions.

and Physico-Technical Ioffe-Institute, Academy of Science8 of the USSR, Leningrad Field-induced Phase Transition in Lead Magnesium Niobate Dedicated to Professor 0. BRUMMER on the occasion of his 60th birthdayThe temperature dependence of the dielectric constant, polarization, and elastic compliance as well as the field dependence of the polarization and strain at different temperatures was measured a t lead magnesium niobate single crystals for three different directions. From the results some conclusions with respect to the symmetry of the field-induced ferroelectric phases can be drawn. Below -7 0 "C and after complete poling, the spontaneous polarization is probably directed along [ l l l ] .An Bleimagnesiumniobat-Einkristallen wurden die Temperaturabhiingigkeit der Dielektrizitatskonstanten, der Polarisation und der elastischen Nachgiebigkeit sowie die Feldstkrkeabhiingigkeit der Polarisation und der Dehnung bei verschiedenen Temperaturen gemessen, und zwar bei drei verschiedenen Beldrichtungcn. Die Ergebnisse ermoglichen einige Aussagen bezuglich der Symmetrie der feldinduzierten ferroelektrischen Phasen. Unterhalb -70 "C und nach vollstandiger Polung ist die Richtung der spontanen Polarisation wahrscheinlich parallel [lll].

The dielectric properties, birefringence, domain structure, electrooptic and pyroelectric effects, specific heat and electroacoustic echo have been investigated in Cd2Nb2O7 at successive phase transitions. Physical properties in different phases have been discussed. The thermoactivated reorientations of polarization at the diffuse phase transition temperatures contribute not only to ε, electrooptic and pyroelectric effects, but also influence the electroacoustic echo relaxation time due to the spectral diffusion mechanism.

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