Ferrielectric behaviors in Li₂Ge₇O₁₅ crystals

Abstract

Temperature dependence of spontaneous polarization P₅ (T) in ferroelectric Li₂Ge₇O₁₅ crystals has been measured in a wide range of temperature from 300 K to 15 K by a pyroelectric charge method. Temperature dependence of dielectric constant ε (T) has precisely been measured in the paraelectric phase. It is shown that the experimental results can be explained by a ferrielectric model, in which two kinds of nonequivalent antiparallel sublattice polarizations are induced by a soft phonon mode having negligibly small oscillator strength.