Characteristic of spontaneous polarization in Pb5Ge3O11 crystals

The temperature behavior of the spontaneous polarization of lead tetragermanate, a uniaxial ferroelectric, is studied in the range from 4.2 to 300 K. The results obtained along with the data from the literature make it possible to reconstruct a complete pattern of the behavior of P-s(T) both in the vicinity of the phase transition and at lower temperatures. In the range from 290 K to T-c, the crystal behavior is found to change from the dipole type (beta = 1/2) to the pseudoquadrupole type (beta = 1/4). This specific crossover manifests itself in the change in the behavior of P-s(1/beta) as a function of (T-C-T). In the low-temperature range, weak anomalies in the dependence P-s(T) are found, which point to the occurrence of contributions from the dipole moments of separate structural fragments of Ge2O7 and GeO4, Which have internal degrees of freedom and are weakly bound to the dynamics of the crystal lattice. (C) 2005 Pleiades Publishing, Inc.