Large dielectric permittivity in the paraelectric RMn2O5 with R=Tb, dy, and er

The complex dielectric permittivities (epsilon('),epsilon('')) of RMn2O5 (R=Tb, Dy, and Er) are measured in the temperature range of 78-328 K with frequencies ranging from 100 Hz to 1 MHz. A large real part of the dielectric constant epsilon(') (40-140) is observed at room temperature in all three samples studied. These values are higher than the peak value found at the ferroelectric transition of RMn2O5 single crystals. Our results reveal that high dielectric permittivities are related to thermally activated dipolar motions with activation energies of similar to 300 meV and a relaxation frequency of similar to 3x10(12) Hz. The possible relation between the high dielectric permittivity and the size effect of R ions based on the spin-phonon interaction is suggested. (c) 2008 American Institute of Physics.