ABSTRACT
We investigated the low-frequency dielectric properties of a Pb(3)Mn(7)O(15) single crystal with manganese ions in the mixed-valence state (Mn(3+)/Mn(4+)). Dielectric relaxation was found in the frequency window from 20 to 100 kHz in the temperature range 110-180 K. The dielectric spectra of the crystal were analyzed using a Debye model. Estimations made within the model and analysis of resistivity data suggest that the relaxation behavior of the dielectric constant is related to polaronic charge carrier hopping. Around 250 K, charge ordering occurs in the crystal when the Mn(3+) and Mn(4+) ions are arranged in a specific order among the crystal sites. With a decrease in temperature, an ac electric field can induce a charge hop between the equivalent lattice sites available, related to crystal symmetry. This hopping is equivalent to the reorientation of an electric dipole that yields Debye-type behavior of the complex dielectric constant. The observed anisotropy in the behavior of the dielectric properties and resistivity can be attributed to a pronounced two-dimensional character of the crystal structure.
Subject(s)
Cations/chemistry , Lead/chemistry , Manganese Compounds/chemistry , Oxides/chemistry , Crystallization/methods , Electric Conductivity , Electronics , Models, Chemical , TemperatureABSTRACT
The current report is devoted to the further study of magnetic properties of MnGeO(3) single crystals with orthorhombic symmetry Pbca. New data from magnetic measurements in magnetic fields up to 80 kOe are presented. A spin flop transition is observed at H(sf) = 35 kOe and T = 4.2 K along the a-axis. The exchange and anisotropy fields are determined. The magnetic structure of MnGeO(3) with T(N)≈36 K is qualitatively described using a two-sublattice model.
