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Bulk copper (II) oxide (CuO), heat treated at 1223K, shows extraordinarily high dielectric constant (εr∼104), almost independent of temperature (above 230K) and frequency in the kilohertz region. A sudden decrease of εr is observed at lower temperature (below 150K). X-ray photoelectron spectroscopy and high resolution transmission electron microscopy studies confirm the presence of a microscopic amount of Cu3+ in annealed CuO. The dielectric behavior of CuO can be explained by Maxwell-Wagner-type polarization mechanism and thermally activated mechanism.

We report the results of thermoelectric power ͑TEP͒ of a Cr doped La 0.5 Pb 0.5 Mn 1Ϫx Cr x O 3 (xϭ0 -0.45) system measured both in the presence and the absence of magnetic field (Bϭ1.5 T). The small field dependence of the Seebeck coefficient is observed around the metal-semiconductor transition ͑MST͒ temperature (T p ) of the samples. The field dependence of TEP is stronger in the undoped sample. It is noticed from the TEP data that the small polaron hopping conduction mechanism is valid for all these samples ͑for TϾT p ). The polaron radius r p is found to decrease with increase of magnetic field. Low-temperature ͑below T p ) fielddependent and field-independent TEP data can be fitted with SϭS 0 ϩS 3/2 T 3/2 ϩS 4 T 4 suggesting that the electron-magnon scattering strongly affects the low-temperature ͑ferromagnetic phase͒ TEP data of the manganites. Activation energy gradually increases with increasing Cr concentration both in the presence and the absence of magnetic field. Field-dependent thermopower also indicates the importance of spin fluctuations affecting the phonon scattering. Power factor (S 2 /) estimated from the Seebeck coefficient ͑S͒ and resistivity () ͑at zero and 1.5 T field͒ showed a minimum around the MST temperature similar to the field-dependent thermal conductivity data.