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.

Dielectric spectroscopy analysis of the high permittivity (κ∼104) copper (II) oxide (CuO) ceramic shows that the grain contribution plays a major role for the giant-κ value at low temperature, whereas grain boundary (GB) contribution dominates around room temperature and above. Moreover, impedance spectroscopy analysis reveals electrically heterogeneous microstructure in CuO consisting of semiconducting grains and insulating GBs. Finally, the giant dielectric phenomenon exhibited by CuO is attributed to the internal barrier layer (due to GB) capacitance mechanism.

KxTiyNi1−x−yO(x = 0.05–0.3, y = 0.02–0.25) ceramics (abbreviated as KTNO) have been synthesized showing high permittivity. All the KTNO samples of varying compositions exhibit high dielectric permittivity (∼104) near room temperature, which is comparable to that of the recently discovered CaCu3Ti4O12 (CCTO) ceramic. The high dielectric constant of KTNO depends on both the K and Ti content and can be attributed to the Maxwell–Wagner polarization mechanism and to a thermally activated mechanism.

Magnetic nanocrystalline Gd2O3 particles have been successfully synthesized in a silica glass matrix by the sol–gel method at calcination temperatures of 700 °C and above. The optical spectra, corresponding to the transition from ground 8S7/2 to the excited 6P, 6I and 6D multiplets, show a large blue shift which increases with decreasing particle size. Calculated free ion parameters represent different electrostatic and spin–orbit interactions of nanocrystalline Gd2O3 compared with the bulk Gd2O3. The thermal behaviour of magnetization (zero-field-cooled and field-cooled) and magnetic hysteresis of Gd2O3 nanocrystals in the 5–300 K temperature interval have demonstrated that the Gd2O3 nanocrystals present in these glasses display superparamagnetic–ferromagnetic transition at low temperatures. The present Gd2O3 nanoparticles embedded in the silica glass matrix show a high (∼103) dielectric constant with considerable low loss and good temperature-independent character associated with an important technological implication which promises wide applications in memory devices.

The KxTiyNi1−x−yO system in the series AxTiyNi1−x−yO (A=Li, K, Na; x=0.05–0.30, y=0.02) shows the highest dielectric constant ε′∼105 and lowest loss. The high ε′ value is attributed to microstructures, which form boundary layer capacitors. Electrical conductivity in these materials follows small polaron hopping mechanism in the nonadiabatic regime. Unlike LixTiyNi1−x−yO and NaxTiyNi1−x−yO (NTNO), KxTiyNi1−x−yO (KTNO) exhibits an anomaly around Tp∼430K. Tp shifts to the lower temperature range with increasing K content which is related to the higher ionic radius of K.