The complex dielectric properties for ceramic samples of TbMnO3 were investigated as functions of temperature (100K⩽T⩽360K) and frequency (100Hz⩽f⩽100kHz). Two thermally activated dielectric relaxations were found with the activation energies of 0.30 and 0.22eV for the high- and low-temperature relaxations, respectively. By means of complex impedance analysis the high-temperature relaxation was identified to originate from the internal barrier-layer capacitor effects related to the grain boundaries, and the low-temperature relaxation was ascribed to the dipolar effects induced by charge-carrier-hopping motions inside the grains.

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Low-frequency (100Hz⩽f⩽1MHz) dielectric properties of La0.8Sr0.2MnO3∕Nb-doped SrTiO3 heterojunctions were investigated in detail at room temperature. Negative capacitance was observed at low frequencies under positive dc biases. This phenomenon was found to result from the combinational contributions from the Maxwell–Wagner interfacial relaxation and the dipolar relaxation related to detrapped carriers which give rise to inductive effect under an applied electric field.

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