High-temperature dielectric behavior of hexagonal HoMnO3

Abstract

The ac electrical response of hexagonal HoMnO3 was investigated in the temperature range 340≤T≤700K. The combination of impedance and electrical modulus spectra reveal a single dielectric relaxation. However, the ac conductivity in the range 340≤T≤600K revealed two electro-active regions with dissimilar activation energies associated with grain and grain boundary regimes. We suggest that grains have the largest capacitance, whereas grain boundary dominates the overall resistance of the sample. The most interesting was the first-hand observation of a positive temperature coefficient of resistance (PTCR) effect in HoMnO3, and the sample behaves as an extrinsic semiconductor material. Both bulk effects and grain boundary were observed to contribute together to the PTCR phenomena. A correlation between the ac conductivity and dielectric data was built up. Results show that oxygen non-stoichiometry and associated electron holes are liable for the complex dielectric behavior. The scaling behavior of ac conductivity was studied using different formalisms.