Ac conductivity and dielectric properties of CuFe1−xCrxO2 : Mg delafossite

Abstract

The electrical and dielectric properties of CuFe1−xCrxO2 (0 ⩽ x ⩽ 1) powders, doped with 3% of Mg and prepared by solid-state reaction, were studied by broadband dielectric spectroscopy in the temperature range from −100 to 150 °C. The frequency-dependent electrical and dielectric data have been discussed in the framework of a power law conductivity and complex impedance and dielectric modulus. At room temperature, the ac conductivity behaviour is characteristic of the charge transport in CuFe1−xCrxO2 powders. The substitution of Fe3+ by Cr3+ results in an increase in dc conductivity and a decrease in the Cu+–Cu+ distance. Dc conductivity, characteristic onset frequency and Havriliak–Negami characteristics relaxation times are thermally activated above −40 °C for x = 0.835. The associated activation energies obtained from dc and ac conductivity and from impedance and modulus losses are similar and show that CuFe1−xCrxO2 delafossite powders satisfy the BNN relation. Dc and ac conductivities have the same transport mechanism, namely thermally activated nearest neighbour hopping and tunnelling hopping above and below −40 °C, respectively.