IBLC effect leading to colossal dielectric constant in layered structured Eu2CuO4 ceramic

Dielectric (εr′) studies of phase pure T′-type Eu2CuO4 ceramics of two markedly different grain sizes (D), prepared by (i) conventional powder mixing and (ii) citrate complexation-Pechini process, have been carried out in the frequency range 0.1 Hz to 1 MHz, and at temperatures −100 °C to 150 °C. εr′ is found to be highly grain size dependent. For the sample with coarse bar-like grains (D2~17×6 μm2) εr′ is >103, and for the finer grain size sample with bimodal distribution (D1~1 μm, D2~3 μm) εr′ is ~105; for both the samples, high εr′ value is nearly frequency independent over 500 Hz≤f<100 kHz and T≥30 °C. The impedance spectroscopy (IS) study has clearly shown that both, the coarse- and the fine-grained samples consist of semiconducting grains and insulating grain boundaries that primarily lead to an internal barrier layer capacitance (IBLC) effect. And thus, manifest colossal dielectric constant (εr′>103) in Eu2CuO4 ceramics. The smaller grain size (Pechini) sample, with over an order higher number of grains and grain boundary network, showing over an order higher εr′ (~105) compared to the coarse grained one, further endorses the IBLC effect.