Colossal dielectric constant and extremely low loss in T-type La2CuO4−δ ceramics

In this paper, we present the colossal dielectric behavior of T-type La2CuO4-δ (LCO) ceramics synthesized in fine grained form using wet chemical “Pechini” process, followed by annealing in argon (Ar) atmosphere. The colossal dielectric constant (CDC) (103≤εr′≤104) displayed over a wide frequency (1 Hz ≤f ≤ 1 MHz) and temperature (−100–150 °C) ranges was equally complimented by the remarkably low dielectric losses (0.01≤ tan δ≤0.1) for LCO ceramics, which are the lowest reported dielectric losses for the T-type La2CuO4 system, so far. This substantial decrease in losses could be attributed to the enhanced resistivity (108−109 Ω.cm) of the sample. Further, the origin of CDC, in this non-ferroelectric LCO, was investigated using combined ac impedance and modulus spectroscopy. The study revealed heterogeneity in electrical microstructure of LCO, with semiconducting grains and insulating grain boundaries. This electrically heterogeneous microstructure could give rise to the Internal Barrier Layer Capacitance (IBLC) mechanism, thus leading to apparent CDC in LCO.