Activating and modulating ferroelectric and optical properties in La/Nd co-doped SrTiO3 ceramics

Abstract

Defect-dipole and defect-clusters provide a novel paradigm to realize unprecedented dielectric behavior along with ultralow dielectric loss, in any ordinary dielectric material. In the present work, with the help of the La/Nd co-doped SrTiO3 (STO) system, it has been shown that the type, nature, and localization of these defect dipoles and clusters play a significant role in controlling the dielectric behavior. Polycrystalline ceramic samples of La0.1Sr0.9−xNdxTiO3 (x = 0.05, 0.07, 0.09, 0.11) are synthesized by mechanical alloying followed by high temperature solid-state reaction techniques. Investigations of structural and microstructural properties are carried out by using the X-ray diffraction technique and scanning electron microscopy, respectively. The dielectric and electrical parameters are studied in a frequency ranging from 1 kHz to 1 MHz and the temperature ranging from 30 °C to 450 °C. The results demonstrate that all the synthesized samples exhibit single-phase perovskite structure with Pm3̅m space group. Though STO displays quantum paraelectric behavior, intriguingly, all the La/Nd doped STO samples exhibit ferroelectric behavior with the dielectric maximum increasing with the increase in the doping concentration. The superior dielectric behavior in the doped samples is ascribed to the suppression of grain boundary conductivity due to the formation of a double Schottky barrier (due to VSr′′/Vo••) and enhancement of grain conductivity due to localized transport involving defect dipoles/clusters within the grain. Interestingly, the presence of VSr′′andVo•• has been supported by the photoluminescence analysis. Nevertheless, La/Nd doping results in a systematic reduction in the band gap.