Lightly doping Ca2+ in perovskite PrCoO3 for tailored spin states and electrical properties

Abstract

A series of Pr_1−xCa_xCoO₃ samples were prepared using a novel molten salt reaction that is convenient to obtain single phases avoiding aggregates compared to conventional solid state reactions. The formation reaction was monitored by X-ray diffraction combined with thermal analysis, and all samples were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and alternating current impedance. It is demonstrated that all Pr_1−xCa_xCoO₃ samples crystallized in a pure orthorhombic perovskite structure. By increasing the doping level, the symmetry of the orthorhombic structure was enhanced, and is followed by an increase in the population of Co³⁺ in the intermediate spin state. All samples exhibited typical semiconducting behavior, showing conductivities highly dependent on the Ca²⁺ doping. The conduction for x = 0 shows a simple thermal activated process, which changed into a Mott's variable range hopping mechanism for x > 0. By increasing the Ca²⁺ doping level, the relevant activation energy is decreased, while the density of the localized electronic state is increased.