Synthesis, characterization and wide range frequency and temperature dependent electrical modulus study of LaCrO3 and cobalt (Co) doped LaCrO3 perovskite compounds

Abstract

We synthesized the undoped lanthanum chromium oxide, LaCrO3 (LCO), and cobalt (Co) doped LaCr1-xCoxO3 (LCCO), (x = 0.01, 0.10, 0.15, 0.20, 0.30) perovskite compounds using solid-state reaction method. Electrical modulus of the samples was investigated at a wide range frequency and temperature using precision temperature controlled dielectric/impedance spectroscopy in nitrogen ambient. Structural and chemical analyses were carried out using SEM, XRD, FTIR and XPS. SEM images showed that particle sizes are shrinking depend on Co doping ratio. The XRD results revealed that the strongest peak shifts through higher two theta values due to difference ionic radii of Co and Cr. From the FTIR analysis, the bending vibration of O–Cr–O bonding and stretching vibration of Cr–O bonding were observed 600–530 cm-1 and 500–450 cm-1 band regions, respectively. Our XPS studies have exhibited that the oxidation state of Cr is mixed with metallic (0), (3+), (4+) and (6+), Co has (2+) and (3+) oxidation states and La has only (3+) oxidation state. Frequency-dependent real and imaginary part of electrical modulus characteristics were performed for all samples and the results showed that there are two relaxation processes taking place at the grain and grain boundary, for LCO, 1% and 10% Co doped LCO samples. Nonetheless, 15, 20 and 30% Co doped LCO samples demonstrate three relaxation processes, which are due to the dc conductivity, grain and grain boundary. The activation energy of the samples were calculated using log (fmax) & 1000/T plot and the results showed that the activation energy highly depends on the Co doping ratio