Sol-gel derived cobalt doped LaCrO3: Structure and physical properties

Abstract

Nanocrystalline samples of LaCr1-xCoxO3 (0 ≤ x ≤ 0.3), synthesized through the sol-gel process are characterized to investigate the effect of cobalt doping on various physical properties. The orthorhombic structure of the samples is verified by the XRD patterns. Lattice parameters are estimated using PowderX software and are found to follow the Vegard's law. Williamson Hall analysis is employed to compute the crystallite size and lattice strain. Crystallite sizes exhibit a decrease whereas lattice strain shows an overall increasing trend with the increase in Co concentration. The random dispersal of grains is recognized through scanning electron micrographs and the EDX analysis approves the purity of the samples. TEM analysis provides the particle size in the range of 10–30 nm. The presence of characteristic band in FTIR spectra confirms the formation of LaCr1-xCoxO3 (0 ≤ x ≤ 0.3) samples. UV/Visible analysis is used to calculate the energy band gap and other optical parameters and cobalt doping decreases the band gap considerably. Thermal analysis reveals the occurrence of structural transition for all the samples. Imaginary part of dielectric permittivity and loss tangent decrease with increase in the frequency and finally becomes constant at higher frequencies. The AC conductivity data obey the Jonscher's universal dynamic law and it is established that small polaron hopping is involved in the conduction mechanism. Electrical modulus increases with the rise in frequency indicating the short range mobility of charge carriers. Nyquist plots exhibit only one incomplete and distorted semi-circular plots for all the samples specifying that the relaxation process deviate from the ideal Debye type behaviour. Also, both the grains and charge carriers hopping give rise to the conduction phenomenon in these orthochromites.