Investigation of Structural, Optical and Electrical Transport Properties of Yttrium Doped La0.7Ca0.3MnO3 Perovskites

Abstract

In the present study, bulk samples of yttrium doped La0.7−xYxCa0.3MnO3 (x = 0.3 and 0.4) are prepared through solid-state reaction route. The structural, optical and electrical transport properties have been explored through various analytical techniques. The x-ray diffraction (XRD) patterns affirm single phase and polycrystalline nature of the samples. Rietveld refinement analysis of the XRD data is used to determine the various structural parameters. It reveals that both the samples belong to orthorhombic crystal system with Pnma space group. Using Scherrer’s equation, a lower value of crystallite size is found in the higher concentration of yttrium doped sample. The band gap as determined from the UV–visible DRS data by employing the Tauc’s relation is found to enhance with the increase of yttrium concentration in La0.7Ca0.3MnO3. The low temperature resistivity measurements establish semiconducting nature of the samples over the temperature range of ~ 110–300 K. Moreover, the electrical resistivity data are interpreted within the variable range hopping (VRH) model to estimate the density of states at the Fermi level N(EF), mean hopping distance Rh(T) and hopping energy Eh(T). It is observed that the electrical quantities vary gradually with the change of Y content. The conduction mechanism in this system is governed in the framework of thermally activated small polaron hopping (SPH) model and accordingly various parameters namely Debye temperature (θD), activation energy (Ep) and optical phonon frequency (νph) are evaluated. The obtained results support a strong connection between structure and electrical behavior in our samples and can be elucidated on the basis of localization of charge carriers induced by the substituting ions.