Dielectric and Raman spectroscopy study of structural phase transformation of Sr-doped La2CoMnO6 double perovskite

Abstract

Doping at rare earth site by divalent alkaline-earth ions in the double pervoskite system have noticed a variety of magnetic and electronic orders with spatially correlated charge, spin and orbital degree of freedom. In present report, we aim to study the structural, dielectric and magnetic properties of La2−xSrxCoMnO6 $$\left( {x=0,{\text{ }}0.1,{\text{ }}0.3,{\text{ }}0.5} \right)$$ samples synthesized by the solid-state reaction technique. Using powder X-ray diffraction and data analysis with Rietveld refinement a structural identification has been carried out. From high-temperature Raman spectra, a clear structural phase transformation from monoclinic with P21/n symmetry to a rhombohedral phase with R-3 symmetry was evidenced from the softening and an anomalous change in peak widths of both stretching (A1g) and anti-stretching (B1g) modes around 365K. The dielectric measurement is carried out for all the synthesized samples, a sudden change in dielectric constant (e′) and corresponding dielectric loss (tanδ) around 365 K in x = 0, x = 0.1, and x = 0.5 composition samples reflects a remarkable change in the tilts in oxygen octahedra which is because of the structural phase transformation. The susceptibility measurement was also performed to observe the ferromagnetic transitions. In partially ordered undoped and Sr-doped ceramic samples, relaxor-like behavior combined with a large dielectric constant (> 103) is observed. In this paper, successful attempts have been made to observe the structural phase transition through dielectric properties.