Synthesis, structural and ferromagnetic properties of La1−x K x MnO3 (0·0 ≤ x ≤ 0·25) phases by solution combustion method

Abstract

We describe the solution combustion synthesis and characterization of La1–x K x MnO3 (0·0 ≤ x ≤ 0·25) perovskite phases, which is a low temperature initiated, rapid route to prepare metal oxides. As-synthesized compounds are amorphous in nature; crystallinity was observed on heating at 800°C for 5 min. Structural parameters were determined by the Rietveld refinement method using powder XRD data. Parent LaMnO3 compound crystallizes in the orthorhombic structure (space group Pbnm, No. 62). Potassium substituted compounds were crystallized with rhombohedral symmetry (space group R-3c, No. 167). The ratio of the Mn3+/Mn4+ was determined by the iodometric titration. The Fourier transform infrared spectrum (FT-IR) shows two absorption bands for Mn-O stretching vibration (ν s mode), Mn-O-Mn deformation vibration (ν b mode) around 600 cm−1 and 400 cm−1 for the compositions, x = 0·0, 0·05 and 0·10. Four-probe electrical resistivity measurements reveal a composition controlled metal to insulator transition (T M–I), the maximum T M–I was observed for the composition La0·85K0·15MnO3 at 287 K. Room temperature vibrating sample magnetometer data indicate that for the composition up to x = 0·10, the compounds are paramagnetic whereas composition with x = 0·15, 0·20 and 0·25 show magnetic moments of 27, 29 and 30 emu/g, respectively.