Synthesis, structural and ferromagnetic properties of La_1−x K _x MnO₃ (0·0 ≤ x ≤ 0·25) phases by solution combustion method

Abstract

We describe the solution combustion synthesis and characterization of La_1–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 La_0·85K_0·15MnO₃ 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.