LaAl1−xMnxO3 perovskite-type oxide solid solutions: structural, magnetic and electronic properties

Abstract

The structural, magnetic and electronic properties were investigated for LaAl_1−xMn_xO₃ (x = 0.0, 0.005, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0) perovskites prepared by the citrate method and calcined at 1073 K. The materials were characterised by XRD, BET surface area, diffuse reflectance spectroscopy (DRS), magnetic susceptibility measurements and electron paramagnetic resonance (EPR). XRD analysis showed that all the LaAl_1−xMn_xO₃ samples are single phase perovskite-type oxides. A non-linear increase of the unit cell lattice parameters with x was observed. Particle sizes and surface areas were in the range of 270–1200 Å and 4–33 m² g⁻¹, respectively. The oxidation state of manganese in the higher Mn-containing samples was checked by chemical titration, the following Mn⁴⁺/Mn_tot ratios being found: 0.45 for x = 0.4, 0.43 for x = 0.6, 0.49 for x = 0.8, and 0.35 for LaMnO₃. Optical spectra revealed some bands attributable to both Mn⁴⁺ and Mn³⁺ species. A magnetic susceptibility study showed ferromagnetic behavior that decreases with the decrease of x, the high Al-containing materials exhibiting a paramagnetic behavior. Depending on the Mn-content, EPR analysis revealed the occurrence of several Mnⁿ⁺ species: Mn⁴⁺ exchange-coupled by ferromagnetic interaction to nearest neighbor Mn³⁺, Mn⁴⁺ exchange-coupled by antiferromagnetic interaction to near-nearest neighbor Mn³⁺, isolated Mn⁴⁺, isolated Mn²⁺.