Crystal Structure, Magnetic and Electrical Properties of Half-Doped Chromium Manganite La_0.5Sr_0.5Mn_0.5Cr_0.5O₃

Abstract

Polycrystalline sample La_0.5Sr_0.5Mn_0.5Cr_0.5O₃ (LSMCO) was prepared by a conventional solid-state reaction method in the air, and its structure was determined by Rietveld refinement using consistent resolution time-of-flight X-ray diffraction. Different structural models have been used for analysis of X-ray diffraction data recorded at room temperature, but the best fits have been found using a mixture of rhombohedral and an orthorhombic structural phases (42(1)%/57(1)%). The rhombohedral, centro-symmetric space group R$\overline{3}$c$\left(\mathrm{No}.167,a\approx \sqrt{2}{a}_p,c\approx 2\sqrt{3}{a}_p,Z=6\right)$ with octahedral tilting scheme a⁻a⁻a⁻ leading to a three identical out-of-phase tilt angle of (Mn/Cr)-O₆ octahedron along three perovskite main directions: x, y, and z-axes. The orthorhombic space group Pbnm$\left(\mathrm{No}.62,a\approx b\approx \sqrt{2}{a}_p,c\approx 2{a}_p,Z=4\right)$ with octahedral tilting scheme a⁻a⁻c⁺, leads to an anti-phase tilts of the same magnitude about [100] and [010] directions of the elementary specimen cell and in-phase tilt of different magnitude about the [001] direction. At low temperature 10 K, Rietveld refinement of powder diffraction data revealed that the crystal structure of sample is distorted with a single orthorhombic symmetry (space group Pbnm). Magnetic measurements indicate that our investigated sample exhibits an overall anti-ferromagnetic behavior mainly attributed to the frustration induced by both competing AFM Cr³⁺-O-Cr³⁺, Mn⁴⁺-O-Mn⁴⁺ networks, and the mixed one Mn⁴⁺-O-Cr³⁺exchange magnetic interactions. The temperature dependence of the resistivity measured under zero field shows a semi-conducting behavior in the whole temperature range, which probably could be described by the adiabatic small polaron hoping model with relatively high polaron activation energy.