Structural and Magnetic Characterization of the Series La1-xSrxFe0.8Cr0.2O3-δ (x = 0.2, 0.4, 0.6, and 0.8)

Abstract

A series of perovskite compounds with the general formula La1-xSrxFe0.8Cr0.2O3-δ (x = 0.2, 0.4, 0.6, and 0.8) have been synthesized using a urea/nitrates self-combustion route. Their characterization was performed using room-temperature X-ray diffraction, electrical and magnetization measurements. A structural transition from orthorhombic (x = 0.2) to rhombohedral (x > 0.2) was determined. Among the rhombohedral phases, increased Sr content caused a visible decrease in distortion. Monotonic decreases with increasing x were found for both the pseudocubic lattice parameter (a‘) and <Fe/Cr−O> bond lengths in the 0.2 ≤ x ≤ 0.6 range, which have been attributed to an increase in the mean oxidation state of the transition metals. The lattice expansion observed for x = 0.8, in addition to an apparent stabilization of the <Fe/Cr−O> bond lengths for x = 0.6 and 0.8, suggested an increased role for oxygen vacancy formation as the charge compensation regime for the latter. All compounds exhibited semiconductor behavior with temperature dependencies better described by the 3d variable range hopping model. The monotonic decrease of resistivity with increasing x in the 0.2 ≤ x ≤ 0.6 range was found consistent with an increase in carrier density. The monotony is broken for x = 0.8, which was also associated with the change in the charge compensation regime. Increased x progressively weakened the overall antiparallel coupling of the magnetic moments, inducing a decrease of the ordering temperature for samples in the 0.2 ≤ x ≤ 0.8 range.