Fundamental material property trends in the La0.8-xNdxCa0.2FeO3-delta series: crystal structure and thermal expansion

摘要

Compounds from the series La0.8-xNdxCa0.2FeO3-delta (0.1 <= x <= 0.7) were synthesised by a sol-gel route. X-ray diffraction and Rietveld analysis showed that materials with 0 <= x <= 0.6 crystallize as single-phase orthorhombic perovskites. The smaller ionic radius of Nd3+ compared to La3+ leads to a decrease in unit cell volume with increasing x. Elemental mapping by high-resolution scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy confirms the homogeneous distribution of the A-site elements (La, Nd and Ca) in the perovskite (ABO(3)) lattice. The thermal expansion behaviour of La0.8-xNdxCa0.2FeO3-delta (0 <= x <= 0.6) was characterized by dilatometry at 30 <= T/degrees C <= 1000 and 1 x 10(-3) <= pO(2)/bar <= 1. The thermal expansion coefficients of La0.8-xNdxCa0.2FeO3-delta, which were determined in regions I (40-530 degrees C) and II (530-990 degrees C), respectively, are almost independent of the Nd concentration in the range of (0 <= x <= 0.6) and increase slightly with decreasing pO(2). The transition from orthorhombic to trigonal modification, which is observed for La0.8Ca0.2FeO3-delta at approx. 740 degrees C, is suppressed for all Nd-substituted compounds with x >= 0.1.