Structural and Transport Properties of La_1-xSr_xCo_{1- y-z}Fe_yNi_zO_3-δ Perovskites

Abstract:

The La1-xSrxCo0.2Fe0.6Ni0.2O3-d, La1-xSrxCo0.4Fe0.4Ni0.2O3-d and La1-xSrxCo0.2Fe0.4Ni0.4O3-d perovskites were synthesized with Sr contents 0.1 ≤ x ≤ 0.3 using precursors obtained by citric acid method and their structural and transport properties were measured. All obtained samples crystallize in hexagonal R-3c perovskite structure. The thermal stability was found to decrease with increasing Ni and Sr amounts, what leads to appearance of La2NiO4 like secondary phases with spinel structure and even NiO for higher Ni concentration. The DC electrical conductivity and thermoelectric power measurements at low temperatures (77 – 300K) suggest an appearance of variable hopping mechanism in this temperature range. The transport properties were found to improve with both Sr and Ni concentration increases. The moessbauer spectroscopy studies of La1-xSrxCo0.2Fe0.6Ni0.2O3-d samples revealed presence of two valence states of iron (Fe2+, Fe3+). The measured high temperature (870 – 1070K) DC electrical conductivity is relatively high for samples with high Sr and Ni amounts, what makes them good candidates for a possible application as cathode materials for Intermediate Temperature Solid Oxide Fuel Cells and points to further studies of perovskites from the (La, Sr)(Co, Fe, Ni)O3 system.