Thesis (M.Sc.)--Chulalongkorn University, 2007

The perovskite–like oxides Ln(Pr, La)₂₋ₓSrₓMO₄ (M = Co, Ni, Cu) (x = 0.4, 0.6, 0.8, 1) were synthesized by the modified citrate method in order to study the influence of strontium doping at A–site on the structure and property. As the results, characterized by XRD supported by FT–IR and SEM, all specimens can be prepared and showed homogeneous K₂NiF₄–phase but Ln(Pr, La) ₂₋ₓSrxCoO₄ series had physical instability. The substitution of Sr²⁺ (larger radius) for Pr³⁺ or La³⁺ (smaller radius), caused the transformation of structure from orthorhombic to tetragonal. Moreover, doping with strontium affected on the decreasing of melting points of the materials, resulting in enhanced grain growth according to the density. However, Cu also can affect the decreasing of the melting point of Ln(Pr, La) ₂₋ₓSrₓCuO₄, so the fusion of grain of cuprates more easily occurred than that of nickelates. The electrical conductivity can be improved by addition Sr at A–site. The conductivities of the nickelate were higher than that of cuprate. PrSrNiO4 showed the highest electrical conductivity (423.5 S/cm at 300 ℃) which was about 4 times higher than that of undoped Pr₂NiO₄ (107.4 S/cm at 400 ℃) and LaSrNiO₄ showed the electrical conductivity of 361.6 S/cm at 400 ℃ which was about 4.5 times higher than that of La₂NiO₄ (80.1 S/cm at 400 ℃). The higher electrical conductivity of PrSrNiO₄ combined with higher oxygen adsorption indicate that this material could be a good candidate for use in solid oxide fuel cell.