Crystal structure, thermal expansion, electrical conductivity and chemical compatibility studies of nanocrystalline Ln_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ) (Ln = Nd, Sm,Gd)

摘要

Nanocrystalline pcrovskite oxide based cathode materials Ln_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ) (Ln = Nd, Sm, Gd) (LnSCF) has been synthesized by gel-combustion method using glycine as a fuel. The decomposition and crystallization behavior of precursor was studied by TG/DTA analysis. The detection and identification of impurities in the powders obtained after combustion was done by FTIR spectroscopy. Crystal structure, thermal expansion, electrical conductivity of composition Ln_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ) (Ln = Nd, Sm, Gd) were studied as a function of temperature. X-Ray diffraction study shows that phase pure pcrovskite structure with orthorhoinbic symmetry is obtained after calcinations at 1173 K, except in the case of Gd_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ) (GdSCF) in which cubic phase is also present besides the orthorhoinbic phase. The average crystallite sizes of samples were obtained by Scherrcr's equation and were found to be between 18-23 nm. Linear thermal expansion coefficient (TEC) of these cathode materials was determined by dilatometry technique. The composition Nd_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ) (NdSCF) shows the lowest TEC value. The dependence of the electrical conductivity on temperature was measured from room temperature to 1173 K using four probe method. Nd_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ) shows the maximum electrical conductivity followed by Sm_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ) (SmSCF). Morphological analysis of the powder calcined at higher temperatures was studied by scanning electron microscope (SEM). The chemical compatibility of these cathode materials has been studied with the electrolyte material Ln_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ) (LSGM) prepared by gel-combustion method.