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Synthesis, structural analysis and electrical properties of La 1-x Sr x Ga 1-y Mg y o 3-δ(0.1≤x,y≤0.3) powdersKioupis D., Gaki A., Kakali G.*TUE-5POS69National Technical University of Athens, School of Chemical Engineering, Athens, Greece.*kakali@central.ntua.grThe compounds La 1-x Sr x Ga 1-y Mg y O 3-δ (LSGM) are of great scientific and technological interest, due to theirsuperior oxygen-ion-conducting properties. These compounds belong to the ABO 3 (A: rare earth, B: transitionmetal) perovskite group and are considered as promising materials for the substitution of Yttria StabilizedZirconia (YSZ) electrolytes in Solid Oxide Fuel Cells (SOFCs) [1-3].The subject of this work is the synthesis of pure La 1-x Sr x Ga 1-y Mg y O 3-δ (0.1 ≤x,y≤ 0.3), the refinement of theircrystal structure, the measurement of specific electrical properties and the correlation of the stoichiometry withtheir structure and properties.All compounds were prepared via a polymeric precursor route and the effect of stoichiometry on precursor’sstructure and morphology as well as on properties were studied. Citric acid and ethylene glycol are used aschelating and complexing agents respectively. Microwave heating is used for the preparation of the precursorsand is also tested for their final sintering. The intermediate and final products were examined by means of X-rayDiffraction (XRD), infrared Spectroscopy (FTIR) and scanning electron microscopy (SEM). The unit cell, theatomic positions and the length and angle of chemical bonds were determined by means of Rietveld structurerefinement. Finally, ionic conductivity was measured.As it is concluded, pure La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3-δ can be prepared through the modified Pechini route aftercalcination at 1300 o C for 6 h. This temperature is lower than that reported in the literature [4].La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3-δ , La 0.9 Sr 0.1 Ga 0.9 Mg 0.1 O 3-δ and La 0.9 Sr 0.1 Ga 0.7 Mg 0.3 O 3-δ contain traces of secondary phasessuch as SrLaGa 3 O 7 and SrLaGaO 4 . Particularly, La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3-δ and La 0.9 Sr 0.1 Ga 0.9 Mg 0.1 O 3-δ contain 4.3and 6.8 % SrLaGa 3 O 7 , respectively, while La 0.9 Sr 0.1 Ga 0.7 Mg 0.3 O 3-δ contain 9.8 % SrLaGaO 4 . The stoichiometryseems to have a major effect on the structure of the precursors, dissociation of the polymeric network as well asthe structure of final products and the amount of secondary phaces.Rietveld structure refinement led to the determination of the crystallographic parameters, the representationof perovskite unit cells as well as the determination of the movement pathways of oxide ions into the perovskitelattice. The average size of crystallites of the final products found to be under 100 nm as it was estimated byScherrer equation. Table 1 presents the refined crystallographic parameters.La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3-δ seems to consist of a combination of cubic and monoclinic phases. The main phase(80% by weight) has a monoclinic distortion with space group I12/A1. The secondary phase is cubic with spaceogroup Pm 3 m. In the monoclinic phase, the GaO 6 octahedra are tilted around a and c axis. The final products ofLa 0.9 Sr 0.1 Ga 0.9 Mg 0.1 O 3-δ , La 0.9 Sr 0.1 Ga 0.7 Mg 0.3 O 3-δ and La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3-δ at 1300°C appears to have the cubicostructure with space group Pm 3 m. Unit cell of both phases are shown in Figure 1.Fig. 1. Unit cell of monoclinic (left) and cubic (right) structure of La 1-x Sr x Ga 1-y Mg y O 3-δ (0.1 ≤x,y≤ 0.3).265