Therefore, the ethylene glycol synthesis route could be a good method for synthesis of LSGM. showed that LSGM powders, which were synthesized by Pechini method, contained 4 – 5 wt % of LaSrGa 3 O 7 /LaSrGaO 4 secondary phases after calcination at 1400 1 C for 8 h. 1 also shows that the LSGM system, sintered at 1350 1 C for 6 h, contains almost no impurity phase. In order to avoid these impurities formed at 1200 1 C, calcination temperature was increased from 1200 1 C to 1300 1 C and it was observed that these secondary phases considerably disappeared. The above impurity phases usually exist along grainboundaries during the synthesis of LSGM and are of low conducting materials compared to LSGM. This was possibly due to the metastable or thermodynamically stable conditions of the secondary phases. Secondary phases LaSrGa 3 O 7 (ICDD 45-0637), LaSrGaO 4 (ICDD 80-1806) and La 4 Ga 2 O 9 (ICDD 53-1108) became more apparent in the sample calcined at 1200 1 C (6 h). The sample, heated at 1100 1 C (for 12 h), contains small amounts of impurity phases like LaSrGa 3 O 7, LaSrGaO 4 and La 4 Ga 2 O 9 along with the main LSGM phase. The phase evolution of LSGM is shown in the XRD patterns of Fig. The development of LSGM phase was studied by recording the XRD patterns of the system calcined at various temperatures. Measurement was carried out in dry air in the temperature range 400 – 800 1 C and in the frequency range 10 À 2 – 10 7 Hz. The impedance data were recorded with the help of Novocontrol impedance analyser. Pt-coated pellet was fi red/ baked at 900 1 C to obtain good adhesion between electrolyte and electrodes. Platinum paint was used for electrodes on both sides of the sintered LSGM pellets for the conductivity measurement. AC impedance spectroscopy technique is well suited for the measurement of electrical conductivities of solid electrolyte materials.
YOBS VS YCAL PC
Dilatometry of the sample was performed in air using a dilatometer DIL 402 PC (NETZSCH, UK) from room temperature to 1000 1 C. Prior to BET analysis, the powders were degassed under vacuum for 6 h at 300 1 C. The speci fi c surface area of calcined powders was estimated by BET method through Micromeritics (ASAP 2020) Accelerated Surface Area and Porosimetry System using adsorption – desorption isotherms of nitrogen.
Relative densities were calculated by measuring the sintered pellet density divided by theoretical density as derived from the lattice parameters. A balance system (Model AX, Mettler-Toledo, Giessen, Germany) was used for determining the density. Density measurements were carried out using the Archimedes principle. SEM image of polished surface of the pellet were recorded with help of Quanta 200 FESEM.
After polishing and thermal etching, the microstructures of the sintered sample were examined by scanning electron microscopy. For phase identi fi cation, the experimental XRD patterns were analyzed by Rietveld re fi nement. Patterns were recorded over the angular range 15 r 2 θ / 1 r 90 with a step size of Δ 2 θ 1⁄4 0.02 1. The crystal structure of the LSGM was identi ed by Rigaku Mini fl ex II desktop powder X-ray diffractometer (XRD) with Ni fi ltered Cu-K α (1.5405 Å) radiation at 30 kV and 20 mA. The details of the characterization techniques are mentioned in the subsequent section. The prepared composition was characterized using various techniques. Thus, this synthesis route produces fi ne powders. This helps in reduction of agglomeration of smaller particles and also the surface of the particles is functionalized.
During the reaction, when nucleation starts, the EG molecules (solvent) surround the smaller particles to form a chemical bond between EG and surface of particle and thus, particle growth is hindered. The oxide powders were dried for 12 h at 100 1 C in a hot air oven. NH 4 OH molecules precipitate La 3 þ, Sr 2 þ, Ga 3 þ and Mg 2 þ ions to their corresponding oxides or/and hydroxides. Decom- position temperature of urea in water medium (120 1 C) is lower than that in gas/solid phase (190 1 C) and it produces NH 4 OH and CO 2. Hydrolysis of urea (NH 2 CONH 2 ) produces NH 4 OH, which acts as precipitating agent. The precipitate of as-synthesized material so obtained was washed three to four times by centrifugation in ethanol to remove the excess of EG. After 5 h of reaction, the solution became light brown. The solution becomes light yellow, indicating the reduction of glycol. The reaction was easily followed through its distinctive color changes. The reaction mixture was heated at 150 1 C for 3 h under re fl ux condition until the precipitation was completed.
0 kommentar(er)
