The Effect of Barium Non-Stoichiometry on the Phase Structure, Sintering and Electrical Conductivity of BaZr0.7Pr0.1Y0.2O3
AuthorsMohamed Shibly, Kaamil
KAUST DepartmentPhysical Sciences and Engineering (PSE) Division
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AbstractThis thesis attempts to test the effects of barium non stoichiometry and varying calcination temperatures on the microstructure and electrical conductivity of BaxZr0.7Pr0.1Y0.2O3- δ (x = 0.9, 1.0, 1.1). BZPY powders were fabricated using a combustion method, with the quantity of barium carefully controlled to create powders with a 10% molar excess or deficiency of barium. Then, portions of the precursor were calcined at 900 ºC, 1000 ºC, 1100 ºC, 1200 ºC and 1300 ºC for 5 h. The resulting calcined powders were pressed into pellets and sintered at 1600 ºC for 10 h, in a powder bath of the same chemical composition. In all, three chemically different powders were synthesized, and each composition was subjected to five different calcination temperatures, resulting in fifteen different samples to characterise. The precursor from the combustion method was characterised by using an STA to perform both TG and DSC simultaneously. The chemical composition of the precursor and calcined samples was analysed using ICP-OES. XRD was used to characterise the phases of both the powders and the sintered pellets. Lattice parameter indexing using Topaz and Scherrer's equation were used to extract the lattice parameters and crystallite sizes respectively. The microstructure of the pellets was examined using an SEM, the grain size measured using a linear intercept method and pore size using ImageJ. Finally, EIS was used to measure the conductivity of the pellets in dry and wet Argon atmospheres, with silver electrodes. Unfortunately, neither changes to barium stoichiometry nor partial calcination could improve the performance of BZPY. Partially calcined samples did not give rise to dense pellets, barium deficient samples showed inferior conductivity and barium excess samples, while showing higher conductivity than the barium deficient pellets at high temperature, were fragile and had to be handled carefully. Ultimately, the attempt to improve the performance of BZPY did not succeed and alternate methods of improving the grain growth need to be sought.