• V S Saji

      Articles written in Bulletin of Materials Science

    • Compatibility of RuO2 electrodes with PZT ceramics

      K T Jacob G Rajitha V S Saji

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      Because of its high electrical conductivity and good diffusion barrier properties ruthenium dioxide (RuO2) is a good electrode material for use with ferroelectric lead zirconate–titanate (PZT) solid solutions. Under certain conditions, RuO2 can react with PZT to form lead ruthenate (Pb2Ru2O6.5) during processing at elevated temperatures resulting in lead depletion from PZT. The standard Gibbs energies of formation of RuO2 and Pb2Ru2O6.5 and activities of components of the PZT solid solution have been determined recently. Using this data along with older thermodynamic information on PbZrO3 and PbTiO3, the stability domain of Pb2Ru2O6.5 is computed as a function of PZT composition, temperature and oxygen partial pressure in the gas phase. The results show PbZrO3-rich compositions are more prone to react with RuO2 at all temperatures. Increasing temperature and decreasing oxygen partial pressure suppress the reaction. Graphically displayed are the reaction zones as a function of oxygen partial pressure and PZT composition at temperatures 973, 1173 and 1373 K.

    • Thermal expansion of doped lanthanum gallates

      K T Jacob S Jain V S Saji P V K Srikanth

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      Thermal expansion of several compositions of Sr and Mg-doped LaGaO3 including an 𝐴-site deficient composition (La0.9Sr0.1)0.98(Ga0.8Mg0.2)O2.821 were measured in the temperature range from 298 to 1273 K. The effect of doping on thermal expansion was studied by varying the composition at one site of the perovskite structure (either 𝐴 or 𝐵), while keeping the composition at the other site invariant. Thermal expansion varied nonlinearly with temperature and exhibited an inflexion between 550 and 620 K, probably related to the change in crystal structure from orthorhombic to rhombohedral. The dependence of average thermal expansion coefficient (𝛼av) on the dopant concentration on either 𝐴 or 𝐵 site of the perovskite structure was found to be linear, when the composition at the other site was kept constant. Mg doping on the 𝐵-site had a greater effect on the average thermal expansion coefficient than Sr doping on the 𝐴-site. Cation deficiency at the 𝐴-site decreases thermal expansion when compositions at both sites are held constant.

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