• S S Bhoga

Articles written in Bulletin of Materials Science

• Aliovalent substitution inβ-Li2SO4 towards conductivity enhancement

Aliovalent sulphates were selected for substitution in β-Li2SO4 at 6% vacancy concentration. The results show that if the guest ions are substituted on the basis of the criteria given for the formation of a solid solution, then it is possible to achieve a considerable enhancement in conductivity especially in the case of isostructural materials.

• An analysis of the electrical conductivity of the Ag2SO4-K2SO4 binary system

Electrical conductivity of the Ag2SO4-K2SO4 binary system shows three maxima at 20, 70 and 90 mole% of K2SO4 added to Ag2SO4. The first and the third maxima have been explained in the light of intragrain percolation due to lattice distortion, whereas, the second maximum by the surface percolation. The limit of solid solubility has been set at 20 mole% on the basis of evidences obtained from XRD, DTA and SEM techniques.

• An analysis of the electrical conductivity in BaSO4-added Ag2SO4 solid electrolyte system

The compositions (1 −x)Ag2SO4−(x)BaSO4, wherex=0·01 to 0·6, were prepared by slow cooling of the melt. The extent of the solid solubility of Ba2+ in Ag2SO4 was determined by X-ray powder diffraction and scanning electron microscopy. The bulk conductivity of each sample was obtained using a detailed impedance analysis. The partial substitution of Ba2+ results in the enhancement of conductivity in compliance with the classical aliovalent doping theory. A simplistic model based on lattice distortion (expansion) due to partial substitution of Ag+ by the bigger Ba2+ has been considered to explain enhanced conductivity. Beyond solid-solubility limit (5·27 mole%) the BaSO4-dispersed Ag2SO4 conductivity follows the usual trend seen in binary systems. An increase in conductivity in this case is discussed in the light of interfacial reactions and surface defect chemistry. The maximum conductivity in 20 mole% BaSO4 dispersed Ag2SO4 is due to percolation threshold.

• Effect of stoichiometry on the thermal expansion coefficients of lithium niobate single crystals

The chemical analysis of LiNbO3 single crystals, with different melt compositions (Li/Nb)m=0·945, 1·0, 1·1 and 1·2, grown by slow cooling technique, reveals a remarkable difference in solid and melt compositions. The thermal expansion coefficients alonga andc axes, determined by using Newton’s ring experiment, are found to increase anisotropically with increase in (Li/Nb)m ratio. The variation in thermal expansion coefficient with increase in the (Li/Nb)m ratio is discussed in the light of defect chemistry i.e. the partial replacement of Li+ by excess Nb5+ creates additional cation vacancies to attain the electro-neutrality in the crystal.

• SOx solid state gas sensors: A review

The performance of any solid state electrochemical gas sensor is always rated on its response time, thermodynamic stability, operating temperature, gas sensing ability, sensitivity and gas concentration range which is sensed. Here, we have reviewed the factors contributing towards a gradual development of electrochemical solid state SOx sensor in terms of a continuous tailoring of its two basic components, i.e. solid electrolyte and reference electrode with high ionic and mixed (ionic + electronic) conductivities, respectively.

• # Bulletin of Materials Science

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Volume 42 | Issue 6
December 2019

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