Kamal Singh

Electrical conductivity of Li2O-B2O3-Bi2O3: a mixed conductor

Abstract The transport properties of the glassy Li 2 O-B 2 O 3 -Bi 2 O 3 system, prepared in three different series-I, -II and -III characterized by X-ray powder diffraction, IR, DSC and SEM analyses have been investigated for their ionic and electronic nature using complex impedance and Wagners d.c. polarization techniques respectively. Glasses of series-I and -II are found to be ionic, whereas those of series-III, are partially electronic. Electronic contribution increases with the increased concentration of bismuth at the cost of boron. The occurrence of two overlapping semicircles in the complex impedance plane in the case of the samples of series-III, has been discussed in the light of two relaxation times due to the presence of Li-B and Li-Bi glassy phases.

Ag+ glass-Ag2SO4 composite solid electrolyte based SO2 galvanic sensor

Abstract The ionic conductivity of 10Ag2O:30SiO2:60B2O3 glass dispersed Ag2SO4 composite solid electrolyte system, prepared by liquid phase sintering, is investigated in the temperature range from 773 to 573 K. The maximum conductivity, 2×10−3 S cm−1 (at 573 K) is achieved on 30 wt.xa0% glass addition to Ag2SO4. The enhancement in such electrolyte systems is discussed in the light of high conducting space charge layer, formed across heterojunction (glass–crystal interface). Galvanic SO2 gas sensor using optimised composite electrolyte with Ag+Ag2SO4 solid reference is found to be more stable against long term use and thermal shocks, compared to the sensor based on pure crystalline solid electrolyte.

SO x 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.

A comparative study on the processing, dielectric and electrical properties of PMN based solid solutions

Lead magnesium niobate (PMN) based binary with lead titanate (PT), lead iron niobate (PFN) and lead zinc niobate (PZN) and ternary with PZN-PT and PFN-PT solid solutions have been synthesized. In depth characterization using X-ray diffraction and SEM techniques have revealed the major perovskite phase formation. Amongst all the solid solutions, PMN-PZN-PT has given the highest values of permittivity as 19,740 and 23,700 withTc as 34°C when sintered at 1080°C and 1180°C respectively on the one hand and on the other, PFN containing solid solutions exhibited distinct deviation from the relaxor behaviour.

Ion conductivity commensurate with lattice distortion in Ag2SO4

Abstract The ionic conductivity of (1 − x )Ag 2 SO 4 ( x )M 2 SO 4 (where x = 0 to 0.07 and M = Li , Na, K, Rb and Cs) has been systematically investigated by using complex impedance spectroscopy. The solid solubility limits up to 3 mol% of M 2 SO 4 in β-Ag 2 SO 4 has been set with X-ray powder diffraction and scanning electron microscopy techniques. The transport number obtained at different temperatures using Wagners d.c. polarization method shows negligible electronic contribution. The conductivity behaviour appears to be strongly dependent on the magnitude of difference in ionic radii of host and guest. The lattice structure related term has been correlated to ionic conductivity to explain the results.

Effect of preparative parameters on the formation of perovskite pmn ceramic

Relative permittivity measurements performed on the perovskite lead magnesium niobate (PMN) ceramic synthesized by the conventional (M-I) and Swartzs (M-II) methods in the light of preparative parameters like calcination and sintering conditions along with the addition of excess PbO and MgO are reported. The results suggest that the relative permittivity exhibits a maximum for the specimen having uniform distribution of fine pyrochlore (PMNC) grains of size <0.6 microns in the matrix of PMN. In addition to this, it is also found that the method M-II is superior to M-I. The formation of PMN is found to be critical to the excess PbO and MgO in case of M-I and M-II respectively.

Synthesis and characterization of Ag2SO4–ABO3 (A=Li/Ba and B=Nb/Ti) heterogeneous solid electrolyte systems

Abstract The ionic conductivity of Ag2SO4:BaTiO3 and Ag2SO4:LiNbO3 composite solid electrolyte systems are investigated using complex impedance spectroscopy. More than an order of magnitude enhancement in the ionic conductivity is achieved in case of 70Ag2SO4:30LiNbO3 compared to pure Ag2SO4. A surface charge transfer mechanism is suggested to understand the microscopic conduction process. The highest conducting (1.82×10−3 (S cm−1) at 250°C) composition is found to be promising for SOx electrochemical gas sensor application.

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.

PC based instrument for impedance analysis, cyclic voltammetry and transient analysis

A low cost PC based instrument for low frequency impedance measurements and analysis has been designed, fabricated and tested. A software program has been implemented to generate the equivalent circuit from the impedance measurements. The same set-up can also be used for time domain techniques like cyclic voltammetry and transient studies.

Investigation of Nano Size Lead Magnesium Niobate Synthesised by Combustion Method

Lead magnesium Niobate, Pb(Mg 1/3 Nb 2/3 )O 3, samples prepared by combustion method with diffrent percentage of fuel, are found to exhibit high sintered density with low particle size (in nano range). A considerable reduction in the concentration of unwanted pyrochlore is achieved by following the combustion method. The temperature dependent XRD study in the range 200–800°C suggests a linear lattice expansion with α a = 2 × 10 − 6 nm/°C. 100% excess urea as fuel during combustion synthesis gives material with highest room temperature relative permittivity (7080) with low dissipation loss (0.04) vis-à-vis other. The enhanced relative permittivity is due to nano-particles of PMN confirmed by X-ray powder diffraction and scanning electron microscopy.