M. Raghavender

Durable Unsymmetrical Zinc Phthalocyanine for Near IR Sensitization of Nanocrystalline TiO2 Films with Non-Volatile Redox Electrolytes

We are presenting our results based on unsymmetrical zinc phthalocyanine by adopting ‘push-pull’ concept for the nanocrystalline dye-sensitized solar cells. Using this sensitizer in combination with nonvolatile organic-solvent-based electrolytes, we obtained a photovoltaic efficiency of 1.52% under standard global AM 1.5 sunlight and compared the results with volatile organic-solvent based electrolyte. These devices exhibit admirable stability when subjected to continuous thermal stress at 60 oC for 1000 h. The sensitizer is thermally stable up to 150 oC and can be useful for roof top applications.

Effect of Partial Replacement of Bi on Electrical Properties of Layer Structured Strontium Bismuth Titanate

Bismuth in SrBi 4 Ti 4 O 15 is partially replaced with La 3 + to synthesize SrBi(4 − X)La X Ti 4 O 15 , with x = 0.25,0.5,0.75. The samples have been prepared by sol-gel method using ethylene glycol gel and aqueous solution. This sol-gel process offers some advantages, such as homogeneity and stoichiometry control. The structural characterization of the samples is done using powder X-ray diffraction measurements. The samples are electrically characterized by using dielectric and impedance spectroscopy measurements in the frequency range of 500 Hz to 1 MHz, and temperature range from RT to 600°C. These samples show strong frequency and temperature dependent dielectric relaxations. The power law dependence on a.c conductivity is evaluated. The effect of La 3 + substitution on dielectric, impedance and a.c conductivity is studied. The results obtained are interpreted in terms of the pluckering and on the consequent lattice distortion that is usually present in Bismuth Layer Structured Ferroelectrics.

Preparation, characterization, and impedance studies of LiSbM(PO4)3 (M=Al, Fe, and Cr)

Lithium containing sodium superionic conductors of composition LiSbM(PO4)3 (M=Al, Cr, and Fe) were prepared by solid-state method and were characterized by powder x-ray diffraction and infrared spectroscopy. All compounds were found to crystallize in rhombohedral lattice with space group R3¯c. They show characteristic PO4 vibrational bands. The dc conductivity and ac impedance studies of all these samples correlate well in terms of activation energy of conduction Ea. The Cole-Cole plots do not show any spikes on the lower frequency side, indicating negligible electrode effects. The activation energies obtained from the plots of logσdc vs 1∕T and logσ(0) vs 1∕T are approximately the same suggesting conducting species to be mobile lithium ions. The peak width at half maximum for modulus plots (logf vs M″) is ∼1.34 decades for LiSbM(PO4)3 (M=Al, Cr, and Fe), which is close to 1.14 decades observed for a Debye solid. The heights of M″ obtained from the experimental plots are close to that of M″(max)=C0∕2C, co...

ELECTROMECHANICAL CHARACTERIZATION OF LANTHANUM-DOPED SODIUM BISMUTH TITANATE CERAMICS

The effect of lanthanum doping on the electromechanical properties of lanthanum-doped sodium bismuth titanate was studied. The ferroelectric system under investigation was Na1/2(LaxBi1-x)1/2TiO3 ceramics, with x=0, 0.1, 0.15 and 0.2. Admittance measurements were carried out in the frequency range of 100 Hz to 13 MHz and in the temperature range from room temperature to 550°C. Combined impedance and admittance spectroscopy was used to analyze admittance data. The electromechanical parameters were calculated from the resonant and anti-resonant frequencies obtained from vector admittance plots. The electromechanical coefficients for pure sodium bismuth titanate ceramic samples were found to be much larger than the reported values. Also, it was observed that lanthanum-doping decreased the values of electromechanical coupling coefficients.

Dispersion of relaxation times in impedance measurements of Na1-xKxNbO3 mixed ceramic

Sodium Potassium Niobate ceramic with perovskite structure has been prepared through solid state reaction using conventional double sintering method. The starting materials are mixed in the stoichiometric proportion. The compound is characterized through x-ray diffraction to ensure the formation of single phase. From this data, the lattice parameters are determined. The temperature dependence of the dielectric constant and loss factor are obtained over a wide frequency range. Both dielectric constant and loss factor show two peaks. The dielectric and loss peaks observed at lower temperature are found to be of less intensity. The second dielectric anomaly observed around 430°C is found to follow Curie-Weiss law. The curie constant ‘C’ is observed to be around 10 5 °C. Impedance measurements are also made in the temperature range 30°C to 550°C in frequency range 500 Hz to 1 MHz. Dispersion of impedance with frequency show peaks, which vary both with temperature and frequency. The relaxation times are obtained from these peak frequencies. Activation energy of relaxation is calculated and the results are presented.