K. Narasimha Reddy

A.c. conductivity and dielectric studies of silver-based fast ion conducting glass system

Abstract Different dopant salt (AgI) compositions in the AgI–Ag 2 O–SeO 2 –V 2 O 5 (SSV) system were prepared by the melt quenching technique. All the prepared compositions of the SSV system were characterized by X-ray diffraction, IR and DSC. The electrical conductivity measurements were made on the various dopant salt contents of SSV glasses at 1 KHz as well as a function of frequency (5 Hz to 13 MHz) and temperature (295–323 K). The true bulk conductivity ( σ e =2.61×10 −2 S/cm) and the electrical behavior (equivalent circuit) of the SSV glassy system were obtained from impedance analysis. The variation of conductivity with the AgI content in the SSV system was explained using the diffusion path model. Also, frequency dependence of dielectric constant ( ϵ ) and conductivity ( σ ) were calculated using the impedance data, obtained for the various AgI contents of the SSV system. The variation of dielectric constant and conductivity with the frequency were explained by correlating the microscopic nature of the ionic conduction process in the SSV system.

A new Na+ ion conducting polymer electrolyte based on (PEO+NaYF4) and its use as an electrochemical cell

Abstract Poly (ethylene oxide) (PEO) based solid polymer electrolyte with NaYF4 salt has been prepared and investigated by IR, optical absorption and transport number measurements. The material is found to be a mixed (ionic + electronic) conductor. An electrochemical cell with the configuration Na/PEO+NaYF4/(I2+C+ electrolyte) has been prepared and studied its characteristics for which the open circuit voltage (OCV) and short circuit current (SCC) are 2.4 V and 8υA respectively. A number of cell parameters evaluated are also reported.

Thermoluminescence characteristics of Sm3+ doped NaYF4 crystals

Thermoluminescence (TL) characteristics of NaYF4 crystals doped with Sm3+ have been studied after γ-ray irradiation. Dependence of luminescence efficiency on Sm3+ concentration and radiation dose has been measured and possible applications of NaYF4: Sm3+ as a novel phosphor for TL dosimetry have been investigated. The efficiency of 0·3 mole% Sm3+ doped NaYF4 crystal has been found to be maximum and comparable with commercial thermoluminescence dosimetric (TLD) materials.

Pre- and post-irradiation deformation effects on the thermoluminescence of KCl:Y crystals

Abstract The thermoluminescence (TL) behaviour of X-irradiated KCl crystals containing yttrium have been investigated as a function of plastic deformation, both prior to and subsequent to irradiation. In the crystals subjected to deformation prior to irradiation, the TL intensity is found to increase with the amount of plastic deformation whereas in those subjected to deformation subsequent to irradiation, the same is observed to decrease. A new high temperature glow peak is also found to grow due to the plastic deformation before irradiation. These results are explained on the basis of various processes of point and line defect interactions; such as creation, modification and annihilation of traps by moving dislocations, etc.; that take place during the plastic deformation of the crystal.

Complex admittance study of potassium yttrium fluoride

Abstract The complex admittance of pure and 0.5 mol% sodium doped potassium yttrium fluoride polycrystalline pellets, between two inert blocking electrodes, was studied from 300 to 950 K in the frequency range 50–100 kHz. In most cases the admittance plot exhibited a depressed circular arc in the low frequency region and a straight line in the high frequency region. The bulk conductivity σ, the dielectric constant e′ and the loss angle tan δ were determined from the admittance plots. The high values of e′ observed at high temperatures were attributed to space charge polarization effects. The a.c. conductivity was found to increase with increasing frequency.

Thermoluminescence in KCl crystals containing yttrium

Abstract Thermoluminescence (TL) of X-irradiated KCl single crystals containing different concentrations of yttrium is studied in the temperature range 30–250 °C, in which the TL intensity is found to decrease with increasing yttrium concentration. In all the yttrium-doped KCl crystals, the TL glow curves show three glow peaks: T 1 peak (85–100 °C), T 2 peak (115–120 °C) and T 3 peak (160–180 °C). Annealing of the irradiated crystals doped with 1 mol.% yttrium shows the elimination of the T 1 peak whereas the F-bleaching of the irradiated crystal at room temperature increases the intensity of the T 2 peak while decreasing the intensities of the other glow peaks. From these observations, the T 1 peak is attributed to background impurities, the T 2 peak to yttrium-related centres and the T 3 peak to F-centres. The trap depths corresponding to these glow peaks are calculated using various peak methods.

Thermally stimulated discharge currents in potassium yttrium fluoride

Abstract Thermally stimulated discharge currents of potassium yttrium fluoride pellets have been studied as a function of polarizing temperature and polarizing field strength at a constant heating rate of 0.09 K s −1 . The activation energies, relaxation parameters and charge were evaluated. The origin of the thermally stimulated discharge current (TSDC) peak was attributed to the space charge process.

Ionic conductivity in samarium-doped NaCl

A study of ionic conductivity as a function of temperature has been carried out in NaCl and NaCl doped with 0.5 and 1.0 mol% samarium. The conductivity-temperature plot of NaCl exhibits a well-known three-stage conductivity in the temperature range 100 to 650° C. The knee separating intrinsic and extrinsic regions is at a temperature of about 525° C. The conductivity-temperature plots of samarium-doped NaCl exhibit three-stage extrinsic (II, III and IV) conductivity in the temperature range 100 to 525° C. The intrinsic region I, was not observed in these plots, as the conductivity measurements were taken up to 525° C. From the analysis of these plots activation energies for the migration of cation vacancy, the formation of Schottky pairs, the association of the samarium ion with a cation vacancy and the dilution of samarium ions in the lattice of NaCl are calculated. These values are compared with previously reported ones.

On photoacoustic spectra of X-irradiated NaCl : Y crystals

Abstract A correlation between the photoacoustic (PA) and optical absorption (OA) spectra of X-irradiated NaCl:Y crystals is reported. The F-band spectra observed through PA spectroscopy is found to be sharper than that of OA spectroscopy. This sharpening is attributed to the reduced probability of nonradiative decay processess of F-Centres over the radiative processes. Two bands observed in the UV region of both the spectra are attributed to the Y + impurity transitions in the host matrix.

Growth of highly transparent and conductive CdO thin films deposited at different thicknesses by RF reactive magnetron sputtering

Cadmium oxide (CdO) thin films were deposited on glass substrates by RF reactive magnetron sputtering using pure cadmium target in a mixture of argon and oxygen gases. The effect of film thickness on the structural, surface morphological, optical and electrical properties of CdO films was systematically investigated by X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, atomic force microscopy, UV-visible spectrophotometer and Hall effect measurements. X-ray diffraction (XRD) studies showed that the films were polycrystalline in nature with a preferential orientation along (2 0 0) plane. Atomic force microscopy studies showed that these films were very smooth with maximum root mean square roughness of 3·64 nm. The CdO films formed at film thickness of 300 nm exhibited optical transmittance of 82%, electrical resistivity of 1·6×10−3 Ω cm and figure of merit of 2·5×10−3 Ω−1.Abstract Cadmium oxide (CdO) thin films were deposited on glass substrates by RF reactive magnetron sputtering using pure cadmium target in a mixture of argon and oxygen gases. The effect of film thickness on the structural, surface morphological, optical and electrical properties of CdO films was systematically investigated by X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, atomic force microscopy, UV-visible spectrophotometer and Hall effect measurements. X-ray diffraction (XRD) studies showed that the films were polycrystalline in nature with a preferential orientation along (2 0 0) plane. Atomic force microscopy studies showed that these films were very smooth with maximum root mean square roughness of 3·64 nm. The CdO films formed at film thickness of 300 nm exhibited optical transmittance of 82%, electrical resistivity of 1·6×10−3 Ω cm and figure of merit of 2·5×10−3 Ω−1.