M. Vithal

Optical and electrical properties of PbO-TiO2, PbO-TeO2, and PbO-CdO glass systems

The optical and electrical properties of the lead bearing glasses in the PbO-TiO2, PbO-TeO2, and PbO-CdO systems have been investigated. The density, refractive index, optical band-gap, and Urbach energies of these glasses are reported. It is shown that the additive nature of oxide ion polarizabilities reported for the simple oxides can be extended to glass systems as well. A modified linear relationship between (Eopt)1/2 and 1−(Rm/Vm) holds good for glasses. The oxide ion polarizabilities deduced from two different experimental quantities viz., refractive index and optical band-gap energy agree well. The dc electrical conductivities have been measured in the temperature range 350–700 K. The activation energies are close to 1 eV. The low melting 70PbO-30TeO2 glass shows higher isothermal conductivity compared to other glasses of similar composition. In PbO-TiO2 glass the PbO content contributes significantly to conductivity and composition dependence of pre-exponential factor (σ0) supports tunneling mecha...

Synthesis, Characterization and Photocatalytic Activity of KAl0.33W1.67O6 and Sn0.5Al0.33W1.67O6xH2O

Nano sized defect pyrochlore, KAl0.33W1.67O6 (KAW), is prepared through sol–gel method. Divalent tin‐doped KAW is obtained at room temperature by ion exchange method using acidified SnCl2 and parent KAW. These materials are characterized by powder X‐ray diffraction, thermogravimetric analysis (TGA), scanning electron microscopy—energy dispersive spectra (SEM‐EDS), Raman Spectroscopy and X‐ray photo electronic spectroscopy. The composition of tin‐doped KAW is obtained from chemical analysis, SEM‐EDS and TGA methods and written as Sn0.5Al0.33W1.67O6 xH2O (x = 1.4–1.5) (SnAW). It crystallizes in cubic lattice with Fd3¯m space group. The band gap energies are found to be 2.82 and 2.21 eV for KAW and SnAW respectively. The observed reduction in the band gap with the introduction of Sn2+ in defect pyrochlore lattice is due to mixing of 5s state of Sn2+ with O 2p states leading to an upward shift in the valence band. The Raman spectra of these materials gave more bands than the number expected for defect pyrochlores due to substitutional disorder in 16c sites and displacive disorder of A ions. The photoactivity of SnAW is higher compared to KAW.

Metathesis synthesis, characterization, spectral and photoactivity studies of Ln2/3MoO4 (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er and Y)

Abstract Rare earth ortho-oxomolybdates of composition Ln2/3MoO4 (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er and Y) were prepared by metathesis reaction. All these materials were characterized by powder X-ray diffraction, Fourier transform-infrared spectroscopy (FT-IR) and UV-Vis diffuse reflectance spectra. The Rietveld analysis of all the samples was carried out to obtain the unit cell parameters and reliability factors. All the materials were crystallized in tetragonal lattice with I41/a space group. The infrared spectra of all the samples were characterized by bands due to MoO42– units. The bandgap energies of all the samples were obtained from UV-Vis DRS spectra. The luminescence spectra of Ln2/3MoO4 (Ln=Pr, Eu and Dy) showed characteristic transitions of the rare earth ions. The visible light photocatalytic activity of all the samples was studied against degradation of methylene blue.

Preparation, characterization, emission (Eu3+), and electron spin resonance (Gd3+) studies of Y2−xLnxTi2O7 (Ln=Eu and Gd, x=0.0,0.05)

Bulk and nanopyrochlore materials of composition Y2−xLnxTi2O7 (Ln=Eu and Gd, x=0.0,0.05) have been prepared by sol-gel method via peroxo titanium complex precursor. All the samples were characterized by powder x-ray diffraction (XRD), Raman spectra, and transmission electron microscopy (TEM). The unit cell parameters were obtained from Rietveld analysis of XRD patterns. The influence of particle size on the emission of Eu3+ (in Y2−xEuxTi2O7), the electron spin resonance (ESR) of Gd3+ (in Y2−xGdxTi2O7) and optical absorption spectra have been studied. The band gap energy of Y1.95Ln0.05Ti2O7 (Ln=Eu and Gd) was determined and compared with parent Y2Ti2O7. The variation in the emission intensity of Eu3+ is accounted with the particle size and short range order. The spin-Hamiltonian parameters of Gd3+ were obtained from the powder ESR spectra. The single-ion anisotropy was taken in to account in the analysis of powder ESR spectra. The crystallite size was obtained from powder XRD and TEM images.

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 photocatalytic studies of Cu2+, Sn2+ and N3− substituted K5Sb5P2O20

AbstractPotassium antimony phosphates (K-Sb-P-O) exhibit different structural networks and therefore they were studied as photocatalysts in the present investigation. K5Sb5P2O20 was prepared by solid state method. Metal ions (Cu2+ and Sn2+), and non-metal anion, N 3−, were substituted into the K5Sb5P2O20 for possible enhancement of photocatalytic activity. The precursor and substituted compounds were characterized by powder X-ray diffraction, FT-IR, SEM-EDS and UV-Vis diffuse reflectance spectra. Nitrogen substitution into K5Sb5P2O20 lattice was studied by O-N-H and XPS measurements. The photocatalytic activity of all the compounds was studied by degradation of methylene blue and methyl violet. The ion-substituted K5Sb5P2O20 have shown higher photocatalytic activity against both the dyes. The role of reactive intermediate species produced in the photocatalytic reaction was studied using their appropriate scavengers. Graphical AbstractThe red shift observed in the UV-Vis diffuse reflectance spectra of ion (Cu2+, Sn2+ and N3- ) substituted Potassium antimony phosphate (K5Sb5P2O20) indicate the mixing of Cu 3d, Sn 5s and N 2p orbitals with valence band O 2p orbital, which form (Cu 3d + O 2p), (Sn 5s + O 2p) and (N 2p + O 2p) hybrid orbitals, respectively. Higher photocatalytic activity was observed in the ion substituted materials.

Effect of Simultaneous Substitution of Sm and Pr Ions on Dielectric and Ferroelectric Properties of Strontium Bismuth Titanate

Sr Smx Bi(4−x) Ti(4−y) Pry O15 (for x = 0, y = 0 and x = 0.1, y = 0, 0.1 and 0.2 and also for x = 0.2, y = 0.1) ceramics were prepared by Sol-gel Pechni method. Single phase of compounds was confirmed by XRD analysis and Lattice parameters were calculated. Microstructure and chemical analysis were performed using SEM and EDS techniques. The effect of addition of Sm3+ and Pr3+ ions on dielectric and polarization properties of Sr Bi4 Ti4 O15 was studied and shift in transition temperature was observed. The dc conductivity of the samples measured as a function of temperature.

Solid-State Syntheses of Rare-Earth–Doped Sr1-xLn2x/3MgP2O7 (Ln = Gd, Eu, Dy, Sm, Pr, and Nd; x = 0.05) by Metathesis Reactions and their Spectroscopic Characterization

ABSTRACT Rare-earth–doped strontium magnesium diphosphates of composition Sr1-xLn2x/3MgP2O7 (Ln = Gd, Eu, Dy, Sm, Pr, and Nd; x = 0.05) were prepared by metathesis reaction. These diphosphates were characterized by powder X-ray diffraction (XRD), energy dispersive spectra (EDS), and infrared spectroscopy. All these compounds were found to crystallize in monoclinic lattice with P21/n space group. The compositions of all the samples were confirmed from their EDS spectra. The infrared spectra of all the samples were characterized by bands due to units. The 31P MAS-NMR of these compounds suggests the presence of two types of phosphorous ions in the lattice. The electron-spin resonance spectrum of Sr1-xGd2x/3MgP2O7 (x = 0.05) gave “U”-type spectrum due to the low symmetry of the Gd3+ ion in the host lattice. The local symmetry of Eu3+, Dy3+, and Sm3+ in Sr1-xLn2x/3MgP2O7 (Ln = Eu, Dy, and Sm; x = 0.05) was obtained from their room-temperature luminescence spectra.

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...

Enhanced photoactivity of antimony phosphates by substitution of H+, Cu2+ and N3− in the K3Sb3P2O14·xH2O crystal lattice

Abstract Substitutional doping of framework heteroatoms in photocatalysis is one of the approaches for harvesting visible light. Tunnel structure potassium antimony phosphate (K3Sb3P2O14·xH2O) and Cu2+, H+ , and N3- substituted K3Sb3P2O14·xH2O were prepared. These materials were characterized by powder X-ray diffraction, energy dispersive spectra, infrared spectra, and UV–Vis diffuse reflectance spectra. All these compositions were crystallized in the rhombohedral crystal lattice with