Sanjib Bhattacharya

Structural and Optical Properties of V2O5-MoO3-ZnO Glass-Nanocomposite System

ABSTRACT The present work points to highlight the physical, structural and the optical properties of some semiconducting V2O5-MoO3-ZnO glass-nanocomposites using density, molar volume, X-ray diffraction (XRD), field effect scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and UV-VIS absorption spectra. We have observed that addition of V2O5 increases (or decreases) the density (or molar volume) of the glassy system due to structural changes. Distribution of Zn3V2MoO11, Zn2.5VMoO8 and Zn2V2O7 nanoparticles has been confirmed from FESEM and XRD studies. It has been observed from FTIR spectra that the network structure depends upon isolated strongly deformed M oO4 polyhedra and VO4 metavanadate chains. Vibrations of MoO6 octahedra, Zn2V2O6, Zn2V2O7, Zn3V2MoO11 and VO2 are observed from the Raman spectroscopic studies. The fundamental UV-VIS absorption spectra have been analyzed, which indicates indirect transitions. GRAPHICAL ABSTRACT

Positron annihilation studies and complementary experimental characterization of xAg2O–(1 − x)(0.3CdO–0.7MoO3) metal oxide glass nanocomposites

Metal oxide nanocomposites of the composition xAg2O–(1 − x)(0.3CdO–0.7MoO3) were prepared by a melt-quenching method and were characterized by different experimental techniques like X-ray diffraction, high resolution transmission electron microscopy and optical absorption spectroscopy. X-ray diffraction showed sharp diffraction peaks indicating large crystallites but transmission electron microscope images also showed crystallites of nanometer dimensions in appreciable concentrations, which confirmed the nanocomposite structure of the samples. Although the lattice constants did not show significant changes with the increase in concentration (x) of Ag2O, there is considerable relaxation of the growth-induced strain above x = 0.2. Interestingly this is also the concentration above which the optical band gap energy showed a mild decrease. One salient feature of this study is the use of positron annihilation spectroscopy for identifying and monitoring the structural defects such as vacancies and vacancy clusters as well as the free volume cavities during the change in concentration of Ag2O. Positron lifetime measurements indicated trapping of positrons initially in the interfacial defects within the 0.3CdO–0.7MoO3 nanocrystalline ensemble and then in the free volume defects within the amorphous Ag2O matrix. At higher Ag2O concentrations, positron trapping appeared to take place within the Cd2+-monovacancies in CdO and in the divacancies of neighbouring cationic and oxygen monovacancies in the α-MoO3 and CdMoO4 nanocrystallites. At x = 0.1–0.2, the effective positron trapping centres are translocated to the tetrahedral Mo6+-monovacancies instead of the Cd2+-monovacancies. The results of coincidence Doppler broadening spectroscopic measurements, which map the electron momentum distribution and its variations, indicated increasing trapping of positrons with increasing concentration of Ag2O, which again is attributed to the trapping sites in the increasing number of nanocrystallites being formed.

Electrical Transport of Mixed Phased Glassy Nanocomposites

Ionic conductivity and conductivity relaxation of ZnO doped silver molybdate glass-nanocomposite systems have been studied. X-ray diffraction studies have been carried out to obtain the particle size and the distribution of ZnO, Ag2MoO4, Ag2Mo2O7 and Ag6Mo10O33 nanoparticles dispersed in glass-nanocomposites. A symmetric stretching of the Mo–O octahedral units has been found in the FTIR study. It has also been noted that as ZnO content increases, the bond strength of Mo–O becomes weaker. Ionic relaxation data of glass-nanocomposites have been analyzed in the framework of the electric modulus formalism. It has been observed that the electrical conductivity depends upon the ZnO content added to the system.

On the mechanical properties of selenite glass nanocomposites

In this paper the room temperature micro-hardness of selenite glass-nanocomposites has been measured using a Vickers and Knoop micro hardness tester where the applied load varies from 0.01N to 0.98 N. A significant indentation size effect was observed for each sample at relatively low indentation test loads. The classical Meyer’s law and the proportional specimen resistance model were used to analyze the micro-hardness behavior. It was found that the selenite glass-nanocomposite becomes harder with increasing CuI composition and the work hardening coefficient and mechanical properties like Young modulus, E, were also calculated. Our results open the way for the preparation, application and investigation of significant mechanical properties of new type of glass-nanocomposites.

V 2 O 5 -MoO 3 -ZnO thick film resistors as highly selective trace level ethanol gas sensors

The Glass nanocomposite materials in the form of fine granular powders were synthesized by conventional melt quenching technique. Thick films of the synthesized powders were fabricated by screen printing technique, followed by firing at 100oC, for 2 hours. Upon exposure to 50 ppm ethanol gas, due to oxidation or reduction reaction at the surface of the as prepared nanocomposite materials with the target gas, exchange of electrons take place thereby affecting the sensors resistance greatly leading to drastic change in conductance. The glass nanocomposite of composition xV2O5-(1−x) (0.05MoO3-0.95ZnO) where x = 0.95 (sample-C) was observed to most sensitive to ethanol at room temperature. The surface misfits, operating temperature, gas concentrations, etc. affect the microstructure and gas sensing performance of the sensing element. The quick response and fast recovery are the main features of this sensor. The microstructure of the as prepared glass nanocomposites was analyzed to study the gas response and selectivity of the sensor in the presence of ethanol and some other gases also.

Electrical and mechanical properties of ZnO doped silver-molybdate glass-nanocomposite system

Zno doped silver-molybdate glass-nanocomposites, 0.3 Ag2O - 0.7 [0.075 ZnO – 0.925 MoO3] have been prepared by melt-quenching method. Ionic conductivity of these glass-nanocomposites has been measured in wide temperature and frequency windows. Vicker’s hardness methods have been employed to study micro-hardness of the as-prepared samples. Heat-treated counterparts for this glass-nanocomposites system has been analyzed in different temperature to observe the changes in conductivity as well as micro-hardness for that system.

Relaxation of Cu+2 in selenite glass nanocomposites

The present study mainly focuses on the electrical relaxation data of some glass-nanocomposites. We have prepared xCuI- (1-x)(0.5CuO - 0.5SeO2) where x = 0.2 and 0.5 using melt-quenching method. Ionic relaxation data of these glass-nanocomposites have been analyzed in the framework of the electric modulus formalism. Conductivity relaxation frequency (τc) has been computed from the maximum value (M//max) of the imaginary modulus M//. It is also observed that the conductivity relaxation process is highly non-exponential. The variation of conductivity relaxation time is correlated with their structure.