Dheeraj Jain

Sm2−xDyxZr2O7 Pyrochlores: Probing Order−Disorder Dynamics and Multifunctionality

The present work involves the synthesis of a series of Sm(2-x)Dy(x)Zr(2)O(7) compounds (0.0 ≤ x ≤ 2.0) by a controlled gel combustion process. The powders were thoroughly analyzed by powder X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy, and diffuse-reflectance UV-visible spectroscopy. The powder XRD studies revealed the system to be single-phasic throughout with retention of pyrochlore-type ordering until 40 mol % of Dy(3+), beyond which the pyrochlore lattice gives way to the defect fluorite structure. Interestingly, Raman spectroscopic studies (as against XRD studies) showed retention of pyrochlore-type ordering throughout the homogeneity range of the compositions studied. This is perhaps the first study that reports retention of a weak pyrochlore-type superstructure in the Dy(2)Zr(2)O(7) system, which was otherwise known to crystallize in the defect fluorite system. The ionic conductivity measurements showed an increase in the activation energy (E(a)) with an increase in the mole percent of Dy(3+) owing to the decreased mobility with an increase in the degree of disorder. The system possesses a tunable band gap with varying amounts of Dy(3+). First-principles calculations were performed to support a decrease in the band gap of the doped system with an increase in the Dy(3+) content. The potential as photocatalysts of some of these compositions was explored, and they exhibited high photocatalytic activity for degradation of xylenol orange, with t(1/2) increasing from pure Sm(2)Zr(2)O(7) to pure Dy(2)Zr(2)O(7).

Polyvinyl alcohol–In2O3 nanocomposite films: synthesis, characterization and gas sensing properties

Poly(vinyl alcohol) (PVA)–In2O3 (with 1 and 5 wt% In2O3 loading) nanocomposite films have been prepared by a solvent-casting technique. The In2O3 nanoparticles used in this work were prepared by nonhydrolytic alcoholysis ester elimination reaction of indium acetate in the presence of oleic acid and oleyl alcohol at 220 °C. X-Ray diffraction (XRD) patterns and transmission electron microscopy (TEM) studies indicate that the In2O3 nanocrystals obtained in this work are nearly monodisperse, highly crystalline with cubic bixbyite structure without the presence of any other impurity phase. The PVA–In2O3 nanocomposite films have been structurally characterized by XRD, Fourier transform infrared (FTIR) and Raman spectroscopy. The results confirm the incorporation of In2O3 nanocrystals in the PVA matrix and interactions between In2O3 nanocrystals and PVA molecules. The thermal properties of nanocomposite films have been investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The thermo-oxidative degradation temperature of PVA increases with the addition of In2O3 nanocrystals and the degree of crystallinity of the PVA matrix decreases in the presence of In2O3 nanocrystals in the nanocomposite films. The room temperature sensing characteristics of the naocomposite films have been studied for various gases, namely, H2S, NH3, CH3, CO, and NO. The PVA–In2O3 nanocomposite films show maximum sensitivity for H2S gas with fast response and reversibility. The response mechanism of the nanocomposite films to various gases is also proposed.

UV-shielding transparent PMMA/In2O3 nanocomposite films based on In2O3 nanoparticles

Self supporting poly(methyl methacrylate) (PMMA)/In2O3 with varying In2O3 content (1, 2, 5 and 10 wt% In2O3 loading) nanocomposite films have been prepared by solvent-casting and spin casting techniques. The nanocomposite films have been structurally characterized by X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy and the results confirm the incorporation of In2O3 nanoparticles in the PMMA matrix. The thermal properties of the nanocomposite films have been investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results show that the degradation of the polymer occurs at higher temperature in the presence of In2O3 nanoparticles and even a small amount of In2O3 nanoparticles (∼1 wt%) can greatly improve the thermal stability of PMMA. The UV-visible spectra of the nanocomposite films show that the films are UV-absorbing, and highly transparent in the visible region.

Tunability of structure from ordered to disordered and its impact on ionic conductivity behavior in the Nd2−yHoyZr2O7 (0.0 ≤ y ≤ 2.0) system

The present paper describes a detailed investigation of the nature of the order–disorder transition in the Nd2−yHoyZr2O7 system, over the entire composition range (0.0 ≤ y ≤ 2.0), using a combination of diffraction and spectroscopic analysis techniques. The complete series of solid solutions has been prepared by the gel combustion technique followed by high temperature sintering. Detailed structural characterization of the prepared samples using X-ray diffraction studies confirmed their single-phase solid solution formation throughout the series, as well as identifying the transformation of the system from an ordered pyrochlore structure (0.0 ≤ y ≤ 0.8) to a disordered fluorite-type structure (0.8 < y ≤ 2.0). Micro-Raman studies further supported the structural information. Micro-structural studies by SEM revealed dense products with uniform grain distribution in these materials. Comprehensive studies were performed to investigate the ionic conductivity behavior of these solid solutions in correlation with the structural transformations using AC impedance spectroscopy. A detailed analysis of ionic conductivity and related parameters, such as activation energies, etc. corresponding to individual conduction mechanisms such as bulk and grain boundary conduction, clearly correlated the effect of structural transformation on these charge transport properties. The composition Nd1.2Ho0.8Zr2O7 with the pyrochlore structure has been found to show the highest ionic conductivity in the entire series, which has been attributed to a combined effect of increasing carrier concentration and their preferred movement through an ordered array of vacant anion sites.

Synthesis and Structural and Electrical Investigations of a Hexagonal Y1–xGdxInO3 (0.0 ≤ x ≤ 1.0) System Obtained via Metastable C-Type Intermediates

Detailed structural and electrical investigations were carried out on an A-site disordered hexagonal Y(1-x)Gd(x)InO3 (0.0 ≤ x ≤ 1.0) series synthesized by a self-assisted gel-combustion route. The phase relations show profound temperature dependence. The metastable C-type modification could be stabilized for all the compositions, which on further heating get converted to stable hexagonal polymorphs. The conversion temperature (C-type to hexagonal) was found to increase with an increase in Y(3+) content. The system was observed to be single-phasic hexagonal at 1250 °C throughout the composition range. Interestingly, the increase in planar bonds of InO5 polyhedra was found to be twice that of the apical bonds on Gd(3+) substitution. Careful Raman spectroscopic studies highlighted a definitive though subtle structural change from x = 0.7 onward. The same observation is also corroborated by the dielectric studies. Electric field-dependent polarization measurements showed the ferroelectric hysteresis loop for pure YInO3. The system transforms from ferroelectric in YInO3 to almost paraelectric for GdInO3. In the present study, XRD, Raman, and electrical characterizations in conjunction reveal that to tune the electrical properties of the hexagonal rare earth indates, the variation in tilting of InO5 polyhedra has to be influenced, which could not be brought about by isovalent A-site substitution.

Corundum type indium oxide nanostructures: ambient pressure synthesis from InOOH, and optical and photocatalytic properties

A simple, cost effective, surfactant free and scalable synthesis of rhombohedral In2O3 (rh-In2O3) nanostructures with controllable size and shape has been developed under ambient pressure by thermal dehydration of InOOH nanostructures. The InOOH nanostructures have been prepared by solvothermal reaction between indium nitrate hydrate with tetramethylammonium hydroxide (TMAH) in anhydrous methanol at 140 °C without any surfactant. The structure and morphology of the nanostructures have been characterized in detail by X-ray powder diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM). The studies reveal that highly crystalline nanostructures of InOOH and rh-In2O3 with rice-grain type morphology are formed. The optical properties of the InOOH and rh-In2O3 nanostructures have been explored by UV-visible diffuse reflectance spectroscopy (UV-DRS) and room-temperature photoluminescence (PL) studies. The direct band gap of as-synthesized InOOH and rh-In2O3 nanostructures was estimated to be 3.75 and 2.95 eV, respectively, from the diffuse reflectance absorbance spectra. Both InOOH and rh-In2O3 nanostructures show intense blue emission under UV excitation which is attributed to the presence of oxygen vacancies. The thermal stability of the rh-In2O3 phase has been studied by differential scanning calorimetry (DSC), differential thermal analysis (DTA) and dilatometry of the as prepared sample. The potential of InOOH and rh-In2O3 nanostructures as photocatalytic materials for hydrogen generation from water/methanol (2 : 1) mixtures under UV/vis irradiation has also been evaluated for the first time.

Chapter 19 – Diamond-Based Radiation Detectors for Applications in Highly Corrosive Solutions and High-Radiation Fields

Abstract Diamond, with its name derived from the Greek word adamas (meaning unconquerable/invincible ), is a unique material with potential use in several applications. In nature, it occurs deep down in the Earths crust in regions of high temperatures and high pressures with limited availability and nonreproducible quality. It is also synthesized industrially using high-temperature, high-pressure methods or chemical vapor deposition (CVD) methods. CVD methods in particular have excellent control over the quality of diamond, and it is possible to synthesize pure/doped diamonds using simple gaseous precursors like H 2 and suitable carbon source (CH 4 , CO 2 , C 2 H 4 , etc.) at low pressures. Both single crystals and polycrystalline diamonds of desired quality can be routinely synthesized. CVD method has therefore brought about a revolution in this field and expanded the development of diamond-based technologies. With its inherent physicochemical properties, diamond is an excellent host matrix for radiation detection purposes. It offers the best performance potential especially under extreme operational conditions such as high temperatures, corrosive environments, intense radiation fields, fast radiation events, etc. CVD diamonds have immense application in this area. The present chapter outlines the potential of CVD diamond as a host matrix for radiation detection under extreme conditions and gives description of diamond-based alpha particle detectors for use in highly corrosive chemical environments, with special reference to estimation of actinides in acidic liquids. Results obtained in our research group on development of such detectors are also summarized. Essential factors that influence performance of diamond-based radiation detectors and possible methods to address them are also detailed.