Chandkiram Gautam

A Review on Infrared Spectroscopy of Borate Glasses with Effects of Different Additives

Borate glasses are the technologically important class of glasses and play a significant role in various applications. Borate glasses contain planar BO3 groups as structural units, rather than tetrahedral SiO4 groups. The oxygen atoms are, as in SiO2, again connected to two network-forming atoms, in case of boron. The radial distribution analysis describes the B2O3 glass structure as consisting of boroxol rings, that is, planar rings containing three boron atoms and three oxygen atoms. The network forming of the B2O3 and the SiO4 is affected with the addition of some metal cation additives Pb, Zn, Cd, and so forth. These additives also work as a network modifier and a nucleating agent for crystallization of glass. Therefore, the optical properties of the borate glasses have been changed significantly.

Dielectric behavior of perovskite glass ceramics

The recent developments of energy storage devices are concerned with larger energy storage ability, low loss and good temperature stability. It has a great technological importance in engineering science. The dielectric materials like ceramics and glass ceramics have great interest in electronic ceramic industry due to above concern. The ceramic dielectrics are used as a capacitive element in electronic circuits. The perovskite glass ceramics have very high dielectric constant and low dielectric loss. The high dielectric constant in glass ceramics is attributed to space charge polarization. In order to produce glass ceramics of high dielectric constant, barium titanate glass ceramics is the first discovered ferroelectric perovskite. In this review article, we are summarizing the dielectric behavior of perovskite glass ceramics such as BaTiO3, SrTiO3, PbTiO3, (Ba,Sr)TiO3 and (Pb,Sr)TiO3.

Synthesis of Low-Density, Carbon-Doped, Porous Hexagonal Boron Nitride Solids.

Here, we report the scalable synthesis and characterization of low-density, porous, three-dimensional (3D) solids consisting of two-dimensional (2D) hexagonal boron nitride (h-BN) sheets. The structures are synthesized using bottom-up, low-temperature (∼300 °C), solid-state reaction of melamine and boric acid giving rise to porous and mechanically stable interconnected h-BN layers. A layered 3D structure forms due to the formation of h-BN, and significant improvements in the mechanical properties were observed over a range of temperatures, compared to graphene oxide or reduced graphene oxide foams. A theoretical model based on Density Functional Theory (DFT) is proposed for the formation of h-BN architectures. The material shows excellent, recyclable absorption capacity for oils and organic solvents.

Zirconia based dental ceramics: structure, mechanical properties, biocompatibility and applications

Zirconia (ZrO2) based dental ceramics have been considered to be advantageous materials with adequate mechanical properties for the manufacturing of medical devices. Due to its very high compression strength of 2000 MPa, ZrO2 can resist differing mechanical environments. During the crack propagation on the application of stress on the surface of ZrO2, a crystalline modification diminishes the propagation of cracks. In addition, zirconias biocompatibility has been studied in vivo, leading to the observation of no adverse response upon the insertion of ZrO2 samples into the bone or muscle. In vitro experimentation has exhibited the absence of mutations and good viability of cells cultured on this material leading to the use of ZrO2 in the manufacturing of hip head prostheses. The mechanical properties of zirconia fixed partial dentures (FPDs) have proven to be superior to other ceramic/composite restorations and hence leading to their significant applications in implant supported rehabilitations. Recent developments were focused on the synthesis of zirconia based dental materials. More recently, zirconia has been introduced in prosthetic dentistry for the fabrication of crowns and fixed partial dentures in combination with computer aided design/computer aided manufacturing (CAD/CAM) techniques. This systematic review covers the results of past as well as recent scientific studies on the properties of zirconia based ceramics such as their specific compositions, microstructures, mechanical strength, biocompatibility and other applications in dentistry.

Structural and crystallization behavior of (Ba,Sr)TiO3 borosilicate glasses

Various glass samples were prepared by melt quench technique in the glass system [(Ba1− x Sr x ) TiO3]–[2SiO2–B2O3]–[K2O] doped with 1 mole% of La2O3. Infrared spectra show the number of absorption peaks with different spliting in the wave number range from 450 to 4000 cm−1. Absorption peaks occurs due to asymetric vibrational streching of borate by relaxation of the bond B–O of trigonal BO3. Raman spectra show the Raman bands due to ring-type metaborate anions, symmetric breathing vibrations BO3 triangles replaced by BO4 tetrahedra, and symmetric breathing vibrations of six-member rings. The differential thermal analysis of a glass sample corresponding to composition x = 0.0 shows crystallization temperature at 847°C and glass transition temperature at 688°C. X-ray diffraction (XRD) pattern of glass ceramic samples shows the major crystalline phase of BaTiO3 whereas pyrochlore phases of barium titanium silicate. Scanning electron micrographs confirm the results of XRD as barium titanate is major crystalline phase along with pyrochlore phase of barium titanium silicate.

Crystallization and dielectric properties of Fe2O3 doped barium strontium titanate borosilicate glass

An attempt has been made to prepare barium strontium titanate borosilicate glasses in the system, 64[(Ba1−xSrx)·TiO3]–30[2SiO2·B2O3]–5[K2O]–1[Fe2O3] (0.4 ≤ x ≤ 1.0), using the conventional melt-quench method. The prepared glasses were characterized by differential thermal analysis, X-ray diffraction, scanning electron microscopy and impedance spectroscopy techniques. On the basis of the DTA results, the glasses were crystallized via regulated heat treatment process. The activation energy for crystallization was 818 ± 1.6 kJ mol−1. A high dielectric constant of about 107 070 was obtained for the 6 hour heat treated glass ceramic sample. Fe2O3 plays an important role in enhancing crystallization, dielectric constant and retardation of dielectric loss in the samples.

Enhanced supercapacitor performance of a 3D architecture tailored using atomically thin rGO–MoS2 2D sheets

A 3D architecture is fabricated using 2D nano-sheets of GO and MoS2 as the building blocks by a facile, one-pot chronoamperometry method to achieve a conductive additive free, binder free and scalable supercapacitor electrode. The superior electrochemical properties of the 3D PPy-rGO–MoS2 (PGMo) are due to its porous structure, thin wall, high surface area and high electrical conductivity that endow rapid transportation of electrolyte ions and electrons throughout the electrode matrix. The synergistic effect between the components in a proper ratio improves the supercapacitor performance and material stability of PGMo. The possible correlation of the structure and electrochemical performance of the 3D ternary composite is backed by a fully atomistic molecular dynamics (MD) simulation study. The high specific capacitance (387 F g−1) and impressive cycling stability (>1000 cycles) estimated for PGMo open up an opportunity to consider the 3D ternary nanostructures as cutting edge materials for energy storage solutions.

Crystallization Behavior and Microstructural Analysis of Strontium Rich (PbSr−)TiO Glass Ceramics in Presence of LaO

Crystallization and microstructural behavior of various strontium-rich glass ceramics in the system 65[(PbxSr1−x)TiO3]-24[2SiO2⋅B2O3]-5[BaO]-5[K2O]-1[La2O3] (0.0≤𝑥≤0.4) with addition of 1% La2O3 have been investigated. The addition of La2O3 has been found to play an important role in crystallization of perovskite (Pb,Sr)TiO3 as a solid solution phase. Also, it causes a change in the surface morphology of the fined crystallites of the major phase. Differential thermal analysis (DTA) shows only one exothermic crystallization peak, which shifts towards higher temperature with increasing amount of strontium oxide. Glasses were subjected to various heat treatment schedules for the crystallization. Very good crystallization of strontium-rich glass compositions is observed. X-ray diffraction studies confirm that cubic perovskite lead strontium titanate crystallizes as major phase. Lattice parameter decreases with increasing strontium content similar to lead strontium titanate ceramics. Uniform and interconnected crystallites are dispersed in glassy matrix.

Synthesis, Structural and Optical Studies of Barium Strontium Titanate Borosilicate Glasses Doped with Ferric Oxide

Various barium strontium titanate borosilicate glasses were prepared by a rapid melt-quench technique. Spectroscopic studies have been carried out on investigated glasses for their structural information. Infrared and Raman spectroscopic studies showed that these glasses are formed by glass-forming network of borate and silicate as well as network modifiers in the form of cations of alkaline earth atoms. The borate and silicate networks are modified by barium, strontium, titanium, and iron cations in glass matrix. The network of triborate unit is modified in tetraborate unit by adding ferric oxide in a glassy matrix. The optical studies are performed by ultraviolet-visible spectroscopy and it confirms that the band gap decreases with increase in the concentration of ferric oxide.

Synthesis and Structural Properties of Lead Strontium Titanate Borosilicate Glasses with Addition of Chromium Trioxide and Graphene Nanoplatlets

Various lead strontium titanate borosilicate glass samples were prepared with addition of 1 mol % of chromium trioxide and graphene nanoplatelets by convention melt quench method. Their structural and optical behaviors were studied by infrared spectroscopy, ultraviolet–visible spectroscopy, and scanning electron microscopy. The infrared spectroscopic studies were carried in the wavenumber range of 400–4000 cm−1. The energy band gap of bulk transparent glass samples were found by Tauc plots of ultraviolet–visible spectra. Surface morphological studied was done by scanning electron microscopy. The density of these prepared lead strontium titanate borosilicate glass samples were calculated by “Archimedes principle” of liquid displacement method.