P.K. Barhai

Structural, electrical, and optical properties of (Ba1−xNd2x/3)TiO3 ceramics

In this paper, we report the obtention of barium neodymium titanate (Ba1−xNd2x/3)TiO3 ceramics with (0.00 ≤ x ≤ 0.10) by the solid-state reaction method. Structural studies suggested a phase transition from tetragonal to cubic structure with increase in Nd3+ ion content, supported by Rietveld refinement method. Photoluminescence properties revealed that the introduction of Nd3+ ions created structural disorder by means of A-site vacancies and displacement of M–O bond leading to shallow defects. Optical band gap value calculated from ultraviolet–visible spectra decreased with increase in Nd3+ ion concentration. A drastic decrease in grain size of undoped barium titanate was observed with introduction of Nd3+ ions through scanning electron microscopic images. Dielectric properties showed a gradual decrease in the Curie temperature with increase in Nd3+ ion content along with pinching effect. Normal ferroelectric character was obtained within the doping limit. P–E hysteresis loop showed a decrease in remnant polarization and coercive field. However, the composition x = 0.08 and 0.10 showed paraelectric behavior.

Phase formation in selected surface-roughened plasma-nitrided 304 austenite stainless steel

Abstract Direct current (DC) glow discharge plasma nitriding was carried out on three selected surface-roughened AISI 304 stainless steel samples at 833 K under 4 mbar pressures for 24 h in the presence of N2:H2 gas mixtures of 50 : 50 ratios. After plasma nitriding, the phase formation, case depth, surface roughness, and microhardness of a plasma-nitrided layer were evaluated by glancing angle x-ray diffractogram, optical microscope, stylus profilometer, and Vickers microhardness tester techniques. The case depth, surface hardness, and phase formation variations were observed with a variation in initial surface roughness. The diffraction patterns of the plasma-nitrided samples showed the modified intensities of the α and γ phases along with those of the CrN, Fe4N, and Fe3N phases. Hardness and case depth variations were observed with a variation in surface roughness. A maximum hardness of 1058 Hv and a case depth of 95 μm were achieved in least surface-roughened samples.

Diffuse phase transition of BaTi0.6Zr0.4O3 relaxor ferroelectric ceramics

BaTi0.6Zr0.4O3 ceramic was prepared through solid state reaction route. X-ray diffraction showed that the composition has cubic perovskite structure with space group Pm-3m at room temperature. Temperature dependency dielectric study of the ceramic has been investigated. Bulk density was determined using Archimedes principle and found to be ∼97% of X-ray density. The average grain size in the pallet is measured by an optical microscope and found to be 22.23 µm. The dielectric measurement revealed diffuse phase transition of second-order, where dielectric peak temperature (T m) is dependent of frequency showing relaxor-type behaviour. A clear deviation from Curie–Weiss law is observed in the paraelectric region. The dielectric relaxation rate follows the Vogel–Fulcher relation with E a = 0.1020 eV, T f = 106 K, ν0 = 8.5 × 1011 Hz.

Anodic vacuum arc developed nanocrystalline Cu-Ni and Fe-Ni thin film thermocouples

This paper deals with the development of nanocrystalline Cu–Ni and Fe–Ni thin film thermocouples (TFTCs) by using ion-assisted anodic vacuum arc deposition technique. The crystallographic structure and surface morphology of individual layer films have been studied by x-ray diffraction and scanning electron microscopy, respectively. The resistivity, temperature coefficient of resistance, and thermoelectric power of as deposited and annealed films have been measured. The observed departure of these transport parameters from their respective bulk values can be understood in terms of intrinsic scattering due to enhanced crystallite boundaries. From the measured values of thermoelectric power and the corresponding temperature coefficient of resistance of annealed Cu, Ni, and Fe films, the calculated values of log derivative of the mean free path of conduction electrons at the Fermi surface with respect to energy (U) are found to be −0.51, 3.22, and −8.39, respectively. The thermoelectric response of annealed C...

Influence of Ball Milling Parameters on the Crystallite Size of Ba(Ti1-xZrx)O3

Ba(Ti1-xZrx)O3 ceramic powders were prepared by solid state reaction. The mono phase powders were then used to produce nano powder using high-energy ball milling. The crystallite sizes of each composition were investigated by varying the milling speed from 150 to 350 rpm fixing the milling time at 10 h and the milling time from 10 to 90 h, at a fixed speed of 250 rpm. X-ray diffraction analysis of the powder showed the single phase perovskite structure of Ba(Ti1-xZrx)O3 powders. The increase in milling speed and milling time showed reduction of crystallite size to a minimum value which increases with further increase in milling time. FTIR analysis of Ba(Ti1-xZrx)O3 ceramic powders before and after ball milling illustrated a change in force constant of M-O bond.

DEPOSITION OF WIDE BAND GAP DLC FILMS USING R.F. PECVD AT VERY LOW POWER

Wide band gap diamond-like carbon films (DLCs) are deposited on silicon (1 0 0) substrates using capacitive coupled radio frequency plasma-enhanced chemical vapor deposition (R.F. PECVD) technique. The deposition of films is carried out at a constant pressure (~5×10-2mbar) using acetylene precursor diluted with argon at constant R.F. power of 5 W. Raman spectroscopy of deposited DLC films shows broad G peak near 1550 cm-1 and a weak D peak near 1320 cm1. FTIR plot of DLC films shows a peak near 2900 cm-1 corresponding to C–H stretching mode and peaks below 2000 cm-1 corresponding to C–C modes and C–H bending modes. Maximum hardness of the deposited films is found to be ~15 GPa. Band gap of the DLC films is ~3.5 eV. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) pictures show that the deposited films are amorphous. Deposition mechanism of wide band gap DLC film is explained on the basis of subplantation model.

Correlation of Mechanical Properties with Surface Morphology of Diamond-Like Carbon Films Deposited By Plasma Enhanced Chemical Vapour Deposition Technique

Diamond like carbon (DLC) films are deposited on glass substrates by using radio frequency plasma enhanced chemical vapour deposition technique with the variation of RF power. DLC films are deposited by using argon and acetylene plasma, at pressure 5×10-2 mbar for 60 minutes. Various properties like surface morphology, hydrophobicity, nanohardness, and structural properties are studied by using atomic force microscope, contact angle measurement setup, nano-hardness tester and Raman spectrometer, respectively. Systematic variation in surface morphology with RF power has been observed. It has been observed that the morphology of the films is correlated with the hardness, sp3 content, roughness, and contact angle. Observed results have been explained using Raman spectra.

Diamond like rod-shaped carbon nanostructures grown by microwave plasma CVD

Diamond like nanosized structures were deposited where a modified microwave plasma CVD diamond growth recipe was used; here, instead of a clean molybdenum (Mo) holder, the Si(100) substrates were placed on iron oxide coated Mo holder. The growth of micron size diamond crystals were observed on clean areas whereas rod shaped carbon based nanostructures were observed on iron oxide rich areas. Furthermore, the growth of CNTs was also noticed on the plasma exposed parts of the Mo holder. Electron microscopy results suggest that some of the nanorods crystallize in the form of diamond.