Om Parkash
Articles written in Bulletin of Materials Science
Volume 2 Issue 2 May 1980 pp 83-89 Articles
Characterisation of bubble materials
M J Patni Om Parkash D Bahadur
The rapid development of magnetic bubble technology has required growth to exacting specifications of a large number of magnetic films of garnets and some amorphous binary and ternary alloys of rare-earth and transition metals. The characterisation of these films is an essential part in the search for newer materials which hold out promise for better device performance and cost viability. Many methods of films characterisation have been reported from time to time. By and large, these methods can be divided into two groups: one, bulk measurements made on the film and two, measurements made on the domains. We have attempted to collate and briefly introduce various techniques to characterise magnetic bubble materials in this review.
Volume 3 Issue 3 November 1981 pp 325-331
Electron transport in hot pressed Y3−
D Bahadur OM Parkash Devendra Kumar
Electron transport properties of a few hot-pressed garnets of the series Y3−xGdxFe5O12 (where
Volume 8 Issue 1 February 1986 pp 13-21
Microstructural and dielectric behaviour of glass ceramics in the system PbO-BaO-TiO2-B2O3-SiO2
OM Parkash Devendra Kumar R Rajgopalan
Glasses in the system PbO-BaO-TiO2-B2O3-SiO2 with and without P2O5 as nucleant have been prepared. The glass samples were ceramized based on
Volume 8 Issue 5 December 1986 pp 557-565
Glass ceramics containing ferroelectric phases
Om Parkash Devendra Kumar Lakshman Pandey
Glass ceramics prepared by controlled crystallization of glasses produce fine dispersion of crystallites in a glassy matrix. Glasses containing a mjor portion of constituents of a ferroelectric phase produce crystallites of ferroelectric phase in glass through a suitable heat treatment. The amount of network former in the initial glass has a profound influence on its crystallization behaviour and microstructure of the resulting ferroelectric glass ceramics. The value of dielectric constant and the nature of ferroelectric to paraelectric transition depend on the crystallite size and volume fraction of the ferroelectric phase. These glass ceramics are transparent for crystallite size less than 0·1
Volume 9 Issue 2 June 1987 pp 123-130
Electrical properties of the system lanthanum lead cobalt titanium oxide
Devendra Kumar Ch Durga Prasad Om Parkash
Measurements of DC electrical resistivity and Seebeck coefficient on the perovskite system La1−
Volume 11 Issue 4 December 1988 pp 307-313
Dielectric properties of the system Ca1 −
Ch Durga Prasad H S Tewari Devendra Kumar Om Parkash
Dielectric behaviour of samples of the system Ca1 −
Volume 12 Issue 1 March 1989 pp 53-56
Studies on the spin-state equilibria of cobalt ions in the system La1−
Om Parkash N Chaturvedi M Tiwari Devendra Kumar
The spin-state equilibria of cobalt ions in the system La1−
Volume 20 Issue 1 February 1997 pp 67-77
O P Thakur Devendra Kumar Om Parkash Lakshman Pandey
Glasses in the system (65 −
Volume 20 Issue 7 October 1997 pp 933-947
Lakshman Pandey Rajesh K Katare Om Parkash Devendra Kumar
The electrical behaviour of valence-compensated ceramic system Ba1−
Volume 33 Issue 2 April 2010 pp 145-148 Ceramics and Glasses
IR study of Pb–Sr titanate borosilicate glasses
C R Gautam Devendra Kumar Om Parkash
The infrared spectra (IR) of various glass compositions in the glass system, [(Pb𝑥Sr1–𝑥)O.TiO2]– [2SiO2.B2O3]–[BaO.K2O]–[La2O3], were recorded over a continuous spectral range (400–4000 cm-1) to study their structure systematically. IR spectrum of each glass composition shows a number of absorption bands. These bands are strongly influenced by the increasing substitution of SrO for PbO. Various bands shift with composition. Absorption peaks occur due to the vibrational mode of the borate network in these glasses. The vibrational modes of the borate network are seen to be mainly due to the asymmetric stretching relaxation of the B–O bond of trigonal BO3 units. More splitting is observed in strontium-rich composition.
Volume 34 Issue 7 December 2011 pp 1393-1399
C R Gautam Devendra Kumar Om Parkash
Glasses were made by melt-quench method in the system [(Sr1–𝑥Pb𝑥)O.TiO2]–[2SiO2.B2O3]–5[K2O–BaO] (0.0 ≤ 𝑥 ≤ 0.4) with addition of 1 mol% Nb2O5. Perovskite strontium lead titanate in solid solution phase has been crystallized in borosilicate glassy matrix with suitable choice of composition and heat treatment schedule. Addition of 1 mol% of Nb2O5 enhances the crystallization of lead strontium titanate phase in the glassy matrix. Scanning electron microscopy (SEM) is performed to study the surface morphology of the crystallites and crystalline interface to the glass. Dielectric properties of these glass ceramics were studied by measuring capacitance and dissipation factor as a function of temperature at a few selected frequencies. Nb2O5 doped strontium lead titanate glass ceramic shows a high value of dielectric constant. It is of the order of 10,000 while the dielectric constant of undoped glass ceramic sample is of the order of 500. Complex impedance and modulus spectroscopic techniques were used to find out the contributions of polarization of crystallites and glass crystal interfaces to the resulting dielectric behaviour.
Volume 35 Issue 3 June 2012 pp 433-438
K D Mandal Alok Kumar Rai Laxman Singh Om Parkash
The effect of Co+2 doping on Cu+2 and Ti+4 sites in calcium copper titanate, CaCu3Ti4O12, has been examined. The doped compositions, CaCu3−𝑥Co𝑥Ti4O12 and CaCu3Ti4−𝑥Co𝑥O12 (𝑥 = 0.10) ceramics, were prepared by novel semi-wet route. In this method, calcium, copper and cobalt salts were taken in solution form and TiO2 was used in solid form. XRD analysis confirmed the formation of single-phase materials. Structure of CaCu3Ti4O12 does not change on doping with cobalt either on Cu-site or Ti-site and it remains cubic. Scanning electron micrographs (SEM) show average grain size of CaCu2.9Co0.1Ti4O12 to be larger than CaCu3Ti3.9Co0.1O12 ceramic. Energy dispersive X-ray spectroscopy (EDX) studies confined the purity of parent and Co-doped CaCu3Ti4O12 ceramics. Dielectric constant (𝜀r) and dielectric loss (tan 𝛿) of CaCu2.9Co0.1Ti4O12 is comparatively higher than that of CaCu3Ti3.9Co0.1O12 ceramic at all measured frequencies and temperatures.
Volume 36 Issue 5 October 2013 pp 859-868
Pallav Gupta Devendra Kumar Om Parkash A K Jha
The aim of this paper is to investigate the effect of sintering temperature and time on the properties of Fe–Al2O3 composite (5 wt% Al2O3; 95 wt% Fe) prepared by powder metallurgy process. X-ray diffraction, microstructure, density, hardness and compressive strength of prepared samples have been investigated. XRD studies show the presence of Fe and Al2O3 along with iron aluminate phase. Iron aluminate is formed as a result of reactive sintering between iron and alumina particles. Microstructural examination of the specimen showed a dense structure with nanosize dispersion of the reinforcement of ceramic phase. Density as well as hardness of specimens depend on the formation of iron aluminate phase, which in turn depends on sintering temperature and time.
Volume 39 Issue 5 September 2016 pp 1245-1258
PALLAV GUPTA DEVENDRA KUMAR A K JHA OM PARKASH
The present paper reports the effect of height to diameter ($h/d$) ratio on the deformation behaviour of Fe–Al$_2$O$_3$ metal matrix nanocomposites (MMNCs) during bulk processing. Sintered compacts were machined to the required size with different $h/d$ ratios. Test specimens were subjected to deformation at room temperature under three different interfacial friction conditions such as dry, solid and liquid lubrications. Deformed specimensshow a significant improvement in the density and hardness. Results also revealed the formation of a nanosize iron aluminate phase due to reactive sintering, which in turn contributes to grain refinement. Experimental density of the specimens was also verified with the theoretical density using the standard equations. It is expected that the present work will be useful in designing and developing MMNC products with better quality at competitive cost.
Volume 40 Issue 7 December 2017 pp 1497-1501
Electromagnetic interference shielding effectiveness of MgO−Al$_2$O$_3$−SiO$_2$ glass–ceramic system
PREETI KUMARI PANKAJ TRIPATHI OM PARKASH DEVENDRA KUMAR
MgO−Al$_2$O$_3$−SiO$_2$ (MAS)-based glass–ceramic system was prepared using very-low-cost raw materials, i.e.,talc, calcined alumina and calcined china clay with titanium dioxide as a nucleating agent. Glass–ceramics were preparedby a two-step process. In the first step, raw materials were mixed in the required proportion and melted at 1450$^{\circ}$C followedby water quench into a glassy frit. In the second step, powdered glass frit was uniaxially dry pressed into pellets followedby sintering at 1200$^{\circ}$C for 3h. X-ray diffraction pattern of the sintered compact shows well-defined peaks of cordieritealong with some anorthite and magnesium titanium oxide. The microstructure study of sample shows the presence of crystallineand glassy phases. Permittivity and permeability measurements were performed in the microwave frequency range12.4–17 GHz. The permittivity value of 5.7–6.0 and the permeability value of $\sim$1 were obtained. The reflection and transmission measurements show that the material possesses a shielding effectiveness in the range 2–10 dB over the frequencyrange 12.4–17 GHz.
Volume 46, 2023
All articles
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Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020
Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
Physical Sciences 2020
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