Devendra Kumar
Articles written in Bulletin of Materials Science
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 9 Issue 4 November 1987 pp 255-262
Dielectric behaviour of glasses and glass ceramics in the system BaO-PbO-TiO2-B2O3-SiO2
R K Mandal Ch Durga Prasad O M Parkash Devendra Kumar
Glasses with varying molar ratios of PbO/BaO in the system BaO-PbO-TiO2-B2O3-SiO2 were prepared keeping (BaO + PbO)/TiO2 ratio equal to one. The glasses were ceramized by two-stage heat treatment. X-ray diffraction indicates that PbTiO3 crystallizes in lead-rich glasses while BaTiO3 precipitates in barium-rich compositions. Solid solution (Ba, Pb)TiO3 does not seem to crystallize over the entire range of compositions. Simultaneous presence of PbO and BaO in the initial glass composition reduces the yield of ferroelectric phase. Dielectric properties have been interpreted in terms of microstructural features.
Volume 10 Issue 3 May 1988 pp 245-250
Electrical conduction in the solid solution La1 −
O M Parkash Devendra Kumar Rabindra Kumar
Seebeck coefficient and DC resistivity of the solid solution La1 −
Volume 11 Issue 1 September 1988 pp 39-41
Preparation and characterization of Ca1 −
O M Parkash Ch Durga Prasad Devendra Kumar
The possibility of the formation of solid solution in the system Ca1 −
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 17 Issue 3 June 1994 pp 253-257
Electrical behaviour of lanthanum- and cobalt-doped strontium stannate
O M Parkash K D Mandal C C Christopher M S Sastry Devendra Kumar
Electrical properties of lanthanum- and cobalt-doped strontium stannate, SrSnO3, have been studied as a function of temperature. All the compositions investigated have cubic structure. Measurement of Seebeck coefficient in one of the cobalt-doped SrSnO3 sample shows that it exhibits
Volume 18 Issue 5 September 1995 pp 563-576
Equivalent circuit models for electronic ceramics
Lakshman Pandey O M Parkash Rajesh K Katare Devendra Kumar
Complex immittance spectra of model equivalent circuits involving resistive and capacitive elements are calculated. A comparison of experimentally obtained complex immittance plots with these diagrams greatly facilitates the search for the most appropriate equivalent circuit representing the electrical properties of electronic ceramics.
Volume 18 Issue 5 September 1995 pp 577-585
Dielectric and microstructural behaviour of strontium titanate borosilicate glass ceramic system
O P Thakur Devendra Kumar O M Parkash Lakshman Pandey
65(SrO·TiO2)−35(2SiO2·B2O3) wt% glass was synthesized. Differential thermal analysis study shows one exothermic peak which shifts towards higher temperature with increasing heating rate. Glass ceramics prepared by controlled crystallization of strontium titanate borosilicate glass produce uniform distribution of crystallites in a glassy matrix. Attempt was made to crystallize strontium titanate phase in this glass ceramic. Different phases precipitated out during ceramization have been identified by X-ray diffraction. It appears that due to high reactivity of SrO with B2O3, strontium borate crystallizes as principal phase followed by TiO2 (rutile) and Sr3Ti2O7 phases. Dielectric constant of these glass ceramics was observed to be more or less temperature independent over wide range of temperatures with low values of dielectric constant and dissipation factor.
Volume 19 Issue 2 April 1996 pp 393-404
O P Thakur Devendra Kumar O M Parkash Lakshman Pandey
Glass of the nominal composition 64 wt%(SrO·TiO2)·35 wt%(2SiO2·B2O3)-1 wt%(CoO) was prepared. The glass samples were subjected to heat treatment at 900 and 950 C. The phase progression in these glass ceramics from X-ray diffraction studies shows the formation of Sr2B2O5 as primary crystalline phase followed by rutile (TiO2), Sr3Ti2O7, SrB2Si2O8 and Sr3B2SiO8 as secondary phases. The first DTA exothermic peak of glass corresponds to the crystallization of Sr2B2O5, rutile and Sr3Ti2O7 phase while second crystallization peak may be assigned to the formation of SrB2Si2O8 and Sr3B2SiO8 phases. From microstructure studies we find that strontium borate grows with larger grain size whereas the other phases like Sr3Ti2O7, TiO2 appear smaller in size. Cobalt oxide content in the strontium titanate borosilicate glass ceramic gives the thermal stability to dielectric behaviour and decreases the dielectric loss.
Volume 19 Issue 3 June 1996 pp 513-525
Effect of composition on dielectric and electrical properties of the Sr1 −
Shail Upadhyay Devendra Kumar O M Parkash
Valence compensated perovskite system Sr1 −
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 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 3 June 2017 pp 527-535
Polymer-assisted co-precipitation route for the synthesis of Al$_2$O$_3$–13% TiO$_2$ nanocomposite
NEERA SINGH RANABRATA MAZUMDER PALLAV GUPTA DEVENDRA KUMAR
The present investigation reveals the effect of processing parameters on the properties of alumina–titania (Al$_2$O$_3$–TiO$_2$) nanocomposites. A polymer-assisted (Pluronic P123 triblock co-polymer) co-precipitation route has been employed to synthesize Al$_2$O$_3$–TiO$_2$ nanoparticles. As a surfactant, pluronic P123 polymer exhibits hydrophobic as well as the hydrophilic nature simultaneously which detains the agglomeration and hence the nano size particle have been obtained. Effect of surfactant concentration on morphology and particle size of product has also been investigated. Thermal behaviour of the prepared powder samples have been studied using differential scanning calorimeter/thermal gravimetric analysis and dilatometer. Formation of aluminium-titanate (Al$_2$TiO$_5$) phase has been confirmed using X-ray diffraction analysis. It has been observed by field emission scanning electron microscopy analysis that the particle size reduced effectively (below 100 nm) when polymer-assisted co-precipitation route is used instead of the simple co-precipitation technique. A highly dense microstructure of sintered samples has been obtained, driven by reduced particle size.
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
Continuous Article Publishing mode
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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