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V. R. K. Murthy

Bio: V. R. K. Murthy is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Dielectric & Rietveld refinement. The author has an hindex of 27, co-authored 162 publications receiving 2595 citations. Previous affiliations of V. R. K. Murthy include VIT University & Indian Institute of Science.


Papers
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Journal ArticleDOI
TL;DR: Li 2 Zn (1− x ) Ni x Ti 3 O 8 ( x ǫ= 0, 0.1, 0.4 and 1.0) microwave dielectric ceramics were studied with the help of powder X-ray diffraction and Raman spectroscopic measurements as discussed by the authors.

33 citations

Journal ArticleDOI
TL;DR: In this article, structural and spectroscopic studies were carried out to understand the variation of dielectric properties with x. The symmetry of the compositions was determined to be monoclinic with space group P21/n, which corresponds to the a−a−c+ tilting system.
Abstract: The complex perovskite system (1−x)La(MgSn)0.5O3–xNd(MgSn)0.5O3 with the composition (x=0–1) was prepared by the solid state reaction method. Structural and spectroscopic studies were carried out to understand the variation of dielectric properties with x. Rietveld refinement was carried out with the initial model obtained by using the structure prediction and diagnostic software. The symmetry of the compositions was determined to be monoclinic with space group P21/n, which corresponds to the a−a−c+ tilting system, and the long-range order parameter was found to decrease with an increase in neodymium concentration. Raman spectra were analyzed by fitting the A1g-like mode to a Lorentzian peak shape. Intrinsic dielectric parameters were estimated by fitting infrared reflectance spectra with the four-parameter semiquantum model. Transverse optic phonon mode strengths and average phonon damping were calculated. The origin of increase in the intrinsic loss with the composition variation is discussed. Microwave...

32 citations

Journal ArticleDOI
TL;DR: In this paper, structural analysis of Ba0.73ZryTi1-yO3 has been carried out and the tilt angle with respect to the pseudocubic [100] and [001] directions increases with the Zr content.
Abstract: Structural investigations of the compounds in the series Ba0.27Sr0.73ZryTi1-yO3 have been carried out. The crystal structure goes to lower symmetry with increasing Zr content and the tolerance factor decreases. The variation of Va/Vb is linear with the tolerance factor. The tilt system is a-a-c0 for compositions with y = 0.50 and 0.65. The tilt system is a-a-c+ for compositions with y = 0.80, 0.90 and 0.97 and for BSZT (Ba0.29Sr0.71Zr0.97Ti0.03O3) and BSZTTa (Ba0.29Sr0.71Zr0.95Ti0.04Ta0.01O3). The tilt angle with respect to the pseudocubic [100] and [001] directions increases with the Zr content. For compositions with y = 0, 0.25 and 0.40, the coordination of the A ion (Ba or Sr) is 12, whereas the A-ion coordination number is 11 for compounds with y = 0.50 and 0.65 and it is lower for compositions with y = 0.80, 0.90 and 0.97 and for the compounds BSZT and BSZTTa. The decrease in coordination number indicates that the compounds are becoming more and more covalent with increasing Zr content. A graph of |90°-pc| against the tolerance factor shows that |90°-pc| falls sharply at a tolerance factor corresponding to the compositions used in the fabrication of dielectric resonators. TCf values show that the sign of this parameter changes at a tolerance factor near 0.965 and has a minimum for compounds with orthorhombic Pbnm/Pnma structures.

29 citations

Journal ArticleDOI
TL;DR: In this paper, a series of non-stoichiometric MgCuZn ferrites (Mg0.5−xCuxZn0.9O4−δ) have been successfully synthesized by both conventional and microwave sintering techniques.
Abstract: NiCuZn ferrites are widely employed for many electronic applications, but can be replaced by MgCuZn ferrites owing to their superior properties like low magnetostriction, environmental stability, low stress sensitivity and low cost. In view of this, a series of non-stoichiometric MgCuZn ferrites (Mg0.5−xCuxZn0.5Fe1.9O4−δ with x = 0.0, 0.05, 0.10, 0.15, 0.20, 0.25) have been successfully synthesized by both conventional and microwave sintering techniques. The non-stoichiometry was intentionally introduced into the ferrites to ensure high resistivity of the samples. X-ray diffraction patterns confirm the single phase spinel structure in both cases. The elemental composition of these ferrites was analysed by energy-dispersive x-ray spectrometry. The samples sintered by the microwave technique were found to be denser than the conventionally sintered samples. The initial permeability of MgCuZn ferrites was studied with an increase in copper concentration from x = 0.0 to 0.25. The temperature variation of the initial permeability of these samples was carried out from 30 °C to 150 °C. The results are discussed in the light of microstructure variations of the conventionally and microwave sintered samples. The phenomena involved in microwave sintering are also discussed.

28 citations

Journal ArticleDOI
TL;DR: Temperature- and composition-induced phase transition in SmNbO4 was studied by differential scanning calorimetry, Raman spectroscopy and high-temperature powder X-ray diffraction measurements and revealed a monoclinic fergusonite crystal structure at ambient temperature and transforms to a tetragonal scheelite structure above the transition temperature.
Abstract: Temperature- and composition-induced phase transition in SmNbO4 was studied by differential scanning calorimetry, Raman spectroscopy and high-temperature powder X-ray diffraction measurements. In situ X-ray diffraction studies revealed that SmNbO4 possesses a monoclinic fergusonite crystal structure at ambient temperature and transforms to a tetragonal scheelite structure above the transition temperature (To ≥ 800 °C). The second-order nature of this transition was confirmed by observing a linear relationship between the spontaneous strain (es) of SmNbO4 and the Landau order parameter (η) around the phase transition temperature. We stabilized this high-temperature tetragonal scheelite phase at ambient temperature by substituting Si4+ and Mo6+ into the Nb site of SmNbO4. The SmNb1−x(Si1/2Mo1/2)xO4 (x = 0.0–0.69) ceramic compositions were prepared by the conventional solid-state reaction method. Rietveld refinement was carried out on all the compositions to examine the phase purity, and the compositions where x < 0.06 all formed a monoclinic fergusonite structure (I2/a space group, Z = 2). Both the X-ray diffraction and Raman spectroscopy measurements revealed that increasing the concentration of x transformed the structure from monoclinic fergusonite to tetragonal scheelite (I41/a space group, Z = 4) at a critical concentration (xc). Both the monoclinic and tetragonal phases coexisted in the composition range of 0.06 ≤ x < xc. The Hakki–Coleman and reflection cavity techniques were used to measure the dielectric constant and quality factor of these stabilized phases, respectively. The temperature coefficient of the resonant frequency was measured by using an invar cavity attached to a programmable hot plate. The high-density samples possessed good microwave dielectric properties.

26 citations


Cited by
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[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Proceedings Article
01 Jan 1999
TL;DR: In this paper, the authors describe photonic crystals as the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures, and the interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.
Abstract: The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

2,722 citations

01 Sep 1955
TL;DR: In this paper, the authors restrict their attention to the ferrites and a few other closely related materials, which are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present.
Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

2,659 citations

Journal ArticleDOI
TL;DR: In this article, a 3d transition metal-doped ZnO films (n-type Zn1−xMxO) were formed on sapphire substrates using a pulsed-laser deposition technique, and their magnetic and electric properties were examined.
Abstract: 3d-transition-metal-doped ZnO films (n-type Zn1−xMxO (x=005–025): M=Co, Mn, Cr, Ni) are formed on sapphire substrates using a pulsed-laser deposition technique, and their magnetic and electric properties are examined The Co-doped ZnO films showed the maximum solubility limit Some of the Co-doped ZnO films exhibit ferromagnetic behaviors with the Curie temperature higher than room temperature The magnetic properties of Co-doped ZnO films depend on the concentration of Co ions and carriers

1,852 citations

Journal ArticleDOI
TL;DR: In this paper, a review focusing on promising candidate materials (such as GaN, GaP and ZnO) is presented, where the introduction of Mn into these and other materials under the right conditions is found to produce ferromagnetism near or above room temperature.
Abstract: Recent advances in the theory and experimental realization of ferromagnetic semiconductors give hope that a new generation of microelectronic devices based on the spin degree of freedom of the electron can be developed. This review focuses primarily on promising candidate materials (such as GaN, GaP and ZnO) in which there is already a technology base and a fairly good understanding of the basic electrical and optical properties. The introduction of Mn into these and other materials under the right conditions is found to produce ferromagnetism near or above room temperature. There are a number of other potential dopant ions that could be employed (such as Fe, Ni, Co, Cr) as suggested by theory [see, for example, Sato and Katayama-Yoshida, Jpn. J. Appl. Phys., Part 2 39, L555 (2000)]. Growth of these ferromagnetic materials by thin film techniques, such as molecular beam epitaxy or pulsed laser deposition, provides excellent control of the dopant concentration and the ability to grow single-phase layers. T...

968 citations