V. R. K. Murthy

Electrical conductivity and thermoelectric power measurements of some lithium-titanium ferrites

The electrical conductivity and thermoelectric power of some lithium–titanium ferrites with small amounts of manganese and zinc have been studied as a function of temperature in the range of 300–550 K and are reported here. The conductivity variation shows two different regions with a large variation in the activation energies. The possible mechanisms with respect to ionic conduction and electron hopping are discussed with the support of thermoelectric power measurements. Lattice parameters are also calculated from x‐ray diffractograms for confirming the single‐phase nature of the ferrites.

Structural Study on Ca0.6Sr0.4ZrO3

Structural study on the compound Ca0.6Sr0.4ZrO3 has been carried out. The study reveals that it is not isomorphous with its parent compounds CaZrO3 and SrZrO3. It belongs to the space group Pmcn and the size of the unit cell is 2ap×√ 2bp×2√ 2cp. The tilt system of the BO6 octahedra is found to be compound and the octahedra are highly distorted. The A-ions are displaced along the [001] direction by about 0.134 A and the displacements in adjacent layers are in the opposite directions.

A method for the evaluation of microwave dielectric and magnetic parameters using rectangular cavity perturbation technique

Abstract To derive the expression for complex dielectric and magnetic susceptibilities, an easy and alternate approach is proposed. This analysis is based on the assumption that the cavity is equivalent to an isolated lumped resonant circuit. The results are identical with standard expressions. Results of a few samples are also tabulated.

Microwave Dielectric Properties of Certain Simple Alkaline Earth Perovskite Compounds as a Function of Tolerance Factor.

Microwave dielectric properties of some simple alkaline earth perovskite compounds were studied with respect to the variation in the tolerance factor. It was found in the present study that the variation in dielectric constant (e), Qf o product and the temperature coefficient of polarizability with tolerance factor is quite opposite to what is observed in some complex perovskite materials. It was also observed that the temperature coefficient of dielectric constant follows the same trend as in some complex perovskite materials with respect to the tolerance factor.

Structural investigations on Pb(ZrxT1−x)O3 solid solutions using the X-ray Rietveld method

Solid solutions in the series Pb(ZrxTi1-x)O3 which belong to ABO3 type compounds were studied using the X-ray Rietveld technique from the tetragonal PbTiO3 end to Pb(Zr0.53 Ti0.47)O3 which is near the morphotropic phase boundary. A systematic structure analysis carried out for this series revealed that tetragonal and rhombohedral phases coexist even when Zr/Ti ratio is 40/60. Quantitative phase analysis using Rietveld method has been carried out for compositions falling in the two phase region. Substantial decrease in distortions of the BO6 octahedra has been observed for the compositions near the morphotropic phase boundary.

Vibrational, magnetic, and dielectric behavior of La-substituted BiFeO3-PbTiO3

Phonons and magnetic and ferroelectric ordering in La-substituted (Bi1−xLax)0.5Pb0.5Fe0.5Ti0.5O3 for samples with 0.0 ≤ x ≤ 0.5 are investigated using Raman, magnetization, and polarization measurements as a function of temperature. The system is tetragonal for pure Bi0.5Pb0.5Fe0.5Ti0.5O3 with a large c/a ratio. The anisotropy is reduced when Bi is partially replaced by La (0 ≤ x ≤ 0.5), and it turns cubic for x ≥ 0.4. All the properties are found to change significantly with changes in the c/a ratio. Evidence of spin-glass-like magnetic ordering at low temperature is found in the case of x = 0.2. A mechanism for the systematic change of magnetic ordering temperature as a function of doping is also discussed. The phonon frequencies and line widths exhibit discontinuous changes across the tetragonal-cubic transition. Large polarization and forbidden Raman scattering in the cubic phase are explained on the basis of symmetry breaking due to the formation of a polar nano region, which leads to relaxor behavior.

Far-infrared, Raman spectroscopy, and microwave dielectric properties of La(Mg0.5Ti(0.5−x)Snx)O3 ceramics

La(Mg0.5Ti(0.5−x)Snx)O3 perovskite ceramics with composition (x=0.0−0.5) are prepared by the solid state reaction method. The ceramics are characterized by x-ray diffraction, far-infrared reflectance, Raman spectroscopy, and microwave dielectric properties. The symmetry of ceramics is monoclinic with P21/n space group. Intrinsic dielectric constant and loss are estimated by fitting reflectance to the four-parameter semiquantum model. Transverse optic phonon mode strengths and average phonon damping are calculated. The modes corresponding to B-site ordering are identified in Raman spectra and the A1g mode of La(MgTi)0.5O3 is analyzed by assuming two merging modes. The variation of long-range order is correlated with full width half maximum of the A1g mode. Microwave measurements are carried out in the frequency range of 8–10 GHz. The dielectric constant (e′) is found to gradually decrease from 28.4 to 19.7 with an increase in tin concentration, whereas the temperature coefficient of resonant frequency (τf)...

Structural investigations on the (Ba,Sr)(Zr,Ti)O3 system

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.

Comparison of initial permeability of MgCuZn ferrites sintered by both conventional and microwave methods

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.

Optical reflection studies of the electronic properties of stages 2 – 5 graphite-SbCl5

Abstract We have measured the absolute reflectance spectra at near-normal incidence for well-characterized stages 2, 3, 4 and 5 graphite-SbCl 5 . The measurements were made with a prism monochromator in the range 0.1 – 3.0 eV. Because of the air stability of these compounds we have also been able to determine experimentally the values of the real and imaginary parts of the dielectric constant at 1.96 eV by measuring the absolute reflectance of the samples in air and CCl 4 using a HeNe laser. The reflectance spectra were analyzed in terms of a phenomenological dielectric constant model with contributions from the core, free carries, and interband transitions. Interband transitions are modeled as Lorentz oscillators. The spectra were fitted with the additional constraint that the calculated values of the real and imaginary dielectric constant at 1.96 eV matched those directly determined by experiment. The data are discussed in terms of the band model of Blinowski et al . and the more recent band model reported by Dresselhaus and Leung.