Showing papers by "V. R. K. Murthy published in 2011"

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

Abstract: 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.

Synthesis of lead free sodium bismuth titanate (nbt) ceramic by conventional and microwave sintering methods

Abstract: Dielectric studies were carried out on a lead free Sodium Bismuth Titanate, NBT, (Na0.5Bi0.5TiO3) composition. The material was synthesized by conventional ceramic method (CS) and microwave sintering (MS). The presence of single phase has been confirmed by X-ray diffraction and scanning electron microscopy of NBT ceramic. The later technique (MS) resulted in material with high density, dielectric properties and improved microstructure. The transition temperature was observed slightly higher for microwave sintered (MS) material. Longitudinal modulus measurements are very sensitive property to identify the phase transitions in ceramics. Longitudinal modulus (L) measurements were also employed on these samples in the frequency 136 kHz and can be studied in the wide temperature range 30°C to 400°C. The elastic behavior (L) showed a break at two temperatures (~200°C and 350°C) in both the conventional and microwave sintered ceramics. In NBT ceramics, permittivity anomalies are connected to modulus anomalies. The results are correlated with the dielectric measurements. This behavior explained in the light of structural phase transitions in the ferroelectric ceramics.

Microwave Hall mobility and electrical properties of electrospun polymer nanofibers

Abstract: Composite nanofibers from poly(methylmethacrylate)- (PMMA-) conducting polyaniline [PANI(HCl)] were prepared by using the electrospinning technique. The morphology and structural details of the fibers were characterized by SEM and the ac conductivity of the composite fibers found was measured to be ∼ 2.17×10−4 S/cm which is very good enhancement compared to that of pure PMMA and conductivity of PANI-PMMA thin films as well. The conductivity is found to increase with increase in the polyaniline content in the composite. Microwave Hall mobility measurements on electrospun nanofibers showed 17 cm2/V s for the lower loadings. With further increase in the polyaniline content in the composite, the mobility value decreases which is attributed to the increase in carrier-carrier scatterings.

Dielectric relaxation, thermodynamic and theoretical studies on hydrogen bonded polar binary mixtures of N-methyl aniline with propan-1-ol and isopropyl alcohol

Abstract: The dielectric relaxation studies on polar binary mixtures of N-methyl aniline with, alcohols, propan-1-ol and isopropyl alcohol have been carried out, at different temperatures and mole fractions, using — LF impedance analyzer, Plunger method and Abbe’s refractometer in radio, microwave and optic frequency regions respectively. Kirkwood effective correlation factor, corrective Kirkwood correlation factor, Bruggeman parameter, relaxation time and thermodynamical parameters are calculated using the experimental data. Conformational analysis of the formation of hydrogen bond in the equi molar binary mixture systems of N-methyl aniline with propan-1-ol and isopropyl alcohol is supported by experimental and theoretical FT-IR values.

Thermodynamic, Dielectric and Conformational Studies on Hydrogen Bonded Binary Mixtures of Propan-1-ol with Methyl Benzoate and Ethyl Benzoate

Abstract: Dielectric relaxation studies of propan-1-ol with alkyl benzoates (methyl benzoate and ethyl benzoate) have been carried out, for various mole fractions, at different temperatures using a LF impedance analyzer, Plunger method, and an Abbe’s refractometer in the radio, microwave and optical frequency regions, respectively. Kirkwood’s effective correlation factor, the corrective Kirkwood correlation factor, Bruggeman parameter, relaxation time, excess inverse relaxation time and thermodynamic parameters were calculated using the experimental data. Conformational analysis of the formation of hydrogen bonds in the equi-molar binary mixtures of propan-1-ol with alkyl benzoates is supported by experimental and theoretical FT-IR values.

Correlation studies on dielectric and thermodynamic parameters in the binary mixtures of N-methyl aniline and alcohols

Abstract: The dielectric and thermodynamic studies on polar binary mixtures of N- methyl aniline with alcohols — propan-1-ol and propan-2-ol have been carried out, at different temperatures and mole fractions. LF impedance analyzer, Microwave bench and Abbe’s refractometer are used respectively in radio, microwave (X-Band) and high frequency regions to determine the dielectric data. The experimental data is used to correlate the dielectric and thermodynamic parameters — static permittivity, high frequency permittivity, Kirkwood effective correlation factor, corrective Kirkwood correlation factor, excess permittivity, excess Helmholtz free energy, dipole moment, excessive dipole moment, relaxation time, excess inverse relaxation time and the excess thermodynamic parameters. These parameters are used to interpret the molecular interactions between the molecular species of the liquid mixtures.

Investigations on Binary Mixtures of Propan-2-ol with Methyl Benzoate and Ethyl Benzoate

Abstract: The molecular interactions between the polar systems propan-2-ol with alkyl benzoates (methyl benzoate and ethyl benzoate), for various mole fractions and different temperatures, were studied by determining the dielectric permittivity using a LF impedance analyzer and Abbe’s refractometer in the static and optical frequency regions, respectively. The effective Kirkwood correlation factor, corrective Kirkwood correlation factor, dipole moment, excess dipole moment, and excess Helmholtz free energy were calculated using the experimental data. Hamiltonian quantum mechanical calculations (ab initio and semiempirical) were performed using PC Spartan and Argus lab Modeling software for both pure and equimolar binary systems of propan-2-ol with alkyl benzoates.

STRUCTURAL, ELECTRICAL AND MAGNETIC CHARACTERIZATION OF Ni–Cu–Zn SPINEL FERRITES

Abstract: Ni–Cu–Zn ferrite materials have been extensively used in multilayer chip inductors because of their remarkable properties at higher frequencies. In the present work, single phase Ni0.35Cu0.05Zn0.60Fe1.98O4-δ ferrite, has been prepared by microwave sintered (MS) method. In comparison with the conventional sintering method (CS), the sintering temperature and time for this MS method were significantly reduced to 30 min and 950°C from 5 h and 1250°C for the CS process. The frequency dependence of the dielectric properties such as dielectric constant (e'), dielectric loss (tan δ) were studied. The temperature dependence of magnetic initial permeability (μi) was studied. The saturation magnetization was also studied as a function of magnetic field. These microwave sintered ferrites results were compared with the properties of ferrites prepared by conventional sintering method in normal heating. Microwave sintering improves structural as well as electromagnetic parameters measured and thus makes the ferrite more suitable in microwave applications and electromagnetic devices.

MAGNETO-ELECTRIC EFFECT IN MULTIFERROIC Ni0.93Co0.02Mn0.05Fe1.95O4-δ/PbZr0.52Ti0.48O3 PARTICULATE COMPOSITES: DIELECTRIC, PIEZOELECTRIC PROPERTIES

Abstract: Magnetoelectric composites have been synthesized by sintering mixtures of highly piezoelectric component Pb(Zr0.52Ti0.48)O3, PZT and highly magnetostrictive piezomagnetic component Ni0.93Co0.02Mn0.05Fe1.95O4-δ, NCMF. These composites with generic formula (1 - x)PZT + xNi0.93Co0.02Mn0.05Fe1.95O4-δ, where x varies as 0.1, 0.3 and 0.5 mole fractions, were prepared from the powders of the pure components by the conventional ceramic route. The presence of two phases in multiferroic was confirmed by XRD technique. The variation of dielectric constant and dissipation factor, as a function of frequency from 100 Hz to 1 MHz and in the temperature range of 30–500°C were studied. The piezoelectric d33 coefficient of these composites was also studied in these composites. The magnetoelectric (ME) output voltage was measured in terms of the dE/dH as a function of magnetic bias field. A high value of ME output (1200 mV/Oe · cm) was obtained in the composite containing 70% ferroelectric phase (PbZr0.52Ti0.48O3) and 30% ferrite phase (Ni0.93Co0.02Mn0.05Fe1.95O4-δ). These multiferroic particulate composites are used as sensors and transducers.

Correlation Between Tolerance Factor and Temperature Coefficient of Dielectric Constant of (Ba,Sr)(Zn1/3Ta2/3)O3 Dielectric Resonator

Abstract: The effect of substitution of Sr at the A site of Ba(Zn1/3Ta2/3)O3 was investigated with respect to tolerance factor (t) which determines the degree of packing of A and B site ions of perovskite unit cell, with an intension to understand the correlation between the temperature dependent dielectric properties with structure. The investigation reveals that the Ba rich compositions with highly symmetric cubic phase exhibits negative variation of dielectric constant with temperature and the Sr rich compositions with distorted structure always show positive variation of dielectric constant with temperature. The profile of τe variation of all the compositions was scaled with respect of reduced temperature which exhibits an exact signature of τe variation with the compositions at room temperature. The observed mechanism was explained using Clausius Mossoti equation.