S. K. Rout

Optical and dielectric relaxor behaviour of Ba(Zr0.25Ti0.75)O3 ceramic explained by means of distorted clusters

In this work, Ba(Zr0.25Ti0.75)O3 ceramic was prepared by solid-state reaction. This material was characterized by x-ray diffraction and Fourier transform Raman spectroscopy. The temperature dependent dielectric properties were investigated in the frequency range from 1 kHz to 1 MHz. The dielectric measurements indicated a diffuse phase transition. The broadening of the dielectric permittivity in the frequency range as well as its shifting at higher temperatures indicated a relaxor-like behaviour for this material. The diffusivity and the relaxation strength were estimated using the modified Curie–Weiss law. The optical properties were analysed by ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) measurements at room temperature. The UV–vis spectrum indicated that the Ba(Zr0.25Ti0.75)O3 ceramic has an optical band gap of 2.98 eV. A blue PL emission was observed for this compound when excited with 350 nm wavelength. The polarity as well as the PL property of this material was attributed to the presence of polar [TiO6] distorted clusters into a globally cubic matrix. (Some figures in this article are in colour only in the electronic version)

Phase transition in ABi4Ti4O15 (A=Ca,Sr,Ba) Aurivillius oxides prepared through a soft chemical route

A series of compounds, CaBi4Ti4O15 (CBT), SrBi4Ti4O15 (SBT), and BaBi4Ti4O15 (BBT), belonging to the Aurivillus-type structure (four layers) has been prepared by a modified chemical route. Different oxalates were precipitated from their respective nitrate solution onto the surface of TiO2 powders. The room temperature x-ray diffraction study reveled that the compounds were having orthorhombic symmetry. Considering the tolerance factor, a significant deformation of the perovskite block is observed and that decreases with increase in ionic radius of A site atom. Temperature dependent dielectric study showed normal ferroelectric to paraelectric transition well above the room temperature except for BBT. The BBT ceramic showed a relaxorlike behavior near phase transition. The quantitative characterization and comparison of relaxor behavior were based on empirical parameters γ and ΔTres. The dielectric relaxation rate follows the Vogel–Fulcher relation with activation energy=0.02 eV and freezing temperature=362...

Effect of Neodymium on Optical Bandgap and Microwave Dielectric Properties of Barium Zirconate Ceramic

The ceramics with general formula Ba(1−x) Nd(2x/3)ZrO3 (x = 0.0,0.02, 0.04, 0.06, 0.08, and 0.1) were prepared by solid-state reaction. The phase formation of the powders was analyzed by means of X-ray diffraction (XRD), Fourier transform-Raman (FT-Raman), and Fourier transform infrared (FTIR) spectroscopy. XRD patterns revealed that all powders show a perovskite-type cubic structure with space group Pm-3m. FT-Raman and FTIR spectra suggested the formation of higher degree of symmetry in the crystal. The optical bandgap was found to be decreasing while Urbach energy was found to be increasing with an increase of Nd3+ content. The surface morphology of sintered pellets was studied by scanning electron microscope. Microwave dielectric constant and quality factor were investigated by the TE01δ mode dielectric resonator method. The microwave dielectric constant and temperature coefficient of resonant frequency decreases with increase in of Nd3+ content. The irregular nature of quality factor (Q × f) was observed due to the extrinsic losses in materials. The dielectric resonator antenna (DRA) characteristics were investigated experimentally and numerically using a monopole antenna through an infinite ground plane and Ansoft’s high-frequency structure simulator software, respectively. The resonant frequency and bandwidth of DRAs were also investigated for the ceramics.

Structural, electrical, and optical properties of (Ba1−xNd2x/3)TiO3 ceramics

In this paper, we report the obtention of barium neodymium titanate (Ba1−xNd2x/3)TiO3 ceramics with (0.00 ≤ x ≤ 0.10) by the solid-state reaction method. Structural studies suggested a phase transition from tetragonal to cubic structure with increase in Nd3+ ion content, supported by Rietveld refinement method. Photoluminescence properties revealed that the introduction of Nd3+ ions created structural disorder by means of A-site vacancies and displacement of M–O bond leading to shallow defects. Optical band gap value calculated from ultraviolet–visible spectra decreased with increase in Nd3+ ion concentration. A drastic decrease in grain size of undoped barium titanate was observed with introduction of Nd3+ ions through scanning electron microscopic images. Dielectric properties showed a gradual decrease in the Curie temperature with increase in Nd3+ ion content along with pinching effect. Normal ferroelectric character was obtained within the doping limit. P–E hysteresis loop showed a decrease in remnant polarization and coercive field. However, the composition x = 0.08 and 0.10 showed paraelectric behavior.

Microwave Dielectric Properties of Ni 0.2 Cu X Zn 0.8-X FE 2 O 4 for Application in Antenna

Structural, vibrational and microwave dielectric properties of Nickel-Copper-Zinc ferrite (Ni0.2CuxZn0.8−xFe2O4) ceramics have been presented in this paper. Samples have been prepared using conventional auto-combustion method. The X-ray diffraction (XRD) results confirmed the ferrite samples to be of cubic spinel structure, which further was validated by Fourier transform infrared (FT-IR) and Raman spectroscopy. The relative permittivity (εr) increased from 7.474 to 8.132 with successive increase in Cu content. The observed and calculated permittivity using ClausiusMossoitti relation have been in good agreement. The temperature coefficient of resonant frequency (τf ) decreased from −75.85 ppm/◦C to −32.12 ppm/◦C with increase in successive Cu content. The relative permeability (μr) have been calculated by using the Nicholson-Ross-Weir conversion technique. Using Ni0.2Cu0.2Zn0.6Fe2O4 sample the ferrite resonator antennas have been designed in three different shapes. The experimental and theoretical characteristics of the antennas have been compared and a good agreement has been achieved.

Diffuse phase transition of BaTi0.6Zr0.4O3 relaxor ferroelectric ceramics

BaTi0.6Zr0.4O3 ceramic was prepared through solid state reaction route. X-ray diffraction showed that the composition has cubic perovskite structure with space group Pm-3m at room temperature. Temperature dependency dielectric study of the ceramic has been investigated. Bulk density was determined using Archimedes principle and found to be ∼97% of X-ray density. The average grain size in the pallet is measured by an optical microscope and found to be 22.23 µm. The dielectric measurement revealed diffuse phase transition of second-order, where dielectric peak temperature (T m) is dependent of frequency showing relaxor-type behaviour. A clear deviation from Curie–Weiss law is observed in the paraelectric region. The dielectric relaxation rate follows the Vogel–Fulcher relation with E a = 0.1020 eV, T f = 106 K, ν0 = 8.5 × 1011 Hz.

Electronic transport in LCMO/BTO composites

A series of (1 − x)La0.67Ca0.33MnO3/(x)BaTiO3 composites has been synthesized by the solid state route. Microstructural and transport studies on these samples show a complete immiscibility between metallic ferromagnet, La0.67Ca0.33MnO3 (LCMO) and insulating ferroelectric, BaTiO3 (BTO). Temperature dependent electrical transport studies show evidence of both intrinsic and extrinsic colossal magnetoresistance (CMR) effects. Inclusion of BTO in LCMO phase results in high resistive samples with a metal-insulator transition at temperature Tp 1 originating from intrinsic effect and another dominant metal-insulator transition at temperature Tp 2 caused because of extrinsic effect. Tp 2 decreases up to a certain percentage of BTO content above which this trend of variation is reversed.

Anodic vacuum arc developed nanocrystalline Cu-Ni and Fe-Ni thin film thermocouples

This paper deals with the development of nanocrystalline Cu–Ni and Fe–Ni thin film thermocouples (TFTCs) by using ion-assisted anodic vacuum arc deposition technique. The crystallographic structure and surface morphology of individual layer films have been studied by x-ray diffraction and scanning electron microscopy, respectively. The resistivity, temperature coefficient of resistance, and thermoelectric power of as deposited and annealed films have been measured. The observed departure of these transport parameters from their respective bulk values can be understood in terms of intrinsic scattering due to enhanced crystallite boundaries. From the measured values of thermoelectric power and the corresponding temperature coefficient of resistance of annealed Cu, Ni, and Fe films, the calculated values of log derivative of the mean free path of conduction electrons at the Fermi surface with respect to energy (U) are found to be −0.51, 3.22, and −8.39, respectively. The thermoelectric response of annealed C...

Structural and scaling behavior in relaxor ferroelectric BZT ceramic doped with rare earth europium ion

Rare earth Eu3+ ion doped barium zirconate titanate (Ba1-xEu2x/3Zr0.3Ti0.7)O3 (x = 0.00 - 0.10) ceramics were prepared by using the solid state reaction route and the effect of doping concentration on structural and dielectric relaxation behavior of the ceramics were studied. The structural and microstructural analyses of the materials were done by using X-ray diffraction, Raman and SEM techniques respectively. Sharp and well defined diffraction peaks revealed that all the materials are of single phase cubic perovskite structure with space group Pm-3m. Microstructural study on the sintered pellets revealed that the grain size decreases initially with Eu concentrations followed by increasing trends in higher concentrations. Raman spectroscopic study revealed that the substitution of Ba2+ ion by Eu3+ ions shifted the Raman active modes towards higher energy side, which indicated that these materials undergo an increase in average cubicity with increase in Eu3+ ions concentrations. The signature of relaxor behavior and diffuse types of phase transition were detected by monitoring the relative intensity of Raman features. The broadening in the dielectric permittivity and the frequency dependence behavior with increase in frequency indicated a relaxor behavior in these materials. Lorentzian type law was used to describe the dielectric relaxation behavior over wide range of temperature.

Phase transition and energy storage properties of BaTiO3-modified Bi0.5(Na0.8K0.2)0.5TiO3 ceramics

ABSTRACT Perovskite type (1-x)Bi0.5(Na0.8K0.2)0.5TiO3–xBaTiO3 (x = 0.0–0.05) ceramics were prepared by conventional solid state reaction method. X-ray diffraction revealed a phase transition from rhombohedral and tetragonal mixed phase to tetragonal phase at x = 0.05. The signature of lattice disorder generated due of differences in ionic radius of cations at A-site is analyses using Raman spectra. The broadening of dielectric peak and its frequency dependence behaviour near Td is considered as relaxor behaviour of these ceramics. Addition of BT, reduces remnant polarization and hysteresis loss is suggested the possibility of energy storage ability of these ceramics.