R. K. Dwivedi

Dielectric relaxation in valence compensated solid solution Sr0.65La0.35Ti0.65Co0.35O3

The valence compensated solid solution Sr0.65 La0.35 Ti0.65 Co0.35 O3 has been found to exhibit dielectric relaxor behaviour with a very high value of the dielectric constant. In the present investigation, this composition has been prepared using different processing parameters and routes, viz (a) solid-state sintering at 1350 °C followed by furnace cooling, (b) sintering at 1350 °C followed by annealing at 1000 °C, (c) sintering the sample prepared by the sol-gel route at 1100 °C and (d) sintering the powder prepared by the solid-state ceramic route at 1350 °C with 1 wt% SiO2 as a sintering aid. The dielectric characteristics were measured in the temperature range 300-500 K and frequency range 0.1 kHz-1 MHz. The dielectric characteristics of this composition are greatly influenced by processing parameters and routes. The dielectric relaxation in these materials was studied using impedance and modulus spectroscopic techniques.

Valence compensated perovskite oxide system Ca1−xLaxTi1−xCrxO3 Part III Impedance spectroscopy

Electrical behaviour of the compositions with x≤ 0.50 in the Ca1−xLaxTi1−xCrxO3system has been studied by employing complex plane impedance and spectroscopic analysis in the temperature range 100 K–550 K. These studies have revealed the contribution of three processes to the total electrical conductivity of these samples. An equivalent electrical circuit model, which contains series arrangement of three paralle RC elements, is proposed to represent the electrical characteristics of these materials. Out of these three, two processes correspond to the activated hopping processes within the bulk while the third process corresponds to the barrier layer formation in these ceramics. Immittance spectroscopic analysis shows that conduction occurs through localized as well as long range movement of charge carriers.

Valence compensated perovskite oxide system Ca1−xLaxTi1−xCrxO3 Part I Structure and dielectric behaviour

Attempts have been made to synthesize compositions with x = 0.01, 0.03, 0.05, 0.10, 0.20, 0.30 and 0.50 in the valence compensated system Ca1−xLaxTi1−xCrxO3by solid state ceramic method. Solid solutions form upto x≤ 0.50. All the compositions have been found to have orthorhombic structure. The structure of the compositions upto x≤ 0.10 is similar to that of CaTiO3. The structure changes gradually from CaTiO3to LaCrO3in the composition range 0.10 < x < 0.50. Dielectric constant, at room temperature, has been found to increase with increasing substituent concentration upto x= 0.30 and thereafter it decreases with increasing xupto 0.50. Orientational and space charge polarizations contribute to the dielectric behaviour of these materials.

Phase transformation, improved ferroelectric and magnetic properties of (1 − x) BiFeO3–xPb(Zr0.52Ti0.48)O3 solid solutions

The authors prepared (1 − x)BiFeO3 – (x)Pb(Zr0.52Ti0.48)O3 for x ≤ 0.30 by sol-gel method and investigated the materials structures, magnetic and electrical properties. Detailed Rietveld analysis of X-ray diffraction data revealed that the system retains distorted rhombohedral R3c structure for x ≤ 0.10 but transforms to monoclinic (Cc) structure for x > 0.10. Disappearance of some Raman modes corresponding to A1 modes and the decrease in the intensities of the remaining A1 modes with increasing x in the Raman spectra, which is a clear indication of structural modification and symmetry changes brought about by PZT doping. Enhanced magnetization with PZT doping content may be attributed to the gradual change and destruction in the spin cycloid structure of BiFeO3. The leakage current density at 3.5 kV/cm was reduced by approximately three orders of magnitude by doping PZT (x = 0.30), compared with BFO ceramics.

Investigation of MPB region in lead free BLNT-BCT system through XRD and Raman spectroscopy

Lead free piezoelectrics [1-x{(Bi0.96La0.04)0.5Na0.5TiO3}−x(Ba0.90Ca0.10TiO3)] (BLNT-BCT) with compositions x ≤ 0.20 have been synthesized by a semi-wet route and the compositions around the MPB region have been systematically investigated using x-ray diffraction and Raman spectroscopy. X-ray diffraction analysis confirms phase formation without any traces of secondary phases. Rietveld refinement of x-ray diffraction data revealed different structural symmetry for a different range of compositions viz., (i) rhombohedral (R3c) [x ≤ 0.08] (ii) rhombohedral (R3c) + tetragonal (P4mm) (MPB) [0.10 ≤ x ≤ 0.15] (iii) tetragonal (P4mm) [0.15 < x ≤ 0.20], which is confirmed by Raman spectroscopy. The structural phase transitions have been correlated with piezoelectric properties and the composition with x = 0.12 depicts better piezoelectric properties amongst studied compositions, which is attributed to the coexistence of rhombohedral and tetragonal phases.

Valence compensated perovskite oxide system Ca1−xLaxTi1−xCrxO3 Part II Electrical transport behavior

Electrical transport behaviour of the valence compensated system Ca1−xLaxTi1−xCrxO3(x≤ 0.50) has been investigated by studying the Seebeck co-efficient, DC and AC conductivity as a function of temperature. Seebeck co-efficient, DC conductivity of different compositions has been measured in the temperature range 300 K–1000 K. AC conductivity for different compositions were determined in the temperature range 100–550 K and frequency range 10 Hz–10 MHz. Positive values of Seebeck co-efficient show that holes are the majority charge carriers. Conduction seems to occur by correlated barrier hopping of holes among Cr3+and Cr4+ions or VO•and VO••. Almost equal values of activation energies obtained for DC conductivity and dielectric relaxation process show that both the processes occur by the same mechanism.

Effect of Rare Earth Gadolinium Substitution on the Structural, Microstructure and Dielectric Properties of Lead free BNT Ceramics

Piezoelectric materials have wide applications in today’s advanced technologies. However, most commercially used piezoelectric material PZT (PbZr1-xTixO3) is now strictly restricted worldwide due to hazardous nature of Pb. Research for the development of new lead free materials with properties comparable to that of PZT is in progress in recent years. In the present work, an effort has been made to synthesize low amount of rare earth gadolinium modified (Bi1-xGdx)0.5Na0.5TiO3 (BGNT) with compositions (x) = 0, 0.02, 0.03 and 0.04 by a novel Semi–Wet Technique. The structural, microstructure, phase transition and dielectric properties have been investigated. The XRD patterns have shown single phase formation for all the samples with a rhombohedral symmetry at RT. Gd3+ doping has shown a significant effect on the grain growth. The dielectric measurement has been carried out over the temperature range from RT to 400 oC at 1, 10 and 100 kHz frequency. It has been observed from the εr vs T plots that two phase transitions (i) ferroelectric to anti-ferroelectric and (ii) anti ferroelectric to paraelectric occur in all the samples. The composition with x = 0.02 has shown significantly high value of dielectric constant (εr ~ 1567) and low value of dielectric loss (Tan δ ~ 0.043) at room temperature.

Diffuse phase ferroelectric vs. Polomska transition in (1-x) BiFeO3-(x) Ba Zr0.025Ti0.975O3 (0.1 ≤ x ≤ 0.3) solid solutions

Investigations on the solid solutions (1-x) BiFeO3 - (x) Ba Zr0.025Ti0.975O3 (0.1 ≤ x ≤ 0.3) in the temperature range 300–750 K show colossal permittivity behavior and the occurrence of diffuse phase ferroelectric transition along with frequency dependent anomaly which disappears at temperature ∼450 K. For x = 0.3, these anomalies have been verified through differential scanning calorimetry and dielectric/impedance/conductivity measurements. The occurrence of peak in pyrocurrent (dPs/dT) vs. T plots also supports phase transition. With the increasing x, transition temperature decreases and diffusivity increases. This anomaly is absent at high frequencies (>100 kHz) in conductivity plots, indicating Polomska like surface phase transition, which is supported by modulus study.

Synthesis, Crystallization, and Dielectric Behaviour of Lead Bismuth Titanate Borosilicate Glasses with Addition of 1% La2O3

Lead bismuth titanate borosilicate glasses were prepared in the glass system 65[()·TiO3]-34[2SiO2·B2O3]-1La2O3 () doped with one mole percent of via conventional melt quench method. The amorphous nature of glass samples in this glass system is confirmed by using X-ray diffraction (XRD) study. Differential thermal analysis (DTA) has been employed to determine the glass transition temperature, , as well as crystallization temperature, . DTA measurements were recorded in temperature range from 30 to 1200°C. The prepared glasses were crystallized by regulated controlled heat treatment process on the basis of their DTA results. These samples are carried out for XRD measurements in the 2 range from 20 to 80° to study the crystallization behaviour and phase formation of the glass ceramic samples. The scanning electron microscopy (SEM) of these glass ceramic samples has been carried out to explore the morphology through nucleation and growth of the crystallites in the glassy matrix. The values of dielectric constant as well as dielectric loss were increased with increasing the temperature within the frequency range from 20 Hz to 100 Hz. The addition of 1 mol% of to the lead bismuth titanate glasses enhances the crystallization and acts as donor dopant for this glass system.

Dielectric Behavior and Impedance Spectroscopy of Ba1-xBixTi1-xFexO3 System

Studies on the analysis of impedance spectroscopy of polycrystalline samples with compositions x ≤ 0.20 in the system Ba1-xBixTi1-xFexO3 are made. For this all the samples are prepared using solid state ceramic route. Preliminary X-ray diffraction patterns showed single phase formation of all compositions with tetragonal symmetry for x = 0.02 and cubic symmetry for compositions with x ≥ 0.10. For composition with x = 0.02, the dielectric anomaly at ~100 °C indicates paraelectric to ferroelectric transition. Impedance spectroscopic studies over the temperature range 25 °C to 180 °C have shown the presence of both bulk and grain boundary effects. The bulk conductivity has exhibited Arrehenius type thermally activated hopping process which is supported by ac conductivity behavior as a function of frequency.