Vijayeta Pal

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.

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.

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.

Dielectric and Ferroelectric Properties of Lead-Free Ceramic System

Lead-free specimens of [-BaTiO3] (BLNLT-BT, where , , and , 0.02, 0.04, and 0.06) ceramic system were synthesized by a semiwet technique. In the present study, we have investigated the effect of Ba on the structure, morphology, and dielectric, ferroelectric, and piezoelectric properties of BLNLT system. The XRD patterns of all the specimens showed rhombohedral structure at room temperature. Field emission scanning electron microscopy images (FE-SEM) showed grain growth inhibition with Ba content in BLNLT system. The temperature dependence of dielectric constant revealed that the temperature of maximum dielectric constant “” and depolarization temperature “” decreased for the sample and showed high value of dielectric constant with low dielectric loss. These samples exhibited nonlinear behaviour of hysteresis loop. The values of dielectric constant (), dissipation factor (tan δ), piezo charge coefficient (), remnant polarization (), and coercive field () for the composition were 1495, 0.06, 20 pC/N, 5 μC/cm2, and 10.5 kV/cm, respectively.

Effect of Processing on Synthesis and Dielectric Behavior of Bismuth Sodium Titanate Ceramics

An effort has been made to synthesize polycrystalline (abbreviated as BLNT) system with compositions x = 0, 0.02, and 0.04 by novel semiwet technique. Preparation of A-site oxides of BLNT for composition x = 0 was optimized using two precursor solutions such as ethylene glycol and citric acid. The XRD patterns revealed that the sample prepared by ethylene glycol precursor solution has single phase perovskite structure with a rhombohedral symmetry at RT as compared to the sample prepared by citric acid. Ethylene glycol precursor has been found to play a significant role in the crystallization, phase transitions, and electrical properties. The studies on structure, phase transitions, and dielectric properties for all the samples have been carried out over the temperature range from RT to 450°C at 100 kHz frequency. It has been observed that two phase transitions (i) ferroelectric to antiferroelectric and (ii) antiferroelectric to paraelectric occur in all the samples. All samples exhibit a modified Curie-Weiss law above Tc. A linear fitting of the modified Curie-Weiss law to the experimental data shows diffuse-type transition. The dielectric as well as ferroelectric properties of BLNT ceramics have been found to be improved with the substitution of La elements.

Effect of Fe doping on structural and impedance properties of PZTFN ceramics

An attempts have been made to synthesis the ceramics Pb1-3x/2 Fex(Zr0.52Ti0.48)1-5y/4 NbyO3 abbreviated as (PFZTN) for x = 1-6 mol% and y = 5.5 mol% by a semi-wet route. In the present paper, we have investigated the effect of Fe doping on structural and electrical properties of the PFZTN ceramics. X-ray diffraction (XRD) patterns reveal that PFZTN ceramics are single phase in nature. However, for x = 0.05 and 0.06, a secondary phase appears as discernible from the XRD profiles. Rietveld analysis of the powder diffraction data shows the presence of coexistence of tetragonal (P4mm space group) and rhombohedral phases (R3c space group) occurs near the morphotropic phase boundary (MPB) at x ≥ = 0.05. The log-log plots show that the conductivity increases with increase of temperature. The ac conductivity becomes sensitive at high frequency region and shifted towards higher frequency side with increasing temperature. It is observed that the activation energy (Ea) decreases with increasing frequency. This compl...