Prakash Gopalan

Dielectric properties of A- and B-site doped BaTiO3(II):La- and Ga-doped solid solutions

Extremely small amounts of codoping La and Ga on the A and B sites of BaTiO3, respectively, resulting in a solid solution of the type Ba1−3xLa2xGa4xTi1−3xO3, have been investigated. The compounds have been prepared by conventional solid-state reaction. The x-ray diffraction (XRD) shows the presence of the tetragonal (P4∕mmm) phase only. The XRD data have been analyzed using the FULLPROF Rietveld refinement package. The compositions have been characterized by dielectric spectroscopy between room temperature and 200°C. The resulting compounds (0⩽x⩽0.008) exhibit a remarkable decrease in Curie temperature as well as a significant enhancement in the dielectric constant.

Impedance and AC conductivity study of nano crystalline, fine grained multiferroic bismuth ferrite (BiFeO3), synthesized by microwave sintering

In this paper, major reduction in sintering time,temperautre and significant improvement over final density of sitnered sample is reported for the microwave sintered nanocrystalline BiFeO3 (BFO) ceramic. Also, different sintering time and temperatures have been used to tailor the grain size and the final density of the resulting BFO ceramics synthesized from phase pure BFO nanoparticles (d ≈10 nm). Microwave sintering resulted in reducing the sintering time substantially (by 1h), and has resulted in submicron sized grains and high resistivity ∼1.8 GΩ-cm. The AC conductivity is seen to follow the Jonscher’s power law behavior, suggesting correlated barrier hopping (CBH) mechanism in the sample. The role of oxygen vacancies at high temperature, due to volatility of bismuth, in dielectric and conductivity behavior is also discussed. Further, the sample displayed dielectric anomaly near magnetic transition temperature (∼180 °C) indicating bearing of magnetic moments on the dielectric properties. Using Impeda...

Study on Ionic and Electronic Transport Properties of Calcium-Doped GdAlO3

Oxygen-permeation measurements were carried out on a Gd 0.85 Ca 0.15 AlO 3-δ specimen in the temperature range of 400-900°C as a function of the oxygen partial pressure from 1.01 X 10 5 to 18.85 Pa. Simultaneously, the open-circuit voltage of the permeation cell and the voltage upon partially short-circuiting the cell over external resistances were measured. As a result, the ionic conductivity of Gd 0.85 Ca 0.15 AlO 3-δ between 650 and 900°C and the electronic conduction parameter p ⊕ of the hole conductivity were obtained as a function of temperature. The electrochemical performance as well as the stability of the electrolyte material were studied by carrying out cell-voltage measurements under Ar + 1000 ppm H 2 (anode) and air (cathode) environments. The present investigations suggest that Gd 0.85 Ca 0.15 AlO 3-δ is predominantly an oxygen-ion conductor with an ionic conductivity slightly below that of yttria-stabilized zirconia.

Na2SO4–Al2O3 composite electrolytes: some interesting observations

Abstract In the Na 2 SO 4 –Al 2 O 3 system, the variation in electrical conductivity with composition and dispersoid size stands in stark contrast to that of most other reported composite systems. Two maxima, instead of one, are observed in the conductivity vs. composition plot, at 5.5 and 35 mol% Al 2 O 3 . Maximum conductivity enhancement is observed for 35 mol% Al 2 O 3 . The increase is about 20 times at 400°C and 450 times at 200°C. Possible conductivity enhancement mechanisms operating in this system are suggested. Surprisingly, the reduction in alumina particle size from 0.5 to 0.004 μm does not bring about any further enhancement in conductivity.

Structural and Electrical Characterization of La and Mn Co-Substituted Bismuth Ferrite Thin Films

Bismuth ferrite thin films with 10% La and 5% Mn (BLFMO) have been deposited using Pulsed laser deposition. It is found that oxygen pressure has pronounced effect on the structural and electrical properties of BLFMO thin films. The leakage current density increases with the oxygen pressure. At 0.007 mbar, the leakage current density is found to be in the order of 10−7A/cm2 at 200 kV/cm. The remnant polarization is 73 μC/cm2 at 200 kV/cm. Fatigue endurance has been studied for optimized film and found that films are almost fatigue free after 108 pulses. There is only 3% change in the polarization up to 106 seconds as revealed by retention test.

Dielectric Properties of La3+ at A Site and Al3+ and Ga3+ Doped at B Site in BaTiO3

In this investigation, the A- and B-site doped BaTiO3 have been investigated. The extremely small concentration of dopant concentration (La3+) at A site with formula Ba(1-3x)La2xTiO3 and (Al3+,Ga3+) B site with formula BaTi(1-3x)Al4xO3 and BaTi(1-3x)Ga4xO3 have been probed using X-ray diffraction (XRD), impedance spectroscopy, dielectric spectroscopy, and differential scanning calorimetry (DSC). The dielectric behavior of doped BaTiO3 has been studied in the temperature range 40 to 200 °C. It has been observed that as La3+ concentration varies from 0.004 to 0.012, the transition temperature of La3+ doped BaTiO3 decrease. In case of Al3+ and Ga3+, the transition temperature is found to increase slightly. The maximum dielectric constant has been observed for Al3+/La3+/Ga3+. The conductivity of doped BaTiO3 has been reported in the temperature range 500 to 300 °C. The activation energies for Al3+ and Ga3+ doped BaTiO3 (x = 0.006) are 0.32 and 0.43 eV, respectively. The types of defects in BaTiO3 have been analyzed on the basis of conductivity data.

Growth and Characterization of Na0.5Bi0.5TiO3 Thin Films with BaTiO3 Buffer Layer (Study of Au/Na0.5Bi0.5TiO3/BaTiO3/Pt Capacitor)

Lead free bilayer capacitor structure has been fabricated as a combination of sodium bismuth titanate (Na0.5Bi0.5)TiO3 (NBT) thin films with barium titanate, (BaTiO3) (BT) buffer layer in situ using pulsed laser deposition (PLD). PLD control parameters have been optimized using Taguchi approach to obtain good quality NBT and BT thin films. It has been observed that dielectric properties of NBT thin films enhanced by inserting BT buffer layer. This improvement in the dielectric properties of NBT thin films have been discussed in relation to the effect of the buffer layer on the structure, microstructure and interface of the NBT/BT multilayer capacitor.

Microstructural Characterization of Ferroelectric Bismuth Ferrite (BiFeO3) Ceramic by Electron Backscattered Diffraction

Ferroelectric BiFeO3 (BFO) is potential candidate for future generation of FeRAM due to its large polarization. However, BFO is very sensitive to secondary phase formation during synthesis because of volatility issues related to Bismuth. Investigation of the microstructure for phase purity is the key as impurities can destroy the desired properties. We have used backscattered electron diffraction to study the microstructure of BFO ceramic. The EBSD results provide a direct evidence of the appearance of secondary phase that XRD could not be detected in XRD.

Effect of Cobalt substitution on the structural, electrical and magnetic properties of BaTiO 3 ceramics

Cobalt doped BaTiO3 (BaTi1-xCoxO3) with x = 0, 5, 7.5, 10% have been synthesized by solid state reaction method and their structural, electrical and magnetic properties have been investigated. Structural characterization show that a multiphase ceramic containing both tetragonal and hexagonal structures are obtained for Co compositions from x = 5% to x = 10%. Ferroelectric and ferromagnetic properties have been observed in all the Co-doped BaTiO3 ceramics at room temperature. The ferromagnetic hysteresis loop at room temperature is due to the formation of oxygen vacancies and their associated exchange interaction. The saturation magnetization (Ms) was 0.010 emu/g for x = 5%. Further, at x = 7.5%, it decreases and again start increasing upto ~ 0.013 emu/g for x = 10% with Cobalt concentration. However, ferroelectric hysteresis loop (P-E) is deteriorated (lossy type) with the increase of Co concentration above x = 5%. The dielectric characterization with frequency has also been carried out for all samples. The dielectric constant decreases with increasing Cobalt concentration.

Effect of Barium Titanate buffer layer on dielectric properties of Sodium Bismuth Titanate thin films grown using Pulsed Laser Deposition

Lead free bilayer capacitor structure has been fabricated as a combination of Sodium Bismuth Titanate, (Na0.5Bi0.5)TiO3 (NBT) thin films with Barium Titanate, (BaTiO3) (BT) buffer layer in situ using Pulsed Laser Deposition (PLD). PLD control parameters have been optimized using Taguchi approach to obtain good quality NBT and BT thin films. In order to understand the effect of buffer layer on the structural and dielectric properties of NBT thin films, 50 nm thickness of BT buffer layer has been grown on Pt coated Si substrate. It has been found that dielectric constant and dielectric loss of NBT thin films is 735 and 0.07 at 1 kHz respectively. It is observed that dielectric properties of NBT thin films enhanced by inserting BT buffer layer. This improvement in the dielectric properties of NBT thin films have been discussed in relation to the effect of the buffer layer on the structure, microstructure and interface of the NBT/BT bilayer capacitor.