Thermodynamics of high entropy oxides

Lead-free perovskite Ba(Fe1/2Nb1/2)O3 (BFN) was prepared by conventional ceramic fabrication technique at 1200 °C/5 h in air atmosphere. The crystal symmetry, space group, and unit cell dimensions were determined from the experimental results using FullProf software whereas crystallite size and lattice strain were estimated from Williamson–Hall approach. X-ray diffraction (XRD) analysis of the compound indicated the formation of a single-phase monoclinic structure with the space group P2/m. EDAX and SEM studies were carried out in order to evaluate the quality and purity of the compound. To find a correlation between the response of the real system and idealized model circuit composed of discrete electrical components, the model fittings were presented using the impedance data. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. The correlated barrier hopping (CBH) model was employed to successfully explain the mechanism of charge transport in BFN.

Structural and impedance spectroscopy analysis of Ba(Fe1/2Nb1/2)O3 ceramic

Microwave assisted solid state reaction method: Investigations on electrical and magnetic properties NiMgZn ferrites

The double perovskite-structured barium iron niobate (BaFe0.5Nb0.5O3, BFN), a lead-free ferroelectric, shows a very high dielectric constant value. We report here the temperature dependent dielectric permittivity, impedance and electric modulus behavior of the BFN ceramic studied between 300 K and 20 K. The phase-pure BFN powder sample was synthesized using a conventional solid state reaction route. The microstructure and the temperature dependent dielectric behavior of the sample are correlated. The dipolar and Maxwell-Wagner (M-W) polarizations of the sample show distinctly different relaxation behaviors at the grain and grain boundary (GB) regions. With a decrease in temperature from 300 K to 20 K, the M-W polarization contribution decreases monotonously. Furthermore, due to the ion-blocking effect originating from the atomic disorder at the GB regions, the impedance of the GB is found to be higher than that of the grains. The grains and GB regions were found to have characteristically very different dipolar relaxation times. Interestingly, the dipolar relaxation time distribution is the broadest at 120 K due to the temperature dependent shift of the dipolar relaxation times at the grain and GB regions. Furthermore, our results confirm that the dipolar polarization mechanism in BFN is associated only with short-range movement of the cations. Our systematic investigation provides a detailed understanding of the low temperature dielectric properties of the BaFe0.5Nb0.5O3 ceramic and makes it potentially attractive for low temperature thermistor applications.

Low temperature dielectric properties and NTCR behavior of the BaFe0.5Nb0.5O3 double perovskite ceramic.

(1-x)PVDF-xBaTiO3 ceramic-polymer composites with x = 0.10, 0.20, 0.30 were prepared using melt growth technique. The crystal symmetry, space group and unit cell dimensions were determined from the XRD data of BaTiO3 using FullProf software, whereas crystallite size and lattice strain were estimated through Williamson-Hall approach. The distribution of BaTiO3 particles in the PVDF matrix were examined using a scanning electron microscope. The correlated barrier hopping model has been applied to the ac conductivity data in order to ascertain the conduction mechanism of charge transport in BaTiO3/PVDF composites. Also, the ac conductivity data have been used to estimate the apparent activation energy, density of states at Fermi level and minimum hopping length. Filler concentration dependent ac conductivity, density of states at Fermi level and minimum hopping length data followed definite trends of exponential growth/decay types of variation.

Electrical Conduction in 0–3 BaTiO3/PVDF Composites

Lead-free perovskite BaY 0.5 Nb 0.5 O 3 was prepared by conventional ceramic technique at 1375 °C/7 h in air atmosphere. The crystal symmetry, space group and unit cell dimensions were derived from the experimental results using FullProf software. XRD analysis of the compound indicated the formation of a single-phase cubic structure with the space group Pm3m. EDAX, X-ray mapping and SEM studies were carried to study the quality and purity of the compound. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. To find a correlation between the response of the real system and idealized model circuit composed of discrete electrical components, the model fittings were presented using the impedance data. Electric modulus studies supported the hopping type of conduction in BaY 0.5 Nb 0.5 O 3 . The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in BaY 0.5 Nb 0.5 O 3 . The ac conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and apparent activation energy of the compound.

Electrical properties of BaY0.5Nb0.5O3 ceramic: Impedance spectroscopy analysis

A new lead-free perovskite ceramic Ba(Bi1/2Nb1/2)O3 was prepared by a conventional ceramic technique at 1185 °C in oxygen atmosphere. X-ray diffraction analysis of the compound indicated the formation of a single-phase monoclinic structure. Dielectric study revealed a diffuse phase transition at 340 °C. Cole–Cole analyses suggested the dielectric relaxation to be of non-Debye type. Electric modulus studies supported the hopping type of conduction in Ba(Bi1/2Nb1/2)O3. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dielectric relaxation in lead-free perovskite Ba(Bi1/2Nb1/2)O3

Lead-free pseudo-binary compounds (1-x)Ba(Fe1/2Nb1/2)O3-xBaTiO3; (0 ≤ x ≤ 1) have been synthesized at 1200C using conventional ceramic technique and characterized by X-ray diffraction, scanning electron microscopy, dielectric and vibration sample magnetometer studies. The crystal structure of the compounds is found to be monoclinic with the space group P2/m except for BaTiO3 for which it is tetragonal (P4/mmm). The incorporation of BaTiO3 significantly reduces the dielectric loss and improve the frequency and temperature stability of the dielectric properties of Ba(Fe1/2Nb1/2)O3. Compound 0.25Ba(Fe1/2Nb1/2)O3-0.75BaTiO3 exhibited a low value of temperature coefficient of capacitance (< 3%) in the working temperature range (up to +85°C), room temperature dielectric constant equal to 282 and low loss tangent (~10 -2 ) which meets the specifications for "Z5D" of Class II dielectrics of Electronic Industries Association. Hence, this composition might be a suitable candidate for capacitor applications. Besides, magnetic studies indicated the possibility of magneto-electric coupling in the system. Copyright © 2014 VBRI press.

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The Structural, Electrical And Magnetic Properties Of Perovskite (1-x)Ba(Fe1/2Nb1/2)O3–xBaTiO3 Ceramics

Lead free perovskite Ba(La1/2Nb1/2)O3 was prepared by conventional ceramic fabrication technique at 1375°C for 7 h in air atmosphere. The crystal symmetry, space group and unit cell dimensions were estimated using Rietveld analysis. X-ray diffraction analysis indicated the formation of a single phase monoclinic structure with space group P2/m. Energy dispersive X-ray analysis and scanning electron microscopy studies were carried to study the quality and purity of the compound. Permittivity data showed low temperature coefficient of capacitance (T CC = 11%) up to 100°C. The circuit model fittings were carried out using the impedance data to find the correlation between the response of real system and idealised model electrical circuit. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in Ba(La1/2Nb1/2)O3. The AC conductivity data were used to ev...

S. Bhagat

Papers

Structural and impedance spectroscopy analysis of Ba(Fe1/2Nb1/2)O3 ceramic

Electrical properties of BaY0.5Nb0.5O3 ceramic: Impedance spectroscopy analysis

Dielectric relaxation in lead-free perovskite Ba(Bi1/2Nb1/2)O3

The Structural, Electrical And Magnetic Properties Of Perovskite (1-x)Ba(Fe1/2Nb1/2)O3–xBaTiO3 Ceramics

Structural and electrical properties of lead free ceramic: Ba(La1/2Nb1/2)O3