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Ashok Kumar - One of the best experts on this subject based on the ideXlab platform.
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anomalous change in leakage and displacement currents after electrical poling on lead free ferroelectric ceramics
Applied Physics Letters, 2015Co-Authors: Ashok Kumar, Hitesh Borkar, Monika Tomar, Vinay Gupta, J F ScottAbstract:We report the polarization, displacement current, and leakage current behavior of a trivalent nonpolar cation (Al3+) substituted lead free ferroelectric (Na0.46Bi0.46−xAlxBa0.08)TiO3 (NBAT−BT) (x = 0, 0.05, 0.07 and 0.10) Electroceramics with tetragonal phase and P4 mm space group symmetry. Almost, three orders of magnitude decrease in leakage current were observed under electrical poling, which significantly improves microstructure, polarization, and displacement current. Effective poling neutralizes the domain pinning, traps charges at grain boundaries and fills oxygen vacancies with free charge carriers in matrix, thus saturated macroscopic polarization in contrast to that in unpoled samples. E-poling changes “bananas” type polarization loops to real ferroelectric loops.
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anomalous change in leakage and displacement currents after electrical poling on lead free ferroelectric ceramics
arXiv: Materials Science, 2015Co-Authors: Ashok Kumar, Hitesh Borkar, Monika Tomar, Vinay Gupta, J F ScottAbstract:We report the polarization, displacement current and leakage current behavior of a trivalent nonpolar cation Al cation substituted lead free ferroelectric NBT-BT Electroceramics with tetragonal phase and P4mm space group symmetry. Nearly three orders of magnitude decrease in leakage current were observed under electrical poling, which significantly improves microstructure, polarization, and displacement current. Effective poling neutralizes the domain pinning, traps charges at grain boundaries and fills oxygen vacancies with free charge carriers in matrix, thus saturated macroscopic polarization in contrast to that in upoled samples. E-poling changes bananas type polarization loops to real ferroelectric loops.
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room temperature lead free relaxor antiferroelectric Electroceramics for energy storage applications
RSC Advances, 2014Co-Authors: Hitesh Borkar, Monika Tomar, Vinay Gupta, V N Singh, Bhanu Pratap Singh, Ashok KumarAbstract:Round the globe, scientific communities have been searching for new materials for “green” energy, producing efficiently both high power as well as high energy density. Relaxor ferroelectrics (RFEs) have shown immense potential to achieve this goal. We report fabrication of [Na0.42Bi0.44Al0.06Ba0.08)TiO3 (NBAT–BT)], a lead-free-relaxor antiferroelectric ceramic, via a conventional solid-state reaction method. A small fraction of trivalent cations (Al3+) doping at Na1+/Bi3+ sites develop anti-polar phase in the ferroelectric matrix which in turn changes its functional properties. Rietveld refinement suggests the existence of both tetragonal and rhombohedral phases which is well supported by d-spacing values obtained in high resolution transmission electron microscopy (HRTEM) studies. Elemental analysis confirms the stoichiometry of the system and matches the starting composition well within the experimental uncertainty (±10%) of secondary electron microscopy (SEM) and HRTEM data. Raman spectra suggest the substitution of Al3+ cation at an A-site sublattice. Temperature-dependent dielectric spectra show frequency dependent dielectric dispersion near 80–110 °C, high dielectric loss at high probing frequency, and a non-linear Vogel–Fulcher relation, substantiating the relaxor–antiferroelectric (r-AFE) nature of NBAT–BT. A second order diffuse anti/ferro-electric to paraelectric phase transition near 230–240 °C was observed which follows a modified Curie–Weiss law. The energy density was calculated from polarization–electric field (P–E) loops and dielectric–electric field (e–E) plot. The values were in the range of 0.4–0.6 J cm−3, which is reasonably good for bulk polar material. NBAT–BT shows a much thinner AFE hysteresis above its relaxor FE phase transition; that favors the enhanced energy storage capacity at elevated temperature in the depolarized paraelectric region.
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characterization of electrical behaviour of si modified basno3 Electroceramics using impedance analysis
Journal of Materials Science, 2007Co-Authors: Ashok Kumar, R N P ChoudharyAbstract:The compounds BaSn1−xSixO3 (x = 0–15 mol%) have been prepared by high temperature solid-state reaction route. Powder X-ray diffraction pattern of the samples reveal the formation of a single phase solid solution. It was found that single phase compositions have a cubic crystal structure similar to that of pure barium stannate at room temperature. The a.c. impedance analysis has been carried out in the frequency range 100 Hz–1 MHz for temperature ranging from 300 K to 750 K. Analysis of a.c. impedance data using the complex impedance plane gives the a.c. and d.c. resistance of negative temperature resistance of coefficient (NTCR) Electroceramics. Complex impedance plane and complex electric modulus formalism are employed to determine the inhomogeneous nature of the Electroceramics. This reveals the presence of single elements in the equivalent circuit at elevated temperature. Grain effects are more prominent than that of grain boundary effect at elevated temperature in the material matrix. The electrical conductivity increases sharply with rise in temperature at elevated temperature due to the thermally activated cations. Master modulus analysis provided an evidence of non-exponential type conductivity relaxation occurring in the materials at higher temperatures.
R N P Choudhary - One of the best experts on this subject based on the ideXlab platform.
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fabrication and characterization of lafeo3 batio3 Electroceramics
Materials Chemistry and Physics, 2018Co-Authors: Sushrisangita Sahoo, Satyabati Das, P K Mahapatra, R N P ChoudharyAbstract:Abstract The structural, electrical and multiferroic characteristics of (Ba1-xLax) (Ti1-xFex)O3 (i.e., (1-x) BaTiO3-xLaFeO3) with (x = 0.0–0.5) were investigated. The samples prepared through a chemico-thermal route were found to crystallize in a tetragonal structure similar to that of its parent BaTiO3. Elemental content, surface morphology and vibrational characteristics (from Raman spectra) of the samples were also analyzed. The temperature dependence of dielectric characteristics of all the materials has been studied using a multi-peak Gaussian model. The dielectric peaks are attributed to the magnetic transitions of LaFeO3 and the ferroelectric-paraelectric transition of BaTiO3. The existence of multiple transitions in (Ba1-xLax) (Ti1-xFex)O3 compounds leads to higher values of dielectric constant in a wide range of temperature. Due to the high dielectric or tangent loss of the materials with higher x content, these materials might be suitable for use as microwave absorber. The relaxation and conduction mechanism of all the materials have been investigated. The multiferroic characteristics of the samples have been analyzed with room temperature P-E, M − H and M-E plot.
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dielectric and electrical properties of na2pb2la2w2ti4ta4o30 Electroceramics
Journal of Advanced Ceramics, 2012Co-Authors: Piyush R Das, S Behera, R Padhee, P Nayak, R N P ChoudharyAbstract:The polycrystalline sample of complex tungsten-bronze type compound (Na2Pb2La2W2Ti4Ta4O30) was prepared by a high-temperature solid-state reaction technique. Room temperature preliminary structural study using X-ray diffraction (XRD) data exhibits the formation of a single-phase new compound. The SEM micrograph of the compound exhibits non uniform rectangular grains distributed throughout the sample surface. Detailed studies of dielectric parameters (ɛr, tan δ) as a function of temperature and frequency, and P-E hysteresis (spontaneous polarization) confirmed the existence of ferroelectricity in the material. Complex impedance spectroscopy analysis, carried out as a function of frequency at different temperatures, established a correlation between the microstructure and electrical properties of the material. The electrical relaxation process occurring in the material is temperature dependent. The activation energy found from the Arrhenius plot that the conduction process in the material is of mixed type. The nature of frequency dependence of ac conductivity suggests that the material obeys Jonscher’s universal power law.
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structural dielectric and electrical properties of dysprosium based new complex Electroceramics
Journal of Materials Science: Materials in Electronics, 2012Co-Authors: R Padhee, Piyush R Das, B N Parida, R N P ChoudharyAbstract:The polycrystalline sample of K2Pb2Dy2W2Ti4Nb4O30 was synthesized by high—temperature solid—state reaction method (calcinations temperature ~1,050 °C and sintering temperature ~1,075 °C). The phase formation of the desired compound was confirmed by preliminary X-ray structural analysis. The scanning electron micrograph shows uniform plate and rod like grain distribution throughout the surface of the sample without much pores. Detailed studies of the nature of (1) variation of dielectric parameters with temperature (27–480 °C) and frequency (1 kHz–5 MHz) and (2) polarization (at three different temperatures) confirmed the existence of ferroelectricity in the material, with phase transition occurring at 316 °C. The temperature dependence of electrical parameters (impedance, modulus, conductivity, etc.) of the material exhibits a strong correlation between its micro-structure (i.e., bulk, grain boundary, etc.) and electrical properties. The nature of temperature dependent dc conductivity follows the Arrhenius equation, and reveals the negative temperature coefficient of resistance (NTCR) behaviour of the material. The material obeys Jonscher’s universal power law which is evident from the graphs of frequency dependence of ac conductivity.
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structural thermal and electrical characterization of ndlimo2o8 Electroceramics using impedance spectroscopy
Journal of Physics and Chemistry of Solids, 2012Co-Authors: Sanjaya Brahma, R N P Choudhary, S A ShivashankarAbstract:We report electrical property of a polycrystalline NdLiMo2O8 ceramics using complex impedance analysis. The material shows temperature dependent electrical relaxation phenomena. The d.c. conductivity shows typical Arrhenius behavior, when observed as a function of temperature. The a.c. conductivity is found to obey Jonscher's universal power law. The material was prepared in powder form by a standard solid-state reaction technique. Material formation and crystallinity have been confirmed by X-ray diffraction studies. Impedance measurements have been performed over a range of temperatures and frequencies. The results have been analyzed in the complex plane formalism and suitable equivalent circuits have been proposed in different regions. The role of bulk and grain boundary effect in the overall electrical conduction process is discussed with proper justification. (C) 2011 Elsevier Ltd. All rights reserved.
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characterization of electrical behaviour of si modified basno3 Electroceramics using impedance analysis
Journal of Materials Science, 2007Co-Authors: Ashok Kumar, R N P ChoudharyAbstract:The compounds BaSn1−xSixO3 (x = 0–15 mol%) have been prepared by high temperature solid-state reaction route. Powder X-ray diffraction pattern of the samples reveal the formation of a single phase solid solution. It was found that single phase compositions have a cubic crystal structure similar to that of pure barium stannate at room temperature. The a.c. impedance analysis has been carried out in the frequency range 100 Hz–1 MHz for temperature ranging from 300 K to 750 K. Analysis of a.c. impedance data using the complex impedance plane gives the a.c. and d.c. resistance of negative temperature resistance of coefficient (NTCR) Electroceramics. Complex impedance plane and complex electric modulus formalism are employed to determine the inhomogeneous nature of the Electroceramics. This reveals the presence of single elements in the equivalent circuit at elevated temperature. Grain effects are more prominent than that of grain boundary effect at elevated temperature in the material matrix. The electrical conductivity increases sharply with rise in temperature at elevated temperature due to the thermally activated cations. Master modulus analysis provided an evidence of non-exponential type conductivity relaxation occurring in the materials at higher temperatures.
Guangzhi Dong - One of the best experts on this subject based on the ideXlab platform.
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strain properties of 1 x bi0 5na0 4k0 1tio3 xbi mg2 3ta1 3 o3 Electroceramics
Ceramics International, 2020Co-Authors: Guangzhi Dong, Huiqing Fan, Yuxin Jia, Huan Liu, Weijia WangAbstract:Abstract A ternary solid solution of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–Bi(Mg2/3Ta1/3)O3 (BNKT-xBMT) lead-free Electroceramics was synthesized by a solid-state reactive sintering technique. The electrostrain, dielectric, and ferroelectric properties as well as the impedance characteristics and the microstructure were systematically assessed. With the increase of BMT, the BNKT-xBMT ceramics gradually transformed from non-ergodic relaxor phase to ergodic relaxor phase, manifested as the ferroelectric-to-relaxor temperature (TF-R) shifts towards below room temperature. Additionally, the ferroelectric hysteresis curves became pinched, and the strain curve changed from butterfly-shaped into sprout-shaped. At the ergodic relaxor composition of x = 0.04, a large electrostrain value (S = 0.4%; under an electric field of 60 kV/cm, d33* = 632 pm/V) was achieved, which is mainly attributed to the electric-field-induced transition from the ergodic relaxor phase to the ferroelectric phase.
Eliana N. S. Muccillo - One of the best experts on this subject based on the ideXlab platform.
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Electric field assisted sintering of Electroceramics and in situ analysis by impedance spectroscopy
Journal of Electroceramics, 2017Co-Authors: Reginaldo Muccillo, Eliana N. S. MuccilloAbstract:Since the first report several years ago on pressureless sintering of yttria-stabilized zirconia with several seconds at relatively low temperatures by application of an electric field, an increasing number of scientific reports have been published on sintering ion conducting, semiconducting and insulating polycrystalline Electroceramics. The electric field-assisted sintering consists in applying an electric field either during heating up or under isothermal conditions at temperatures well below the ones applied during conventional sintering. Besides the lower temperatures, shorter times are required to achieve full densification without considerable grain growth, evidencing the potential of this technique for obtaining functional Electroceramics with improved mechanical and electrical properties at lower costs. Even though some mechanisms have been suggested, the description of the phenomenon at the microscopic level leading to full densification with seconds remains a challenge. We report in situ electrochemical impedance spectroscopy of an ionic conductor (ZrO_2: 8 mol% Y_2O_3), a proton conductor (BaCe_0.8Zr_0.1Y_0.1O_3-δ) and a semiconductor (SnO_2: 0.5 mol% MnO_2) performed during conventional and electric field-assisted sintering experiments. Attention is also directed on the description of the experimental setups and procedures and to the evaluation of microstructural details by scanning electron microscopy. The analysis of the in situ impedance spectroscopy diagrams under heating (before either conventional or electric field-assisted sintering) and under cooling (after) provides evidence of densification with pore elimination and welding of grains. Prospects for future experimental and simulation research work are outlined.
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light emission during electric field assisted sintering of Electroceramics
Journal of The European Ceramic Society, 2015Co-Authors: Reginaldo Muccillo, Eliana N. S. MuccilloAbstract:Abstract Electric field-assisted sintering has been shown to occur in ion, electron conducting as well as in insulating polycrystalline ceramics. Considerable linear shrinkage with microstructure control at temperatures lower than the conventionally utilized has been attained mainly in oxide ion conducting zirconia-based solid electrolytes. Some mechanisms, based on localized Joule heating and enhancement of defects diffusion, have been set forth to explain the sudden volume reduction in those ceramics. The results here reported contribute to the understanding of what happens during electric field-assisted sintering, by evidencing the occurrence of light emission simultaneously to the quasi instantaneous specimen shrinkage. An experimental setup with an optical fiber inserted in a dilatometer furnace allowed for light emission detection simultaneously to the electric current pulse in zirconia-yttria and also in tin dioxide specimens upon electric field-assisted sintering.
Weijia Wang - One of the best experts on this subject based on the ideXlab platform.
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strain properties of 1 x bi0 5na0 4k0 1tio3 xbi mg2 3ta1 3 o3 Electroceramics
Ceramics International, 2020Co-Authors: Guangzhi Dong, Huiqing Fan, Yuxin Jia, Huan Liu, Weijia WangAbstract:Abstract A ternary solid solution of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–Bi(Mg2/3Ta1/3)O3 (BNKT-xBMT) lead-free Electroceramics was synthesized by a solid-state reactive sintering technique. The electrostrain, dielectric, and ferroelectric properties as well as the impedance characteristics and the microstructure were systematically assessed. With the increase of BMT, the BNKT-xBMT ceramics gradually transformed from non-ergodic relaxor phase to ergodic relaxor phase, manifested as the ferroelectric-to-relaxor temperature (TF-R) shifts towards below room temperature. Additionally, the ferroelectric hysteresis curves became pinched, and the strain curve changed from butterfly-shaped into sprout-shaped. At the ergodic relaxor composition of x = 0.04, a large electrostrain value (S = 0.4%; under an electric field of 60 kV/cm, d33* = 632 pm/V) was achieved, which is mainly attributed to the electric-field-induced transition from the ergodic relaxor phase to the ferroelectric phase.