Browsing by Author "Kumari, Sapna"

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    Enhanced Curie temperature and superior temperature stability by site selected doping in BCZT based lead-free ceramics
    (Elsevier Ltd, 2022-01-31T00:00:00) Kumari, Sapna; Kumar, Amit; Kumar, Aman; Kumar, V.; Thakur, Vikas N.; Kumar, Ashok; Goyal, P.K.; Gaur, Anurag; Arya, Anil; Sharma, A.L.
    In this work, Bi3+ doped Ba0.98-3x/2BixCa0.02Zr0.02Ti0.976Cu0.008O3 [0 ? x ? 0.03] lead free ceramics, to be employed for structural, dielectric and ferroelectric studies, have been synthesized via conventional solid state reaction method. Rietveld refinement of the X-ray diffraction (XRD) data evidences the existence of a pure perovskite phase with tetragonal symmetry for all ceramics. The Scanning Electron Microscopy (SEM) reveals that the grain size, which is 16.14 ?m for x = 0 reduced to 2.11 ?m for x = 0.03. Dielectric studies demonstrate excellent dielectric behavior with high Curie temperature (TC ?159 �C), high dielectric constant (?r ?834, ?max ? 3146), and a low dielectric loss (tan? ? 0.019), for an optimum value of x = 0.02. The analysis of temperature coefficient of the dielectric permittivity indicates the applicability of these materials in multilayer ceramic capacitors. Impedance studies, conducted to understand the underlying physical mechanisms, are found to be in good agreement with the results of structural and dielectric studies. Furthermore, the ferroelectric measurement confirms the ferroelectric nature for all samples with an energy storage efficiency (?) of ?42% for x = 0.02 composition. � 2022 Elsevier Ltd and Techna Group S.r.l.
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    Role of sintering temperature in tailoring the electrical properties of 0.98KNNS�0.02BNZSH piezoelectric ceramics
    (Springer, 2023-02-16T00:00:00) Kumar, Amit; Kumari, Sapna; Kumar, V.; Kumar, Ashok; Goyal, P.K.; Aggarwal, Sanjeev; Arya, Anil; Sharma, A.L.
    Lead-free 0.98(K0.5Na0.5)(Nb0.96Sb0.04O3)�0.02(Bi0.5Na0.5)(Zr0.8Sn0.1Hf0.1)O3 (0.98KNNS�0.02BNZSH) perovskite ferroelectric ceramics have been designed and prepared through the traditional ceramic fabrication technique. To have an insight on the effects of sintering temperature (in the range from 1020 to 1110��C), the structural, microstructural, dielectric and ferro/piezoelectric properties of 0.98KNNS�0.02BNZSH ceramics are investigated systematically. The structural analysis has revealed a pure perovskite phase for sintering at different temperatures. The rhombohedral (R) and orthorhombic (O) phases coexist for sintering of 0.98KNNS�0.02BNZSH ceramic at 1080��C, while the rhombohedral phase dominates above 1080��C. The grains become more uniform and tightly packed when the sintering temperature is increased from 1020 to 1080��C. However, the grain size and the density have been revealed to be decreased for samples sintered above 1080��C. The conduction behavior of 0.98KNNS�0.02BNZSH ceramics has also been investigated using complex impedance spectroscopy. The optimum values of different dielectric and ferro/piezoelectric parameters for 0.98KNNS�0.02BNZSH ceramics sintered at 1080��C are obtained to be as the following: TC ~ 317��C, ?max ~ 7102, tan? ~ 0.10, ? ~ 4.49�g/cm3, d33 ~ 180 pC/N, and Pr ~ 16.7 �C/cm2. These findings show that crystallizability, density, and electrical properties are significantly influenced by the sintering temperature. � 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
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    Structural, dielectric and ferroelectric properties of Cu2+- and Cu2+/Bi3+-doped BCZT lead-free ceramics: a comparative study
    (Springer, 2021-05-29T00:00:00) Kumari, Sapna; Kumar, Amit; Kumar, V.; Dubey, S.K.; Goyal, P.K.; Kumar, Suresh; Sharma, A.L.; Arya, Anil
    Perovskite-type Ba0.98Ca0.02Zr0.02Ti0.98O3 (BCZT), Ba0.98Ca0.02Zr0.02Ti0.976Cu0.008O3 (BCZTC) and Ba0.9725Bi0.005Ca0.02Zr0.02Ti0.976Cu0.008O3 (BCZTCB) lead-free ceramics were synthesised via solid-state reaction method at a sintering temperature of 1380��C. Effects of CuO and Bi2O3/CuO doping on structural, microstructural, dielectric and ferroelectric properties were investigated systematically. X-ray diffraction technique confirmed the existence of pure perovskite phase with the tetragonal structure in pure and in the doped BCZT ceramics at room temperature. The dielectric analysis demonstrated two anomalies around 24��C and 126��C for BCZT, which were identified as orthorhombic to tetragonal (TO-T) and tetragonal to cubic (TC) phase transition temperature, respectively. The TO-T temperature shifted to below 16��C, while the TC increased to 132��C for the BCZTCB sample. The physical mechanisms of the conduction processes were investigated through impedance spectroscopy, and the values of resistance, conductivity and activation energies associated with the grain and grain boundaries were evaluated. The activation energy was determined to be higher for doped samples than for pure BCZT. Further, the dopant-dependent ferroelectric nature of the ceramic samples was evidenced by the analysis of characteristic hysteresis loop, and a value of remnant polarization (Pr = 4.59�?C/cm2) was obtained for the BCZTCB ceramic sample. Furthermore, the d33 value, which was 54 pC/N for pure BCZT, was determined to be 140 pC/N and 64 pC/N for BCZTC and BCZTCB, respectively. � 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
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    Synthesis, phase confirmation and electrical properties of (1 ? x)KNNS?xBNZSH lead-free ceramics
    (Springer, 2022-02-02T00:00:00) Kumar, Amit; Kumari, Sapna; Kumar, V.; Kumar, Prashant; Thakur, Vikas N.; Kumar, Ashok; Goyal, P.K.; Arya, Anil; Sharma, A.L.
    In the present work, lead-free piezoelectric ceramics (Rx)(K0.5Na0.5)(Nb0.96Sb0.04O3)?x(Bi0.5Na0.5)(Zr0.8Sn0.1Hf0.1)O3 [abb. as (Rx)KNNS?xBNZSH, 0 ? x ? 0.04] were prepared via solid-state sintering technique. The thermal behavior of mixed powders has been investigated for x = 0, 0.02, and 0.04 using TGA-DSC analysis to estimate the calcination temperature. The structural, morphological, dielectric, ferroelectric and piezoelectric properties are analyzed through the appropriate characterization techniques. The X-ray diffraction (XRD) patterns demonstrate a pure perovskite phase structure for all the sintered samples. Further, the coexistence of rhombohedral to orthorhombic (R-O) phase is observed in ceramic sample with x = 0.02. The morphology of all the sintered samples exhibits an inhomogeneous, dense microstructure with the rectangular grain, while for x = 0.02, a relatively homogeneous distribution of grains is observed. BNZSH doping decreases the average grain size from 2.22 to 0.33�?m for x = 0 to x = 0.04, respectively. Owing to the presence of multiple-phase coexistence as well as the improved microstructure and enhanced dielectric properties (dielectric constant ?r = 1080, ?max = 5301; Curie temperature - TC ~ 317��C; dielectric loss - tan? ~ 6%) the ceramics with x = 0.02 has been found to have a large piezoelectric coefficient (d33) of ~180 pC/N, remnant polarization (Pr) ~ 16.7 �C/cm2 and coercive field (Ec) ~ 10.7�kV/cm. We believe it will expand the range of applications for KNN-based ceramics. � 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.