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Rai R.,University of Aveiro | Rai R.,Shoolini University of Biotechnology and Management Sciences | Rani R.,Ferroelectric Research Laboratory | Sharma S.,Ferroelectric Research Laboratory | Kholkin A.L.,University of Aveiro
Journal of Alloys and Compounds | Year: 2013

Lead-free piezoceramics (K0.5NaK0.5) 1-2xLixLaxNbO3 (where x = 0.050, 0.055, 0.060, and 0.065) have been fabricated by a conventional sintering technique. The effect of Li and La doping on the phase structure and electrical properties of (K0.5NaK0.5)1-2xLi xLaxNbO3 ceramics was investigated. X-ray diffraction analysis showed that the ceramics possess a perovskite structure with orthorhombic symmetry. A small amount of second phase (K6Li 4Nb10O30, ∼3%) was present in KNLLN ceramics. Ferroelectric-paraelectric phase transition temperature decreases with increase in doping content. La-doping in the ceramics displayed a relative lower loss tangent (tand) from room temperature up to 350 °C. Detailed studies of dielectric and electrical properties indicate that the Curie temperature shifted to lower temperature with the increase in Li and La doping. Moreover, the dielectric maxima dropped down rapidly and the dielectric peaks became extremely broad. The weak dielectric properties for the samples of x = 0.065 can be ascribed to the formation of pseudo-cubic structures at high level of Li and La substitution. The AC conductivity increases with increase in temperature showing a negative temperature coefficient of resistance (NTCR) behavior. The low value of activation energy obtained for the ceramic samples could be attributedto the influence of electronic contribution to the conductivity. © 2013 Elsevier B.V. All rights reserved.


Verma K.,Ferroelectric Research Laboratory | Sharma S.,Ferroelectric Research Laboratory | Sharma D.K.,Ferroelectric Research Laboratory | Kumar R.,Ferroelectric Research Laboratory | Rai R.,University of Aveiro
Advanced Materials Letters | Year: 2012

Ba0.5Sr0.3TiO3 (BST 70/30) nanopowders have been prepared by the modified sol-gel method using barium acetate, strontium acetate and titanium isopropoxide as the precursor. The formation mechanism, phase evolution, and particle size have been investigated using TG/DTA, XRD, and SEM. The fine particles of the nano-powders calcined are homogeneous and well-dispersed and their narrow size distribution is about 15-25 nm. The as-formed gel was dried at 2000 C and then calcined in the temperature range 650°C to 850°C for crystallization. Phase evolution during calcination was studied using X-ray diffraction (XRD) technique which exhibited cubic crystal structure with perovskite phase. Sintering of the pellet was performed at 950°C and the study on the dielectric relaxation and the ac electrical conductivity behavior of modified Barium titanate, Ba0.7Sr0.3TiO3ferroelectric ceramic exhibit that these are thermally activated process. © 2011 VBRI press.


Thakur S.,Shoolini University of Biotechnology and Management Sciences | Rai R.,Shoolini University of Biotechnology and Management Sciences | Sharma S.,Ferroelectric Research Laboratory
Materials Letters | Year: 2015

This report presents the synthesis of NiFexO4 by co-precipitation method and its subsequent characterization by using X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) techniques. XRD results confirm the single cubic spinel phase formation with the average particle size of 10-15 nm. The particle size decreased with variation of iron content, while the lattice parameter increased with the increase in Fe content. By using VSM technique, a significant change in the magnetic properties was observed in NiFexO4 system. It is seen that remnant magnetization MR increased with increasing concentration up to x=2.0 and then decreases for x=2.2. It is observed that as impurity phase percentage increases, the saturated magnetization decreases. The sample with pure phase has a maximum value of magnetization. The saturated magnetization value of nano NiFe2.0O4 sample is 47.5 emu/g and this is lower than that reported for the bulk nickel ferrite (55 emu/g). © 2014 Elsevier B.V. All rights reserved.


Rai R.,University of Aveiro | Valente M.A.,University of Aveiro | Bdikin I.,University of Aveiro | Kholkin A.L.,University of Aveiro | Sharma S.,Ferroelectric Research Laboratory
Journal of Physics and Chemistry of Solids | Year: 2013

Dielectric and magnetic properties of the Bi1-x-yGd xLayFe1-yTiyO3 (x=0.1 and y=0.0, 0.1, 0.2, 0.3 and 0.5) solid solution ceramics have been presented this work. Effects of La substitution on the structural, electrical and ferroelectric properties of Bi1-x-yGdxLayFe 1-yTiyO3 samples have been studied by performing X-ray diffraction and dielectric measurements as well as characterizing M-H hysteresis loop. The results indicate that, when La content exceeds 0.2, the crystal structure of the ceramic samples changes from rhombohedral to tetragonal phase. The maximum ferroelectric transition temperature (Tc) of this system was 190 °C with the dielectric constant peak of 2500 at 100 kHz for y=0.5. With increasing La content, the remanent magnetization increases and the coercive magnetic field decreases. © 2013 Elsevier Ltd.


Rani R.,Ferroelectric Research Laboratory | Sharma S.,Ferroelectric Research Laboratory | Rai R.,University of Aveiro | Kholkin A.L.,University of Aveiro
Solid State Sciences | Year: 2013

Pure (Na0.50K0.50)0.95(Li 0.05Sb0.05Nb0.95)O3 (NKNLS) and CuO doped NKNLS perovskite structured ferroelectric ceramics were prepared by the solid-state reaction method. x wt% of CuO (x = 0.2-0.8 wt%) was added in the NKNLS ceramics. X-ray diffraction patterns indicate that single phase was formed for pure NKNLS while a small amount of second phase (K6Li 4Nb10O30 ∼ 3%) was present in Cu 2+ doped NKNLS ceramics. Dielectric anomalies around the temperatures of 120 °C and 350 °C have been identified as the ferroelectric- paraelectric transition (orthorhombic to tetragonal and tetragonal to cubic) temperatures for pure NKNLS compound. The electrical behavior of the ceramics was studied by impedance study in the high temperature range. Impedance analysis has shown the grain and grain boundary contribution using an equivalent circuit model. The impedance response in pure and Cu2+ doped NKNLS ceramics could be resolved into two contributions, associated with the bulk (∼grains) and the grain boundaries. From the conductivity studies, it is found that activation energies are strongly frequency dependent. The activation energy obtained from dielectric relaxation data may be attributed to oxygen ion vacancies. © 2012 Elsevier Masson SAS. All rights reserved.


Sharma D.K.,Ferroelectric Research Laboratory | Kumar N.,Indian Institute of Technology Kharagpur | Sharma S.,Ferroelectric Research Laboratory | Rai R.,University of Aveiro
Materials Chemistry and Physics | Year: 2013

The near morphotropic phase boundary (MPB) compositions of lead-free piezoelectric ceramics based on sodium bismuth titanate (Na 0.50Bi0.50TiO3: NBT) and barium titanate (BaTiO3: BT) were carefully investigated by conventional high temperature mixed-oxide method. All the ceramics exhibit single phase rhombohedral symmetry. The frequency (100 Hz to 1 MHz) and temperature (Room temperature-500 C) dependence of impedance spectroscopy of (1 - x)Na 0.50Bi0.50TiO3-xBaTiO3 (x = 0.0, 0.06, 0.07 and 0.08) ceramics were investigated by impedance analyzer. The frequency explicit plots of Z″ versus frequency at various temperatures show peaks in the higher temperature range (>400 C). The compounds show dielectric relaxation, which is found to be of non-Debye type and the relaxation frequency shifted to higher side with increase in temperature. The activation energy values obtained for different BT content suggest that the electrical conduction in NBT is mainly due to the mobility of the ionized oxygen defects© 2013 Elsevier B.V. All rights reserved.


Rai R.,University of Aveiro | Coondoo I.,University of Aveiro | Rani R.,Ferroelectric Research Laboratory | Bdikin I.,University of Aveiro | And 2 more authors.
Current Applied Physics | Year: 2013

(1 - x) K 0.5Na 0.5NbO 3 - xLiNbO 3 (where x = 0.0, 5.0, 5.5, 6.0, and 6.5 wt.%) (KNLN) perovskite structured ferroelectric ceramics were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that single phase was formed for pure KNN while a small amount of second phase (K 6Li 4Nb 10O 30, ∼3%) was present in LN doped KNN ceramics. Phase analysis indicated the change in the crystal structure from orthorhombic to tetragonal with increase in LN content. The electrical behavior of the ceramics was studied by impedance spectroscopy technique in the high temperature range. Impedance analysis was performed using an equivalent circuit model. The impedance response in pure KNN and KNLN ceramics could be deconvoluted into two contributions, associated with the bulk (grains) and the grain boundaries. Activation energies for conductivity were found to be strongly frequency dependent. The activation energy obtained from dielectric relaxation data was attributed to oxygen vacancies. From PFM we found that the composition with 6.5 wt.% LN displays stronger piezocontrast as compared to pure KNN implying an evidence of a pronounced piezoelectric coefficient. © 2012 Elsevier B.V. All rights reserved.


Verma K.,Ferroelectric Research Laboratory | Sharma S.,Ferroelectric Research Laboratory
Ceramics International | Year: 2012

Polycrystalline composites of (1 - x) (Ba 0.7Sr 0.3TiO 3)-x(Cu 0.5Cd 0.5Fe 2O 4) (x = 0.15, 0.30, 0.45) were prepared by a modified wet chemical method. X-ray diffraction studies at room temperature confirmed the formation of polycrystalline composite with perovskite-spinel structure. Scanning electron micrographs also suggest polycrystalline microstructure with the grains of unequal size distributed throughout the pellet samples. Dielectric studies of the composites reveal that the effect of ferrite in the composites is to shift the ferroelectric-non-ferroelectric phase transition to higher temperature side. Complex impedance spectroscopy analysis indicated negative temperature coefficient of resistance behavior identical to semiconductors. The activation energy calculated from the temperature dependence of conductivity pattern shows that the conduction process can occur due to the hopping of electrons between Fe 3+ and Fe 2+, leading to the contribution of both single and doubly-ionized oxygen vacancies. © 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.


Verma K.,Ferroelectric Research Laboratory | Sharma S.,Ferroelectric Research Laboratory
Physica Status Solidi (B) Basic Research | Year: 2012

Polycrystalline composites of (1-x) (Ba 0.7Sr 0.3TiO 3)-x(Ni 0.5Zn 0.5Fe 2O 4) (x=0.00, 0.45, 1.00) were prepared by a modified wet chemical method followed by a high-temperature sintering process. X-ray diffraction (XRD) studies at room temperature confirmed the formation of perovskite-spinel structure. Scanning electron micrographs suggest polycrystalline microstructure with grains of unequal size distributed throughout the samples. Dielectric studies of the composites reveal that the effect of ferrite in the composites is to shift the ferroelectric-non-ferroelectric phase transition to the higher temperature side with a broadened Curie temperature transition. Complex impedance spectroscopy analysis indicated negative temperature coefficient of resistance behavior, identical to semiconductors. The conduction at low temperature is due to impurities, whereas at higher temperature it is due to polaron hopping. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Rani R.,Ferroelectric Research Laboratory | Sharma S.,Ferroelectric Research Laboratory | Rai R.,University of Aveiro | Kholkin A.L.,University of Aveiro
Materials Research Bulletin | Year: 2012

Ceramic samples of [Na 0.5K 0.5] 1 - x(Li) x(Sb) x(Nb) 1 - xO 3 (NKNLS) (x = 0.04-0.06) were prepared by high temperature solid-state reaction method. X-ray diffraction analysis of the powder samples suggests the formation of a single-phase material with transformation from orthorhombic to tetragonal crystal structure with increase in Sb content. Dielectric studies show a diffuse phase transition about 100 °C and another phase ferroelectric-paraelectric transition at 330 °C. Polarization vs. electric field (P-E) hysteresis studies show maximum remanent polarization (Pr ∼ 0.66 C m -2) for composition x = 0.05. AC conductivity in the compound increases with increase in temperature which may be attributed due to oxygen vacancies and show negative temperature coefficient of resistance (NTCR) effect. © 2011 Elsevier Ltd. All rights reserved.

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