Maya Verma

Bio: Maya Verma is an academic researcher from University of Delhi. The author has contributed to research in topics: Dielectric & Materials science. The author has an hindex of 4, co-authored 7 publications receiving 76 citations.

Influence of La doping on structural and dielectric properties of SrBi2Nb2O9 ceramics

Abstract: Lanthanum doped SrBi2Nb2O9 ceramics with the chemical formula SrBi2−xLaxNb2O9 (SBLN) (x=0–05) have been prepared through conventional solid state route X-ray diffraction reveals the shrinkage of unit cell of strontium bismuth niobate with incorporation of La3+ dopant, having no lone pair electrons Shifting of Raman phonon modes indicates the reduced rattling space of NbO6 octahedra with increase in La doping concentration Further, the softening of lowest frequency phonon mode with increasing x in SBLN shows the transition from ferroelectric to paraelectric at room temperature The dielectric properties for all the compositions are studied as a function of temperature (25 to 500 °C) over the frequency range of 10 kHz–1 MHz With increase in lanthanum doping concentration the phase transition becomes diffused and transition temperature gets shifted toward lower temperature A phase transition from normal ferroelectric to paraelectric has been observed via relaxor-type ferroelectrics with increase in x The frequency dependence of transition temperature was studied in terms of Vogel–Fulcher relation for SBLN (x=04)

Dielectric and Ferroelectric Properties of SrBi2Nb2O9 and SrBi1.9La0.1Nb2O9 Ceramics

Abstract: SrBi2Nb2O9 (SBN) and SrBi1.9La0.1Nb2O9 (SBLN) have been prepared through conventional solid state route. The crystallographic orientation of the prepared ceramics was investigated using x-ray diffraction. FTIR spectroscopy indicate the growth of single-phase layered perovskite material. The dielectric properties of prepared ceramics are studied as a function of frequency (10 KHz–1 MHz) at different temperatures (25–500°C). The phase transition temperature of SrBi2Nb2O9 ceramic was found to decrease from 420°C to 395°C with La (10%) doping. A slight decrease in the value of dc conductivity at 500°C from 3.82 × 10−6 to 2.28 × 10−6 Ω−1cm−1 was observed with substitution of La at the Bi-site. The power law behavior of ac conductivity is analyzed as a function of frequency at different temperatures.

Ecotoxicology of Heavy Metals: Sources, Effects and Toxicity

Abstract: The aim of this work is based on assessment of heavy metal pollution in aquatic ecosystem. HMs are ubiquitous in nature and they emanate from nature as well as anthropogenic sources. In past few years, due to continuous discharge from sewage plants and industries, contamination of water bodies has increased tremendously. In recent few years, HMs have received a significant awareness. Basically toxicity of HMs depends upon the embodiment and course of manifestations. They cause interruption in intracellular homeostasis, damage to cellular components through free radicals. This review highlights the necessity for development of mechanism or strategies to overcome metal exposure and to identify substances that devote significantly to overcome their toxic effects within living organisms’ body.

Phase evolution of strontium bismuth niobate ceramics by conventional solid-state reaction method

Abstract: In the present study, formation of single-phase Strontium Bismuth Niobate (SBN) composition is investigated and the phase evolution is understood by studying the reaction mechanism between the raw materials and their combinations. The ceramics compositions were prepared using conventional solid-state reaction method. TG/DTA studies of all the constituents of SBN and the combination of its components have been carried out. X ray diffraction studies reveal the evolution of different phases among the raw powders thermally treated in different temperature ranges. FTIR studies reveal how different phases evolve as a function of calcination temperature. In the present study, an attempt is made to understand the effect of thermal treatment on the reaction mechanism for the formation of single-phase SBN.

The vibrational spectrum of calcite (CaCO3): an ab initio quantum-mechanical calculation Note: Theoretically derived structure

Abstract: The vibrational spectrum of calcite (CaCO3) is evaluated at an ab initio periodic quantum-mechanical level by using the CRYSTAL package. A localized basis set of Gaussian-type functions and the B3LYP hybrid Hamiltonian are adopted. The dynamical matrix is obtained by differentiating numerically the analytical first derivatives of the energy. The accuracy with respect to all computational parameters is documented. The calculated frequencies are compared with available IR and RAMAN data (16 and 5 peaks, respectively), the mean absolute error being less than 12 cm−1 (frequencies range from 100 to 1600 cm−1). Overall, the agreement with experiment is very satisfactory, and shows that simulation can produce at a relatively low cost the full spectra of crystalline compounds of mineralogical interest.

High temperature Aurivillius piezoelectrics: the effect of (Li, Ln) modification on the structure and properties of (Li, Ln)0.06(Na, Bi)0.44Bi2Nb2O9 (Ln = Ce, Nd, La and Y)

Abstract: High temperature Aurivillius piezoelectrics, (Li, Ln)0.06(Na, Bi)0.44Bi2Nb2O9 (NBN-LiLn), with Li and Ln (Ce, Nd, La and Y) co-substitution at the A site, were prepared using a solid-state reaction process. Taking cation disordering between A site and the (Bi2O2)2+ layers into consideration, the crystal structure of (Li, Nd)0.06(Na, Bi)0.44Bi2Nb2O9 (NBN-LiNd) was refined by using the Rietveld method with powder X-ray diffraction, which was confirmed to be a two-layer Aurivillius oxide with an orthorhombic space group, A21am [a = 5.48666(9) A, b = 5.46046(8) A, c = 24.9122(4) A and Z = 4], at room temperature. LiNd substitution induced a decrease in cation disorder and an increase in orthorhombic distortion. The ferroelectric to paraelectric phase transition temperature (Tc) of the NBN-LiLn (Ln = Ce, Nd, La and Y) ceramics ranged from 751 to 842 °C and the Tc increased as the radii of the Ln3+ (Ce3+, Nd3+, La3+ and Y3+) was decreased. The NBN-LiCe and NBN-LiNd had a d33 of 31 and 29 pC N−1, respectively, which is much higher than the reported d33 values of other Aurivillius ceramics with a high Tc (Tc > 650 °C, d33 < 20 pC N−1). With increasing annealing temperature, a significant degradation in d33 was observed for NBN-LiCe, while no drop in d33 was observed up to 650 °C for NBN-LiNd. The inhomogeneous domain structures determined the dissimilar piezoelectric behaviors of NBN-LiCe and NBN-LiNd.

Effect of tungsten doping in bismuth-layered Na0.5Bi2.5Nb2O9 high temperature piezoceramics

Abstract: The effects of W6+ doping for B site on the structural and electrical properties of Na0.5Bi2.5Nb2O9-based ceramics were studied. It shows a trend of preferable orientation growth along c-axis and the Curie point (Tc) decreases slightly from 792 to 761 °C with the increasing W6+ amount. The electrical resistivity of Na0.5Bi2.5Nb2O9-based ceramics increases as much as about two orders of magnitude and the piezoelectric constant d33 is significantly improved from 10.5 to 21.8 pC/N by W6+ modification. The composition of Na0.5Bi2.5Nb1.99W0.01O9 with a high Tc (792 °C), very good temperature stability up to ∼0.96Tc, a large d33 of 17.9 pC/N and sufficient high resistivity, is an excellent candidate for high temperature piezoelectric applications.

Ferroelectric phase transitions in new Aurivillius oxides: Bi2+2xSr1−2xNb2−xScxO9

Abstract: A new series of ferroelectric Aurivillius oxides containing Sc3+ in the B site in stoichiometric compositions, Bi2+2xSr1−2xNb2−xScxO9 (x = 005, 010, 015, 020), were synthesized by a standard solid state method and characterized by powder X-ray diffraction, dielectric and ferroelectric measurements The ferroelectric to paraelectric phase transition temperature (Tc) obtained from dielectric measurements range from 430–731 °C Crystal structure refinement on Bi22Sr08Nb19Sc01O9 (I) using powder X-ray diffraction data revealed that I crystallizes in polar space group, A21am (a = 55083(4) A, b = 55025 (4) A, and c = 251741(11) A; V = 76301 (9) A3), at room temperature I adopts non-polar space group, I4/mmm, at 550 °C (Tc from dielectric measurement for I is 528 °C) Polarization vs electric field measurements on I, showed that the saturation and remanent polarizations are 118 μC cm−2 and 74 μC cm−2 respectively In addition, the correlation of Tc, with tolerance factors are discussed and, with nd0 configurations are explored