arXiv subjects

Parasharam M. Shirage

Publications and source records attributed to Parasharam M. Shirage.

At least 19 recordsLinked to original sources

arXiv2017

Growth of transparent Zn1-xSrxO films by facile wet chemical method: Effect of Sr doping on the structural, optical and sensing properties

Sr doped ZnO nanorods thin films are prepared using wet chemical technique on transparent flexible substrate. Effect of Sr doping on structural and optical properties of ZnO is systematically investigated. The sensing property of the ZnO is enhanced by Sr doping and imitates as a promising material for future toxic and flammable gas sensor applications as well as for optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2017

Search for Origin of Room Temperature Ferromagnetism Properties in Ni doped ZnO Nanostructure

The origin of room temperature (RT) ferromagnetism (FM) in Ni doped ZnO samples are systematically investigated through physical, optical, and magnetic properties of nanostructure, prepared by simple low-temperature wet chemical method. Reitveld refinement of X-ray diffraction pattern displays an increase in lattice parameters with strain relaxation and contraction in Zn/O occupancy ratio by means of Ni-doping. Similarly scanning electron microscope demonstrates modification in the morphology from nanorods to nanoflakes with Ni doping, suggests incorporation of Ni ions in ZnO. More interestingly, XANES (X-ray absorption near edge spectroscopy) measurements confirm that Ni is being incorporated in ZnO as Ni2+. EXAFS (Extended X-ray Absorption Fine Structure) analysis reveals that structural disorders near the Zn sites in the ZnO samples upsurges with increasing Ni concentration. Raman spectroscopy exhibits additional defect driven vibrational mode at 275 cm-1, appeared with Ni-doped sample only and the shift with broadening in 580 cm-1 peak, which manifests the presence of the oxygen vacancy (VO) related defects. Moreover, in photoluminescence (PL) spectra we observed peak appears at 524 nm, indicates the presence of singly ionized VO+, which may activate bound magnetic polarons (BMPs) in dilute magnetic semiconductors (DMSs). Magnetization measurements indicate weak ferromagnetism at RT, which rises with increasing Ni consolidation. It is therefore proposed that effect of the Ni-ions as well as the inherent exchange interactions rising from VO+ assist to produce BMPs, which are accountable for the RT-FM in Zn1-xNixO (0<x<0.125) system.

cond-mat.mtrl-sci↗

arXiv2017

Sr- and Ni-doping in ZnO nanorods synthesized by simple wet chemical method as excellent materials for CO and CO2 gas sensing

In this study, the effect of Sr- and Ni-doping on microstructural, morphological and sensing properties of ZnO nanorods has been investigated. Nanorods with different Sr and Ni loadings were prepared using a simple wet chemical method and characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) analysis. XRD data confirmed that Sr- and Ni-doped samples maintainsthe wurtzite hexagonal structure of pure ZnO. However, unlikes Sr, Ni doping modifies the nanorod morphology, increases the surface area (SA) and decreases the ratio of IUV/Igreen photoluminescence peak to a greater extent. Sensing tests were performed on thick films resistive planar devices for monitoring CO and CO2, as indicators of indoor air quality.The effect of the operating temperature, nature and loading of dopant on the sensibility and selectivity of the fabricated sensors towards these two harmful gases were investigated. The gas sensing characteristics of Ni- and Sr-doped ZnO based sensors showed a remarkable enhancement (i. e. the response increased and shifted towards lower temperature for both gases) compared to ZnO-based one, demonstrating that these ZnO nanostructures are promising to fabricate sensor devices for monitoring indoor air quality.

cond-mat.mtrl-sci↗

arXiv2017

Synthesis of Ni doped ZnO nanostructures by low temperature wet chemical method and their enhanced field emission properties

In this study, we report the enhancement in field emission (FE) properties of ZnO nanostructure by Ni doping at the base pressure of ~1 x 10-8 mbar, which were grown by the simple wet chemical process. ZnO nanostructure shows single crystalline wurtzite structure up to Ni 10% doping. FESEM represents change in the nanostructure morphology from thick nanoneedles to nanoflakes via thin nanorods with increase in Ni doped ZnO. The turn-on field required to draw a field emission (FE) current density at 1μA/cm2 is found to be 2.5, 2.3, 1.8 and 1.7 V/μm for ZnO(Ni0%), ZnO(Ni5%), ZnO(Ni7.5%) and ZnO(Ni10%), respectively.

cond-mat.mtrl-sci↗

arXiv2017

Controlling of ZnO nanostructures morphology for guiding the structural and optical properties

Most of the applications of the nano structures dependent on the morphology which affects the opto electronics properties. This research article provides a pathway of guiding optical properties like band-gap and fluorescence properties by controlled growth of nano-rods, -flowers, -needles or- tubes without external chemical doping, by simple hydro thermal method by controlling over synthesis parameter, temperature.

cond-mat.mtrl-sci↗

arXiv2017

Enhancement of Two photon absorption with Ni doping in the dilute magnetic Semiconductor ZnO Crystalline Nanorods

In this letter, we have investigated the third-order optical nonlinearities of high-quality Ni doped ZnO nanorods crystallized in wurtzite lattice, prepared by the wet chemical method. In our experiments, we found that the two photon absorption coefficient beta increases by as much as 14 times i.e. 7.6 err 0.4 to 112 err 6 cm per GW, when the Ni doping is increased from 0 to 10 percent. The substantial enhancement in beta is discussed in terms of the bandgap scaling and Ni doping. Furthermore, we also show that the optical bandgap measured by UVVis and photo luminescence spectroscopic, continuously red shift with increasing Ni doping concentration. We envision that the strong nonlinear optical properties together with their dilute magnetic effects, they form an important class of materials for potential applications in magneto-optical and integrated optical chips.

cond-mat.mtrl-sci↗

arXiv2017

Controlling of ZnO nanostructures by solute concentrationand its effect on growth, structural and optical properties

ZnO nanostructured films were prepared by chemical bath deposition method on glass substrates without any assistance of either microwave or high pressure autoclaves. The effect of solute concentration on the pure wurtzite ZnO nanostructure morphologies is studied. The controlling of the solute concentration help to control nano-structure in the form of nano-needles, and rods.

cond-mat.mtrl-sci↗

arXiv2017

Structural and ferroelectric properties of perovskite Pb(1-x)(K0.5Sm0.5)xTiO3 ceramics

PbTiO3 has the highest tetragonal distortion (c/a=1.064) and highest spontaneous polarization among perovskite titanates. But, it is hazardous and hence one needs to reduce Pb content by substituting or reducing Pb content for use in applications. Pb(1-x)(K0.5Sm0.5)xTiO3 (0&x&0.5) perovskite powders were synthesized by sol-gel process, where Pb2+ was replaced by a combination of K+10.5Sm+30.5 (equivalent charge and comparable ionic radius) providing an excellent substitution model to study changes in structural and electrical properties. Vibrational properties and dielectric properties are modified with substitution. A polar tetragonal to a nearly nonpolar cubic phase transition decreases to lower temperatures with substitution due to reduces the lattice strain with substitution. Ferroelectricity is retained even for x=0.5, which has a nearly cubic phase and makes the material technologically important.

cond-mat.mtrl-sci↗

arXiv2017

Structural and dielectric properties of Pb(1-x)(Na0.5Sm0.5)xTiO3 ceramics

A correlation between structure and vibrational properties related to a ferroelectric to paraelectric phase transition in perovskite Pb(1-x)(Na0.5Sm0.5)xTiO3 (PNST - x) polycrystalline powders is discussed. Substitution leads to reduction of tetragonality which is associated with a shift of the phase transition to lower temperatures. The nature of the phase transition gets diffused with increasing substitution.

cond-mat.mtrl-sci↗

arXiv2016

Importance of strain reduction in improvement of optical transmission and conductance in Si4+ doped ZnO: a probable new moisture resistant Transparent Conductive Oxide

Si doped ZnO has been reported to be a better conductor than pure ZnO. It is reported that carrier density increases and hence conductivity increases. However, the effect on optical transmission is yet not clear until our recent report [1]. Zn1-xSixO for x= 0, 0.013, 0.020 and 0.027 have been synthesized using sol-gel method (a citric acid-glycerol route) followed by solid state sintering. We found that there is a decrease in defect states due to Si doping. The correlation of strain to the decrement in vacancy sites is discussed in this report. In modern electronics and solar cell fabrication, transparent conductive oxides (TCOs) are important components which conduct electrically without absorbing visible light. Known TCOs are extremely costly and are composed of non-abundant elements. Search for new ecofriendly, cheap and sustainable TCOs has been a recent research of attraction. Keeping in mind that most solar cells are exposed to natural conditions, the humidity tolerance becomes a determining factor. We report that sensitivity to moisture decreases drastically while the conductivity and optical transparency increases with doping. The reduction of strain and improvement of transport properties results in increased conductivity of Si doped ZnO pellets, tempting us to envisage this material as a probable alternate TCO.

cond-mat.mtrl-sci↗

arXiv2012

High-Tc superconductivity and antiferromagnetism in multilayer cuprates: 63Cu- and 19F-NMR on five-layer Ba2Ca4Cu5O10(F,O)2

We report systematic Cu- and F-NMR measurements of five-layered high-Tc cuprates Ba2Ca4Cu5O10(F,O)2. It is revealed that antiferromagnetism (AFM) uniformly coexists with superconductivity (SC) in underdoped regions, and that the critical hole density pc for AFM is ~ 0.11 in the five-layered compound. We present the layer-number dependence of AFM and SC phase diagrams in hole-doped cuprates, where pc for n-layered compounds, pc(n), increases from pc(1) ~ 0.02 in LSCO or pc(2) ~ 0.05 in YBCO to pc(5) ~ 0.11. The variation of pc(n) is attributed to interlayer magnetic coupling, which becomes stronger with increasing n. In addition, we focus on the ground-state phase diagram of CuO2 planes, where AFM metallic states in slightly doped Mott insulators change into the uniformly mixed phase of AFM and SC and into simple d-wave SC states. The maximum Tc exists just outside the quantum critical hole density, at which AFM moments on a CuO2 plane collapse at the ground state, indicating an intimate relationship between AFM and SC. These characteristics of the ground state are accounted for by the Mott physics based on the t-J model; the attractive interaction of high-Tc SC, which raises Tc as high as 160 K, is an in-plane superexchange interaction Jin (~ 0.12 eV), and the large Jin binds electrons of opposite spins between neighboring sites. It is the Coulomb repulsive interaction U ~ (> 6 eV) between Cu-3d electrons that plays a central role in the physics behind high-Tc phenomena.

cond-mat.supr-con↗

arXiv2011

Antiferromagnetism, superconductivity, and pseudogap in three-layered high-T_c cuprates Ba_2Ca_2Cu_3O_6(F,O)_2 probed by Cu-NMR

We report on the phase diagram of antiferromagnetism (AFM) and superconductivity (SC) in three-layered Ba_2Ca_2Cu_3O_6(F,O)_2 by means of Cu-NMR measurements. It is demonstrated that AFM and SC uniformly coexist in three-layered compounds as well as in four- and five-layered ones. The critical hole density p_c for the long range AFM order is determined as p_c ~ 0.075, which is larger than p_c ~ 0.02 and 0.055 in single- and bi-layered compounds, and smaller than p_c ~ 0.08-0.09 and 0.10-0.11 in four- and five-layered compounds, respectively. This variation of p_c is attributed to the magnetic interlayer coupling which becomes stronger as the stacking number of CuO_2 layers increases; that is, the uniform coexistence of AFM and SC is a universal phenomenon in underdoped regions when a magnetic interlayer coupling is strong enough to stabilize an AFM ordering. In addition, we highlight an unusual pseudogap behavior in three-layered compounds -- the gap behavior in low-energy magnetic excitations collapses in an underdoped region where the ground state is the AFM-SC mixed phase.

cond-mat.supr-con↗

arXiv2011

Reply to "Comment on 'Isotope effect in multi-band and multi-channel attractive systems and inverse isotope effect in iron-based superconductors'"

The Comment insists on the following: in our model it is assumed that the effective interactions have specific energy ranges within the single band with a cutoff at ω_1 for the phononic part and a range from ω_1 to ω_2 in the AF channel. Our reply is that we assume that V_i(k,k')\neq 0 if |ξ_k|<ω_i and |ξ_{k'}|<ω_i, and otherwise V_i(k,k')= 0 (i=1,2), as stated in our paper. This is the model of BCS type with two attractive interactions, and this assumption is the characteristic of the BCS approximation. The claim "the integration limits have been modified such that the AF channel mediated pairing sets in where the ph-channel pairing terminates and is limited at an energy given by ω_j=ω_{AF}" in the Comment is wrong. We describe the model and the method to solve the gap equation in more detail.

cond-mat.supr-con↗

arXiv2011

Planar CuO_2 hole density estimation in multilayered high-T_c cuprates

We report that planar CuO_2 hole densities in high-T_c cuprates are consistently determined by the Cu-NMR Knight shift. In single- and bi-layered cuprates, it is demonstrated that the spin part of the Knight shift K_s(300 K) at room temperature monotonically increases with the hole density $p$ from underdoped to overdoped regions, suggesting that the relationship of K_s(300 K) vs. p is a reliable measure to determine p. The validity of this K_s(300 K)-p relationship is confirmed by the investigation of the p-dependencies of hyperfine magnetic fields and of spin susceptibility for single- and bi-layered cuprates with tetragonal symmetry. Moreover, the analyses are compared with the NMR data on three-layered Ba_2Ca_2Cu_3O_6(F,O)_2, HgBa_2Ca_2Cu_3O_{8+delta}, and five-layered HgBa_2Ca_4Cu_5O_{12+delta}, which suggests the general applicability of the K_s(300 K)-p relationship to multilayered compounds with more than three CuO_2 planes. We remark that the measurement of K_s(300 K) enables us to separately estimate p for each CuO_2 plane in multilayered compounds, where doped hole carriers are inequivalent between outer CuO_2 planes and inner CuO_2 planes.

cond-mat.supr-con↗

arXiv2011

Novel Superconducting Phases in Copper Oxides and Iron-oxypnictides: NMR Studies

We reexamine the novel phase diagrams of antiferromagnetism (AFM) and high-Tc$ superconductivity (HTSC) for a disorder-free CuO$_2$ plane based on an evaluation of local hole density ($p$) by site-selective Cu-NMR studies on multilayered copper oxides. Multilayered systems provide us with the opportunity to research the characteristics of the disorder-free CuO$_2$ plane. The site-selective NMR is the best and the only tool used to extract layer-dependent characteristics. Consequently, we have concluded that the uniform mixing of AFM and SC is a general property inherent to a single CuO$_2$ plane in an underdoped regime of HTSC. The $T$=0 phase diagram of AFM constructed here is in quantitative agreement with the theories in a strong correlation regime which is unchanged even with mobile holes. This {\it Mott physics} plays a vital role for mediating the Cooper pairs to make $T_c$ of HTSC very high. By contrast, we address from extensive NMR studies on electron-doped iron-oxypnictides La1111 compounds that the increase in $T_c$ is not due to the development of AFM spin fluctuations, but because the structural parameters, such as the bond angle $α$ of the FeAs$_4$ tetrahedron and the a-axis length, approach each optimum value. Based on these results, we propose that a stronger correlation in HTSC than in FeAs-based superconductors may make $T_c$ higher significantly.

cond-mat.supr-con↗

arXiv2010

Synthesis of ErFeAsO-based superconductors by hydrogen doping method

Here we demonstrate the technique to stabilize the ErFeAsO-based superconductor with the smallest lattice constants in LnFeAsO1-y (Ln = lanthanide) series using hydrogen doping method. Polycrystalline samples were synthesized by heating pellets with nominal compositions of ErFeAsO1-y (1-y = 0.75 ~ 0.95) sandwiched between pellets of LaFeAsO0.8H0.8 compositions at 1100 °C under a pressure of 5.0 - 5.5 GP. The sample with lattice constants of a = 3.8219 Å and c = 8.2807 Å shows the highest superconducting critical temperatures (Tc) of 44.5 K and 41.0 K determined by onset transitions of resistivity and susceptibility, respectively. We discuss phase diagram of Ln dependence of Tc in LnFeAsO-based superconductors.

cond-mat.supr-con↗

arXiv2010

Superconductivity at 28.3 and 17.1 K in (Ca4Al2O6-y)(Fe2Pn2) (Pn = As and P)

We have successfully synthesized (Ca4Al2O6-y)(Fe2Pn2) (Pn = As and P) (Al-42622(Pn)) using high-pressure synthesis technique. Al-42622(Pn) exhibit superconductivity for both Pn = As and P with the transition temperatures of 28.3 K and 17.1 K, respectively. The a-lattice parameters of Al-42622(Pn) (a = 3.713 Å and 3.692 Å for Pn = As and P, respectively) are smallest among the iron-pnictide superconductors. Correspondingly, Al-42622(As) has the smallest As-Fe-As bond angle (102.1 °) and the largest As distance from the Fe planes (1.500 Å).

cond-mat.supr-con↗

arXiv2010

Absence of an appreciable iron isotope effect on the transition temperature of the optimally doped SmFeAsO_{1-y} superconductor

We report the iron (Fe) isotope effect on the transition temperature (Tc) in the oxygen-deficient SmFeAsO_{1-y}, a 50 K-class Fe-based superconductor. For the optimally-doped samples with Tc = 54 K, change of the Fe average atomic mass (MFe) causes a negligibly small shift in Tc, with the Fe isotope coefficient (alphaFe) as small as -0.024 \pm 0.015. This result contrasts with the finite, inverse isotope shift observed in optimally-doped (Ba,K)Fe2As2, indicating that the contribution of the electron-phonon interaction markedly differs between these two Fe-based high-Tc superconductors.

cond-mat.supr-con↗