Reduction In Lattice Parameter Research Articles

The effect of Cu addition on the morphological, structural and mechanical characteristics of nanocrystalline NiTi shape memory alloys

An attempt has been made to develop the nanostructured NiTi and NiTiCu shape memory alloys (SMAs) using mechanical milling method. The effects of milling and the addition of Cu as ternary element in NiTi SMA was analysed by evaluating its structural and morphological characteristics. Experimental results obtained from the XRD phase analysis, crystalline nature, crystallite size and lattice strain of the synthesized monocrystalline elements, confirmed the formation of B2 phase-intermetallics such as NiTiCu and NiTi. The microstructural characteristics and formation of agglomerates in case of NiTi and NiTiCu system can be altered by increasing the milling time. The results suggest that the use of mechanical synthesis for NiTi based shape memory alloys stimulates the formation of solid phase homogeneous nanocrystalline elements. Addition of Cu in NiTi resulted in the formation of nanocrystalline with a size of ∼23 nm. The diffraction patterns of nanocrystalline NiTi SMAs were characterized with diffraction rings and reduction in lattice parameter.

SYNTHESIS OF COMPOSITE POWDERS «TIC – NICRBSI ALLOY BINDER» FOR CLADDING AND DEPOSITION OF WEAR-RESISTANT COATINGS

TiC + NiCrBSi binder metal matrix composites were obtained by self-propagating high-temperature synthesis (SHS) in the reaction powder mixtures of titanium, carbon (carbon black) and NiCrBSi alloy. It has been found that steady combustion in a stationary mode occurs when the content of the thermally inert metal binder in reactive mixtures does not exceed 50 vol.%. Porous SHS cakes were crashed and resulting granules were separated to fractions by screening to get the composite powder fraction necessary for coating application. Synthesis products were studied by optical and scanning electron microscopy, X-ray diffraction and electron microprobe analysis. It has been found that the average size of carbide inclusions depends on the content of thermally inert alloy powder in the reaction mixtures and can be purposefully regulated in a wide range. The microhardness of composite powder granules obtained by crushing the SHS conglomerates decreases monotonically with an increasing content of the metal binder having hardness less than that of titanium carbide. According to X-ray diffraction data, the titanium carbide lattice parameter turns out to be considerably less than values known for equiatomic titanium carbide. It has been found by electron microprobe analysis of carbide inclusions in the composite structure that the ratio of carbon and titanium mass contents is 0,21 as compared with 0,25 in equiatomic titanium carbide. Iron and silicon contents in the carbide are negligible, oxygen and nickel contents are below 1 wt.%, and chromium content is 2,5 wt.%. The analysis of known data on the effect of all the above-listed dopants on the titanium carbide lattice allows for a conclusion that the carbon deficit is a main reason of the lattice parameter reduction.

Effect of chitosan coating on the structural and magnetic properties of MnFe2O4 and Mn0.5Co0.5Fe2O4 nanoparticles

We report the influence of polymer coatings on structural and magnetic properties of MnFe2O4 and Mn0.5Co0.5Fe2O4 nanoferrites synthesized by glycol thermal technique and then coated with chitosan viz. CHI-MnFe2O4 and CHI-Mn0.5Co0.5Fe2O4. The compounds were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), high-resolution scanning electron microscopy (HRSEM), Mössbauer spectroscopy and magnetization measurements. The powder XRD patterns of naked nanoferrites confirmed single-phase spinel cubic structure with an average crystallite size of 13 nm, while the coated samples exhibited an average particle size of 15 nm. We observed a reduction in lattice parameters with coating. HRTEM results correlated well with XRD results. 57Fe Mössbauer spectra showed ordered magnetic spin states in both nanoferrites. This study shows that coatings have significant effects on the structural and magnetic properties of Mn-nanoferrites. Magnetization studies performed at room temperature in fields up to 14 kOe revealed the superparamagnetic nature of both naked and coated nanoparticles with spontaneous magnetizations at room temperature of 49.2 emu/g for MnFe2O4, 23.6 emu/g for coated CHI–MnFe2O4 nanoparticles, 63.2 emu/g for Mn0.5Co0.5Fe2O4 and 33.2 emu/g for coated CHI–Mn0.5Co0.5Fe2O4 nanoparticles. We observed reduction in coercive fields due to coating. Overall, chitosan-coated manganese and manganese-cobalt nanoferrites present as suitable candidates for biomedical applications owing to physicochemical, and magnetic properties exhibited.

The effect of milling time on structural, optical and photoluminescence properties of ZnO nanocrystals

The crystallite size of commercial ZnO nanocrystals was tuned from 22.5 to 13.8nm by ball-milling technique. X-ray diffraction patterns of mechanically milled ZnO nanocrystals reveal that milled samples possess the wurtzite-type hexagonal structure of ZnO. Increasing milling time results in the decrease of crystallite size and reduction of lattice parameters due to a slight increase of internal compressive strain and dislocation density. Scanning electron microscope images demonstrate the appearance of large agglomerated particles with ambiguous edges due to large aggregation tendency with slight variation in the particle size at milling time 8h. Analysis of the optical absorption spectra at different milling time indicates the blue shift of exciton absorption peak and optical gap photoluminescence spectra reveal that mechanical milling of ZnO NCs leads to quenching of emission intensity due to the creation of nonradiative centers via increasing thermal strain and mechanical deformation produced during the milling process.

Crystal Structure and Bonding Analysis of (La0.8Ca0.2)(Cr0.9−x Co0.1Cu x )O3 Ceramics

Abstract In this article, structural properties and bonding behaviours of codoped lanthanum chromites (La0.8Ca0.2)(Cr0.9−x Co0.1Cu x )O3 (x=0.00, 0.03, and 0.12) were investigated in detail. Polycrystalline chromite samples (La0.8Ca0.2)(Cr0.9−x Co0.1Cu x )O3 (x=0.00, 0.03, and 0.12) were prepared by a standard solid-state reaction process. The synthesised samples were characterised for their structural, morphological, optical, and magnetic properties using powder XRD, SEM/EDS, UV–Vis, and VSM. XRD data showed that the samples were crystallised into a single phase with orthorhombic structure. Powder profile refinement analysis suggested the reduction in lattice parameters and cell volume with the addition of Cu. The electron density distributions and the bonding features of the prepared samples have been investigated using maximum entropy method (MEM). The mid bond electron density values revealed the enhancement of ionic nature between lanthanum and oxygen ions and a reduction in covalent nature between chromium and oxygen ions. Heterogeneous distribution of particles with different sizes was observed through SEM micrographs. EDS spectra confirms the presence of constituent elements in the prepared samples. Optical band gap values are decreasing with the addition of Cu. Antiferromagnetic ordering was observed from M–H curves obtained at room temperature. The structural and the magnetic properties are correlated.

Piezoelectric softening by Nb substitution in (Ba,Pb)ZrO3 ceramics

AbstractDonor doping is commonly applied for softening of the piezoelectric and dielectric properties and facilitation of polarization switching in the ubiquitous Pb(Zr,Ti)O3 [PZT] ceramics. The origin of the donor‐dopant effects is not entirely clear. (Pb,Ba)ZrO3 [PBZ] is a related ferroelectric material, its perovskite A‐site being partially occupied by the larger Ba+2 cation, less prone to evaporation than Pb+2, and the B‐site is occupied entirely by the valency‐stable Zr+4. Here we report on our studies of Nb+5 doping effects in (Pb,Ba)ZrO3. Similarly, to past observations on La+3 and Nb+5 doped PZT, we find a strong reduction in relative density of PBZ when the doping is <0.5 atomic %. This is accompanied by lattice parameter reduction, enhanced PbO loss, smaller grain size and deterioration of dielectric, piezoelectric and polarization switching properties, the latter being opposite of expected softening effect. All those observations can be interpreted in terms of the Nb entering A‐site at small concentrations. This is supported by ab‐inito calculations and analysis of the possible defect reaction equations. The structure and microstructure of PBZ with Nb>0.2% are consistent with Nb+5 entering the B‐site and softening effects are observed. The study supports the scenario of hardening due to domain walls pinning by VPb‐VO divacancies and softening upon decrease in their concentration.

Evidence of Magnetoelectric coupling in Bi2(1-x)Ho2xFe4O9 (x=0, 0.01) multiferroic ceramics

We report structural, magnetic, dielectric and magnetoelectric properties of orthorhombic Bi2(1-x)Ho2xFe4O9 (x=0, 0.01) ceramics (space group ‘Pbam’) synthesized by conventional solid state reaction route. Rietveld refined X-ray diffraction (XRD) shows phase formation of the samples along with reduction in lattice parameters and cell volume due to lower ionic radii substitution of Ho3+ at Bi3+-site. DC magnetization study revealed antiferromagnetic transition (TN) of the parent (BFO = 250 K) as well as 1% Ho substituted sample (BHFO1 = 253 K) along with increase in magnetization. Opening of hysteresis was observed for BHFO1 sample implying onset of weak ferromagnetism with dominating antiferromagnetic behaviour. Moreover, temperature dependent dielectric (ε') study and its derivative (dε'/dT) for both the samples show significant anomaly around the antiferromagnetic transition (TN) thus, implying a plausible magnetoelectric coupling between the magnetic as well as the electric order parameters in the studied samples. Magnetoelectric coupling was also confirmed from temperature and magnetic field (1.3 T) dependant tan loss plots.

Two-dimensional GeP3 as a high capacity electrode material for Li-ion batteries.

Two-dimensional (2D) materials are promising for use in lithium (Li) electrodes due to their high surface ratio. By using density functional theory (DFT) calculations, we investigate the adsorption and diffusion of Li on a newly predicted 2D GeP3 material [Nano Lett., 2016, 17, 1833]. The most favourable adsorption sites for Li are identified, and a semiconducting to metallic transition induced by Li adsorption is found, which indicates excellent electrical conductivity. The GeP3 monolayer has an estimated capacity of 648 mA h g-1, which is almost twice that of commercially used graphite (375 mA h g-1). During full Li intercalation, the GeP3 layer undergoes only 1.2% lattice parameter reduction. Moreover, GeP3 possesses the advantages of a small diffusion barrier (∼0.5 eV) and low average open-circuit voltages (∼0.4 V). Our results highlight a new class of promising anode materials, i.e. 2D phosphide, as potential rechargeable lithium batteries with ultrahigh-capacity, superior ionic conductivity, and low average open-circuit voltage.

Thermoelectric properties of Sn doped BiCuSeO

BiCuSeO and Bi1-xSnxCuSeO (x=0.02, 0.04, 0.06, 0.08) were prepared by a two-step solid state synthesis. The phase purity and the crystal structure were investigated by the X-Ray Diffraction (XRD) and confirmed by Energy Dispersive Spectroscopy (EDS). The volatilization of Bi and Bi2O3 lead to off-stoichiometry of the main phase and the formation of CuSe2 secondary phase in the undoped sample. SnO2 secondary phases were found in the doped samples. Both the Seebeck coefficient and the electrical resistivity, measured from the room temperature to 773K linearly increases with the temperature, which indicates that the sample have metallic like behavior. The origin of such a behavior is due to high hole concentration originating from the Bi and the O vacancies. The Sn +4 valence state was confirmed from the X-Ray Photoelectron Spectroscopy (XPS) and from the reduction of lattice parameter ‘a’ with doping. The substitution of Sn+4 in the place of Bi+3 leads to the higher Seebeck coefficient and electrical resistivity in the doped samples. Highest power-factor (∼1mW/m-K2 at 773K), was obtained for the undoped sample and the 4% Sn doped sample (Bi0.96Sn0.04CuSeO). The lowest thermal conductivity was obtained for the undoped sample, from the room temperature to 773K. The presence of thermally-conducting SnO2 secondary phases in the doped samples increases the thermal conductivity in comparison with the undoped sample. The zTs of the doped samples were lower compared to the undoped sample, owing to their higher thermal conductivity. The oxygen vacancies as well as the all-length scale phonon scattering, lowers the thermal conductivity of the undoped sample and, as a result, a maximum zT of 1.09 was achieved at 773K.

Effect of La2O3 addition on the microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 ceramics

In this paper, Ba(Mg1/3Ta2/3)O3 (BMT) ceramics with x (x = 0–5) wt% La2O3 were prepared by the conventional solid-state ceramic route for investigating the effect of La2O3 addition on the microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 ceramics. The XRD results showed that the main crystal phase in the sintered ceramics was Ba(Mg1/3Ta2/3)O3 and the secondary phase Ba0.5TaO3 was presented depending on the La2O3 contents. SEM photographs suggested that La2O3 working as sintering additives promoted the densification and grain growth. Proper La3+ substituted for Ba2+ site in Ba(Mg1/3Ta2/3)O3, which led to the reduction of lattice parameters of Ba(Mg1/3Ta2/3)O3. And the result had positive effect on the dielectric properties, especially the Q × f value. As increasing La2O3 content from 0 to 5 wt%, the dielectric constant (er) increased from 24.9 to 26.3, and the Q × f value increased first from 58,000 GHz to the peak value of 112,000 GHz (4 wt% La2O3) and thereafter decreased to 68,000 GHz. Meanwhile the temperature coefficient of resonant frequency (τf) decreased first to a minimum value and increased thereafter. At last, Ba(Mg1/3Ta2/3)O3 ceramics with 4 wt% La2O3 sintered at 1400 °C for 5 h had compact and homogeneous microstructure and possessed excellent microwave dielectric properties: high dielectric constant er = 25.9, high Q × f = 112,000 GHz, and near-zero τf = +0.3 ppm/°C.

Controlled and enhanced dielectric properties of high-titanium containing LixTi0.1Ni1⿿xO via chemical composition-tailoring

Tuning the dielectric properties via composition-tailoring is demonstrated for variable-lithium, constant-titanium co-doped nickel oxide (LixTi0.1Ni1⿿xO; x=0.05⿿0.30; referred to LTNO). The effect of variable Li-content on the structure and dielectric properties of LTNO is investigated. X-ray diffraction studies confirm the formation of a cubic NiO phase in LTNO for x=0.05⿿0.30. However, lattice parameter reduction was evident with increasing Li-content. Composition-driven giant dielectric constant (104⿿105) was observed for a higher lithium content (x=0.15⿿0.30) leading to realization of LTNO ceramics. The origin of the high dielectric constant observed in these low density LTNO ceramics is attributed to the Maxwell⿿Wagner polarization mechanism.

Site location of Al-dopant in ZnO lattice by exploiting the structural and optical characterisation of ZnO:Al thin films

The zinc oxide thin films, highly transparent, doped aluminium were prepared on glass substrates by the reactive chemical spray method. The incorporation nature of Al atoms in the ZnO lattice was determined by X-ray diffraction and optical analyses. Indeed, for low doping ⩽2%, the results of X-ray spectra analysis show a simultaneous reduction of lattice parameters (a and c), this variation, which follows VEGARD’s law, tends to indicate a substitution of Zn by Al. By against for doping >2% the increase in the lattice parameters thus the grain sizes, in accordance with the VEGARD’s law can be explained by occupation of the interstitial sites by Al atoms. Beyond 4%, the material tends to get disorderly and the crystallites orientation is random. The studied optical properties show that the variation of the optical gap follows a law of the x3/2 form for x<3% (x is the aluminium atom fraction incorporated in the ZnO lattice). The granular structure is fairly visible and some local growths are disrupted. The crystallite size at low enlargement is coherent with the XRD results.

Ultrasound Assisted Synthesis and Characterization of Mn Doped CdS Nanocrystalline Zinc-Blendes

Cd1-xMnxS (x = 0, 0.1, 0.2) nanoparticles, prepared by co-precipitation method under ultrasonic irradiation, were studied by means of X-ray diffraction, scanning electron microscopy, FTIR and UV-Vis spectroscopy measurements. The average particle size of nanoparticles from the scanning electron microscopy image is about 20-30 nm. Results show that partial substitution of Cd by Mn leads to a reduction in lattice parameters and enhancement of band gap energy. This is attributed to the nanometric grain size and quantum confinement effects. The particle size is calculated to be around 2 nm that is almost in agreement with the crystallite size estimated from the XRD result.

Synthesis, characterization, in vitro bioactivity and antimicrobial activity of magnesium and nickel doped silicate hydroxyapatite

Incorporation of Mg2+, Ni2+, and SiO44− ions into hydroxyapatite (HA) structure was successfully carried out by microwave assisted wet precipitation method to furnish Ca10−x−yMgxNiy(PO4)6−z(SiO4)z(OH)2−z□z. Incorporation of silicate ions into the HA structure led to the increase in HA lattice parameters, while incorporation of (Mg2+ and Ni2+) ions led to the reduction of lattice parameters and crystallite size of silicate doped HA. Optical analysis showed a distinct red-shift upon increase in Ni2+ concentration. Dissolution of samples in simulated body fluid showed that the incorporation of Mg2+, Ni2+ and SiO44− in HA structure resulted in considerable increase in the in vitro dissolution of HA. The prepared samples promoted exceptional in vitro apatite growth over 14 days with Ca/P ratio close to 1.67. The analysis of in vitro antibacterial activity against E. coli and P. aeruginosa revealed that the Ni2+ containing samples possessed good antibacterial properties.

Effect of Zn2+ ions on the structure, morphology and optical properties of CaWO4 microcrystals

The effect of zinc ions (Zn2+) on the structure, morphology and optical properties of (Ca1−x Zn x )WO4 microcrystals with (x = 0, 0.01, 0.02, and 0.03) obtained by the microwave-hydrothermal method at 170 °C for 1 h is reported in this letter. These microcrystals were characterized by X-ray diffraction (XRD), Rietveld refinement, energy dispersive X-rays spectroscopy (EDXS) and field emission scanning electron microscopy (FE-SEM) images. The optical properties were investigated by ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy and photoluminescence (PL) measurements. XRD patterns and Rietveld refinement data indicated that all the (Ca1−x Zn x )WO4 microcrystals present a tetragonal structure and a reduction of lattice parameters and unit cell volume occurs with the increase of Zn2+. EDXS data confirms that the elemental chemical composition was achieved for (Ca1−x Zn x )WO4 microcrystals. FE-SEM images showed that the replacement of Ca2+ by the Zn2+ promotes a reduction of average crystals size and considerable changes in crystal shape starting from dumbbell-like to decorative ball-like (Ca1−x Zn x )WO4 microcrystals. UV–Vis spectra evidenced a small increase in optical band gap values (from 5.72 to 5.76 eV). Finally, PL emission of (Ca1−x Zn x )WO4 microcrystals was improved until x = 0.02 due to the presence of defects at medium range and new intermediate electronic levels in the band gap associated to the Zn2+ content.

Effect of Mn doping on structural, dielectric and magnetic properties of BiFeO3 thin films

Bismuth iron oxide is amongst the class of materials that exhibit simultaneous presence of ferromagnetic and ferroelectric properties with potential applications in spintronic devices. However, there are some problems associated with BiFeO3 including large leakage current, volatile nature of Bi2O3 along with weak ferromagnetic/antiferromagnetic behavior. In order to overcome these difficulties we here report the effect of manganese (Mn) doping on BiFeO3 (BiFe1−xMnxO3 where x = 0.0–0.3, with interval of 0.05) thin films prepared using sol–gel and spin coating method. X-ray diffractometer (XRD) results show formation of phase pure rhombohedrally distorted perovskite structure. However, with the increase in Mn content, XRD peak positions shift to higher angle indicating reduction in lattice parameters and consequently the unit cell volume. Crystallite size in un-doped and Mn-doped BiFeO3 films is below cycloidal spin arrangement of BiFeO3, i.e. 62 nm. This along with charge compensation mechanism, arising due to replacement of trivalent cation with divalent ion, enhances the magnetic properties of BiFe1−xMnxO3 thin films. Ferromagnetic behavior instead of antiferromagnetic nature of BiFeO3 is observed in these BiFe1−xMnxO3 thin films for all Mn concentrations. High saturation magnetization of 102 emu/cm3 was observed for Mn content of 0.2. Dielectric constant increases and the dielectric loss decreases as the dopant concentration is increased resulting in high dielectric constant and low dielectric loss at x = 0.25. The surface work function (wf) has been calculated using Scanning Kelvin Probe technique. The wf results are correlated to the structural and then dielectric properties.

Chemical delithiation and exfoliation of [formula omitted

Progressive chemical .delithiation of commercially available lithium cobalt oxide (LiCoO2) showed consecutive changes in the crystal properties. Rietveld refinement of high resolution X-ray and neutron diffraction revealed an increased lattice parameter c and a reduced lattice parameter a for chemically delithiated samples. Using electron microscopy we have also followed the changes in the texture of the samples towards what we have found is a critical layer stoichiometry of about LixCoO2 with x=1/3 that causes the grains to exfoliate. The pattern of etches by delithiation suggests that unrelieved strain fields may produce chemical activity.

In situ examination of oxygen non-stoichiometry in La0.80Sr0.20CoO3−δ thin films at intermediate and low temperatures by x-ray diffraction

Structural evolution of epitaxial La0.80Sr0.20CoO3−δ thin films under chemical and voltage stimuli was examined in situ using X-ray diffraction. The changes in lattice parameter (chemical expansivity) were used to quantify oxygen reduction reaction processes and vacancy concentration changes in lanthanum strontium cobaltite. At 550 °C, the observed lattice parameter reduction at an applied bias of −0.6 V was equivalent to that from the reducing condition of a 2% carbon monoxide atmosphere with an oxygen non-stoichiometry δ of 0.24. At lower temperatures (200 °C), the application of bias reduced the sample much more effectively than a carbon monoxide atmosphere and induced an oxygen non-stoichiometry δ of 0.47. Despite these large changes in oxygen concentration, the epitaxial thin film was completely re-oxidized and no signs of crystallinity loss or film amorphization were observed. This work demonstrates that the effects of oxygen evolution and reduction can be examined with applied bias at low temperatures, extending the ability to probe these processes with in-situ analytical techniques.

Effect of Dy substitution on structural, magnetic and optical properties of BiFeO3 ceramics

Bi1−xDyxFeO3 (x=0.0, 0.03, 0.05, 0.07, 0.10 and 0.12) ceramics were synthesized by solid state reaction method. Effects of Dy substitution on structural distortion, magnetic and optical properties of BiFeO3 were examined by X-ray diffraction, Raman and UV–Visible spectroscopy. The samples were found to crystallize in rhombohedral structure of BiFeO3 with R3c space group. The reduction in lattice parameters and unit cell volume indicate the distortion in FeO6 octahedra of the rhombohedral structure without any signature of phase transformation up to x=0.12. The predictable weak ferromagnetic hysteresis loops can be observed in the Dy doped samples with maximum remnant magnetization of 0.2103emu/g for x=0.12. The weak ferromagnetism is ascribed to the suppressed spiral spin structure and magnetically active characteristic of Dy3+ ions together with ferromagnetic coupling between Dy3+ and Fe3+ ions. With optical band gap in visible region, Dy doped BiFeO3 ceramics are potential material for optoelectronic device and solar cell applications.

Ferroelectric and structural instability of (Pb,Ca)TiO3 thin films prepared in an oxygen atmosphere and deposited on LSCO thin films which act as a buffer layer

Structural, microstructural and ferroelectric properties of Pb0.90Ca0.10TiO3 (PCT10) thin films deposited using La0.50Sr0.50CoO3 (LSCO) thin films which serve only as a buffer layer were compared with properties of the thin films grown using a platinum-coated silicon substrate. LSCO and PCT10 thin films were grown using the chemical solution deposition method and heat-treated in an oxygen atmosphere at 700°C and 650°C in a tube oven, respectively. X-ray diffraction (XRD) and Raman spectroscopy results showed that PCT10 thin films deposited directly on a platinum-coated silicon substrate exhibit a strong tetragonal character while thin films with the LSCO buffer layer displayed a smaller tetragonal character. Surface morphology observations by atomic force microscopy (AFM) revealed that PCT10 thin films with a LSCO buffer layer had a smoother surface and smaller grain size compared with thin films grown on a platinum-coated silicon substrate. Additionally, the capacitance versus voltage curves and hysteresis loop measurement indicated that the degree of polarization decreased for PCT10 thin films on a LSCO buffer layer compared with PCT10 thin films deposited directly on a platinum-coated silicon substrate. This phenomenon can be described as the smaller shift off-center of Ti atoms along the c-direction 〈001〉 inside the TiO6 octahedron unit due to the reduction of lattice parameters. Remnant polarization (Pr) values are about 30μC/cm2 and 12μC/cm2 for PCT10/Pt and PCT10/LSCO thin films, respectively. Results showed that the LSCO buffer layer strongly influenced the structural, microstructural and ferroelectric properties of PCT10 thin films.