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Polycrystalline samples of (Ba1−xLax)(Ti0.85−xCoxSn0.15)O3 (x = 0.00, 0.01, 0.03 and 0.05) with equivalent substitution of La3+ at the place of Ba2+ and Co3+ at the place of Ti4+ were synthesized by the conventional solid-state ceramic route. The prepared samples were characterized by the X-ray diffraction technique for crystal structure. Samples with x ≤ 0.03 were found to have cubic structure at room temperature. Almost no change is found in the lattice parameters due to simultaneous doping of La and Co at A and B sites, respectively. Scanning electron micrographs showed that the grain size was in the range of 2–4 μm. A broad peak in dielectric permittivity vs. temperature plot was observed, indicating a diffuse phase transition in these materials. Dielectric measurements depicted an increase in the broadness of the transition peak and its shifting toward lower temperatures with increasing co-doping of La and Co. Samples with x = 0.01 showed high permittivity ~ 4720 at room temperature and very low dielectric loss ~ 0.009 in the temperature range of 280–330 K at 1 kHz. Hysteresis loop measurements done at room temperature indicated a decrease in remanence due to doping.

The kinetics of oxygen reduction reaction (ORR), being a prime requisite for electrode materials after the higher conductivity. Further, electrodes are observed to dissolute on reaction at triple phase boundary. However, the compositional effect on ORR is least understood. In order to inspect the ORR mechanism with substitution, a series of (1 + x) PrCoO3 − (1 − x) BaCoO3 (x = 0.2 to 1.0 with step of 0.2) compositions are prepared using conventional solid-state route method. The Rietveld refinement of X-ray diffractograms and specific heat curves confirms the formation of double phase comprising orthorhombic Pmmm phase corresponding to PrBaCo2O6-δ and Pnma phase corresponding to PrCoO3 for x = 0.2 to 0.8 with well connected and porous microstructure. The triple phase boundary reactions suggest the formation of Co(OH)3 along with H2 gas on reaction of these composite electrodes with H2O during electrochemical dissolution. However, chronoamperometric studies prove the suitability of x = 0.6 sample with higher ORR and liberation of H2 gas at room temperature.

Sodium bismuth titanate samples with different morphology were synthesized via varying the sintering temperature from 1000 to 1150 °C. The conductivity was significantly affected with the morphology of the system. The dynamics of ions was understood from the conductivity spectra. The dc conductivity, hopping frequency and exponent values were extracted from the conductivity spectra analysis. The impedance and modulus spectroscopy along with exponent behaviour suggested short range hopping for the sample sintered at 1000 °C and followed Ghosh scaling instead of Summerfield scaling. While long-range hopping was observed for the samples sintered at 1150 °C and it followed both the Summerfield scaling and Ghosh scaling. Moreover, the stability of the sample is checked in reducing atmosphere.

Rare earth nickelate perovskites have very wide uses, as magnetic insulators, as well as being conducting materials for the various components of solid oxide fuel cells (SOFCs) due to them undergoing an insulator to metal transition below operating temperature. In SOFCs, the microstructural design of electrode materials is an important aspect for electron and oxygen ion conduction at the electrolyte–electrode and electrode–air interfaces. To investigate this feature, a Ruddlesen–Popper structured layered perovskite, (SmSr)NiO4−δ, was synthesized at different sintering temperatures using a solid-state reaction technique. Porous and dense microstructures were obtained at sintering temperatures of 1250 and 1425 °C, respectively. The influence of electrocatalysis on the structures of both surfaces was studied comprehensively. Post cyclic voltammetry structural studies show the presence of Ni–(OH)2 and Ni–OOH species for the samples, respectively, suggesting that they undergo different oxygen reduction reaction mechanisms.

Lotus-like ZnO morphology with reduced graphene oxide was synthesized by sol-gel method using ammonia solution as a reducing agent. It was observed that ammonia solution, reduced graphene oxide (rGO) and working temperature influenced the assembly of inverted and non-inverted lotus like ZnO morphologies with variable sizes in the micrometer range. This type of morphology was successfully developed in the nanosized range and appeared on the surfaces of rGO sheets as well as between their interlayer's. These arrangements influence in enhancing optical and photocatalytic properties. The prepared composites in the above manner also showed better photocatalytic activities for the removal of phenol compound under sunlight irradiation and resulted in maximum degradation efficiency of around 86% in 20 min.

With the global surge in the research on perovskite halides as cost effective alternative Silicon solar cells, it is necessary to find the replacement of very expensive hole transport materials (HTM). Copper oxide (CuO) is one of the inorganic binary compound and much cheaper than the organic HTMs. In this work, light absorption behaviour and photoconductivity of CuO are examined. The band gap and Urbach energy is estimated using UV-visible absorbance spectrum. The photo-conduction study of the CuO is carried in 1.5AM-G solar light.

Lanthanum (La3+)-doped double perovskites Sr2CoMoO6 (Sr2-xLaxCoMoO6, 0.00 ≤ x ≤ 0.03) were synthesized via the citrate-nitrate autocombustion route. The Reitveld refinement analysis of X-ray diffraction reveals the tetragonal symmetry as the main phase with space group I4/m and also confirms the presence of some peaks corresponding to extra phase SrMoO4. The SEM micrograph images reflect that grains are in irregular shape and sizes for all samples. Average grain size gradually decreases with the increase of the SrMoO4 phase. The X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of mixed valence states of Mo5+/Mo6+, Co2+/Co3+, and O-lattice/O-chemisorbed/O-physisorbed species. Coefficient of thermal expansion (CTE) analysis shows that the particular composition Sr1.97La0.03CoMoO6 has the lowest CTE value among the compositions studied. The electrical conductivity of Sr2CoMoO6 is enhanced effectively by doping La at Sr sites. The measured area-specific resistance (ASR) for the composition Sr1.97La0.03CoMoO6 (SLCM03) is found to be appreciably low, ∼0.053 Ohm cm-2 at 800 °C. The obtained highest electrical conductivity with the lowest activation energy and low ASR value for the composition Sr1.97La0.03CoMoO6 encompasses it as a promising candidate for anode material in the intermediate-temperature solid oxide fuel cell (IT-SOFC) application.

The paradigm that chemical synthesis reduces the sintering temperature as compared to solid state synthesis seems to be violated in the case of the PrBaCo2O6-δ double perovskite. The sintering temperatures for pure phase samples synthesized through the solid state route (P-SSR) and the auto-combustion route (P-ACR) were found to be 1050 and 1150 °C, respectively. The porous microstructure of P-SSR is suitable for SOFC cathode materials while that of P-ACR is pore free. High-resolution transmission electron microscopy, Raman and scanning tunneling microscopy studies reveal that there is crystal growth on a smooth surface with a preferred orientation. Our results show that this anomalous synthesis behaviour is due to anisotropic surface nucleation growth. Thermodynamically, the higher decomposition temperature in the chemical route is due to stronger electron-phonon coupling and the higher value of change in entropy. The variation in the Co-O-Co bond angle reveals Jahn-Teller vibrational anisotropy in the-b plane leading to the anisotropic synthesis behaviour. This anisotropy is the reason for the violation of the paradigm.

In this present work, the influence of sintering temperature (1250 °C and 1275 °C) on the structural and electrical properties of the layered perovskite structured Ruddlesen-Popper class of material SmSrNiO4+δ is studied. The samples are synthesized in single-phase, and tetragonal phase with I4/mmm symmetry is suggested through Rietveld refinement. The microstructural studies reveal the increase in grain size with sintering temperature. The optical studies reveal that the bandgap of the material increases with the increase in sintering temperature.

A new cathode material Pr0.6Ba1.4Co2O6-δ was synthesized by using a conventional solid-state route method using the same conditions as PrBaCo2O6-δ. The XRD analysis shows that the sample is in the orthorhombic phase with Pmmm symmetry having the additional phase of hexagonal BaCoO3. The microstructure reveals that sample is porous as requisite of the cathode material. IV curve is showing the current is increasing with temperature in both samples although it appears after 100 ᵒC in Pr0.6Ba1.4Co2O6-δ. The Grain size and porosity have an impact on the resistivity of the samples as it is higher in the case of Pr0.6Ba1.4Co2O6-δ, which has a larger grain size than PrBaCo2O6-δ.

Lanthanum aluminate (LaAlO 3 ) is one of the promising materials as an electrolyte for SOFCs, which works close to 700 °C. We investigated on Ba doped Lanthanum Strontium Magnesium Aluminate i.e., (La 0.89 Ba 0.01 ) Sr 0.1 Al 0.9 Mg 0.1 O 3-δ (LSBAM01) tape which was obtained by tape casting technique and reaction sintering. In order to determine the conductivity, thickness of the tape was maintained in the range of 100–300 µm using aqueous solution method. The thickness of the tape was set up for ~100 µm. In order to compare the electrical conductivity of tape with the pellet, LSBAM01 powder was prepared by auto-combustion technique. A comparative study of the tape casted specimen and pellet was done in order to find out the effect on green as well as sintered densities of tape and pellet and their corresponding conductivities. The impedance plots showed that the tape was more resistive in comparison to pellet. The conductivity of the tape was found to be reduced in comparison to pellet having the low activation energy than that of tape sample.

TiO2 samples with two different morphology were synthesized via sol–gel and hydrothermal techniques. The effect of synthesis procedure on structural, morphological, optical, and electrical properties was studied. Rietveld analysis revealed that anatase phase having tetragonal structure dominates at room temperature. The presence of anatse phase of TiO2 was further confirmed by the analysis of various peaks obtained from the Raman spectra. The field-emission scanning electron microscopy (FESEM) and transmission electron microscopy micrographs depicted the formation of two different kinds of morphologies with average particle size ranging from 9.87 to 11.35 nm. The FESEM micrographs showed homogeneous particle distribution for sol–gel synthesized sample, whereas it depicted rod-like structure in the sample synthesized via hydrothermal technique. The X-ray photoelectron spectroscopy analysis clearly indicated the presence of appropriate chemical composition and valency states of Ti and O element in TiO2 samples. The optical bandgap was estimated from the UV–visible spectra and found to be in corroboration with the reported values. The conductivity spectra were analyzed using Jonscher power law. The values of activation energy suggested that the conduction mechanism is thermally activated. The conductivity isotherms were scaled through Ghosh scaling model. In the sol–gel synthesized sample, the conduction mechanism was found to be independent of temperature in the entire measured temperature range; however, the hydrothermally synthesized sample depicted that the conduction mechanism is temperature-dependent in the measured temperature range. This discrepancy was understood in terms of structural changes and charge trapping within the structure.

A water-soluble, simple, and facile nitrogen-doped carbon dots (N-CDs) were developed by a single-step via the pyrolysis process and utilized in the fluorometric detection of dopamine (DA). DA is a neurotransmitter and plays a vital role in regulating several biological activities in mammalians. DA can oxidize into DA-quinone by the addition of N-CDs. The emission intensity of N-CDs can be quenched by DA through the inner filter effect (IFE) procedure. This detection mechanism is characterized by UV–vis spectroscopy and fluorescence lifetime decay study. The synthesized N-CDs are highly selective and sensitive towards DA, and their detection limit is 0.2 nM with a linear range of 0.001−1 μM. More importantly, N-CDs are utilizing to detect DA in the human blood serum. The as-synthesized N-CDs have excellent optical properties and are potentially used as a staining material for multicolor cellular imaging of MDA-MB 468 human breast cancer cells. Moreover, N-CDs are also used as a fluorescent ink and can be used for information storage. Hence, the as-synthesized N-CDs are explored as fluorescence materials for DA sensing, multicolor cellular imaging, and fluorescent ink.

We have studied the effects of transition metal (TM) substitution on Fe sub-lattice in Fe 1−x TM x Se 0.5 Te 0.5 (TM ≡ Cr, Mn, Co, Ni and x = 0, 0.01, 0.05, 0.10) in terms of changes in its electronic and magnetic properties. The calculations were performed with the Korringa-Kohn-Rostoker (KKR) Atomic Sphere Approximation (ASA) method within the coherent-potential approximation (CPA). Our spin-polarized calculations show these alloys to be magnetic in nature. We discuss the calculated density of states (DOS), band structures and Fermi surfaces (FS) in terms of the contributions of Fe3d 6 4 s 2 , Cr3d 5 4s 1 , Mn3d 5 4s 2 , Co3d 7 4s 2 , Ni3d 8 4s 2 and Se4s 2 4p 4 outer most electrons. Our results indicate that the effects of doping on the electronic properties are significant with respect to parent FeSe and FeSe 0.5 Te 0.5 superconductor. We have also estimated the value of electron-phonon mass enhancement factor λ (which is the sum of electron–phonon coupling constant and the electron–electron interaction present in the material) to calculate the superconducting transition temperature T c for the TM-doped FeSe 0.5 Te 0.5 . Hopfield parameters are also calculated from the charge self-consistent potentials obtained from KKR-ASA CPA method.

For the perovskite halides, current voltage hysteresis is the biggest puzzle to be solved before industrialization in spite of promising features for future photo-voltaic applications. All the possible causes, from the classical (viz., morphology, defects, slow transient capacitance, etc.) to quantum (viz., spin–orbit interaction) ones, are investigated. However, its origin is still under debate, as possibilities showed some ambiguity on the science known until now. In the present work, we have studied the time dependent photo-conduction behavior of CsPbBr 3 in continuous illumination of AM 1.5 G Sun light for 3 h. We observed a negative differential resistance for a forward scanned current–voltage curve in AM 1.5 G Sun light. Our investigations suggest that the photo-current voltage hysteresis is primarily affected by the thermionic-field emission, which slows down the drift velocity of hot charge carriers with field applications. This study will further lead the scientific community to investigate whether this slowdown in drift velocity is related to the Gunn effect or the Rashba effect.

We have performed ab-initio electronic structure calculations to investigate the ground state properties of Pd1−x Ni x Te (x = 0.0–0.20) alloys. The PdTe and all of its alloys are paramagnetic metals. For low concentrations, the band structure remains almost unchanged and at higher concentrations, a strong redistribution of spectral weights is observed. The most striking feature of the band structure is that the bands around the Fermi energy remain almost unchanged. The calculated Fermi surfaces are remarkably robust against disorder, strongly three-dimensional and have no or negligible nesting. The density of states at Fermi energy increases monotonically with concentration (x). Although the contribution of Ni to the density of states at Fermi energy is increasing continuously yet, Pd and Te dominate the density of states at Fermi energy. The density of states at Fermi energy and superconducting transition temperature T c show opposite trends with respect to Ni concentration. So, density of states at Fermi level alone is not sufficient to discern the trends in T c . We need to know the phonons and electron-phonon interactions as well, which at the moment are not available.

Sodium bismuth titanate, a well-known piezoelectric material is reported as the new family of fast oxide ion conductors. In the current study, we investigated the influence of A-site non-stoichiometry on the electrical conductivity and ion dynamics of sodium bismuth titanate ceramics. For this, we synthesized the system Na0.5+xBi0.5-xTiO3–δ with x = −0.02, −0.01, 0.00, 0.01 and 0.02. The samples synthesized were almost single phase with rhombohedral (R3c) symmetry. The scanning electron micrographs showed the formation of dense grains with bulk density > 96%. The microstructure appeared to be very sensitive to non-stoichiometry. The conductivity data isotherms with frequency showed non-linear variation and were well fitted with Jonscher power law. We have observed super linear frequency dependent behaviour in Bi rich composition and sub-linear behaviour with the increase in Na content. To study the degradation mechanism, Na0.5+xBi0.5-xTiO3-δ (x = −0.01, 0.00, 0.01) samples were kept in reducing environment for 48 h. Further, for the analysis of conduction mechanism and the qualitative/quantitative estimation of charge carriers before and after reducing conditions, various models were used.

The La0.9-xSr0.1Al0.9Mg0.1O3-δ is considered as a promising perovskite to be used as electrolyte in Solid Oxide Fuel Cell due to good ionic conductivity (~10−3 S/cm) with high transference number ~ 0.99. The oxide ionic conductivity can be altered with the critical triangle area which is affected by size and nature of substituent. In the lack of comprehensive study on influence of double-substitution, we have synthesized substituted systems A″xLa0.9-xSr0.1Al0.9Mg0.1O3-δ with x = 0.01, 0.03 and 0.05, here A″ = Ba (aliovalent) and Sm (isovalent) having R 3 ‾ c symmetry. The electrical conductivity data is analyzed using Rice – Roth's free-ion like model for ionic conduction and hopping transport mechanism (Arrhenius model). The defect chemistry suggests that Ba substituted compositions have concentration dependent oxygen content. Whereas, Sm substituted compositions have concentration independent oxygen content. This is verified using thermogravimetric analysis in N2 and O2 atmospheres. Our results also revealed that the aliovalent substitution of Ba effectively increases the ionic conductivity with high transference number, while isovalent substitution of Sm increases the electronic contribution to the total conductivity.

The materials possessing high dielectric constant with high breakdown strength are considered as a potential candidate for the storage of electrostatic energy in capacitors. The ferroelectric materials have high dielectric constant with low dielectric breakdown strength. The samples Ba0.7Sr0.3TiO3 were synthesized by solid state reaction route at different sintering temperatures. The structural studies were employed using XRD with Rietveld refinement and suggest P4mm symmetry. The micro-structural studies reveal the formation of dense grains. Moreover, the water-mark and lamellar features of domain structures observed in micrographs have increased with the increase in sintering temperature. The real part of dielectric permittivity has observed to increase with the increase in sintering temperature. Whereas, phase transition temperature decreased with the increase in sintering temperature. The increase in number of domain structures and reduction in transition temperature led to the increase in the value of piezoelectric coefficient (∼ 133 pC/N).

The structural and electrochemical properties of Sr 1-x Na x SiO 3 were studied. Powders with different compositions (0.1 ≤ x ≤ 0.45) were prepared by solid state reaction. Mixing of SrCO 3 , Na 2 CO 3 and SiO 2 was carried out in different media in order to explore the effect of solvents on the formation of secondary phases. X-ray diffraction was employed to study the phase composition of mixtures treated in air at different temperatures in the range 850–1050 °C for at least 12 h. Various heating schemes were applied to help the incorporation of Na in the monoclinic SrSiO 3 structure. Pressed pellets were sintered at 1000 °C for at least 12 h and electroded with Ag paste for electrochemical characterization. For most compositions and thermal treatments, the formation of the insulating Na 2 Si 2 O 5 phase was observed, as reported in literature. Highest conductivity and degradation rate was obtained when synthesis was carried out in acetone with single calcination step at 850 °C, due to the crystallization of Na 2 Si 2 O 5 from glass. Double calcination limited conductivity but increased its thermal stability. When ethanol was used for powder mixing and double calcination was applied, the material exhibited higher conductivity after long term ageing at 650 °C, also thanks to its low activation energy, without appreciable crystallization of other silicates.

We have studied the effects of transition-metal Cr in excess on the electronic and magnetic properties of FeCr x Se (x = 0.0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.10) alloys. We have used density functional based method Korringa–Kohn–Rostoker atomic sphere approximation within the coherent potential approximation to calculate the densities of states (DOS), band structures and Fermi surfaces (FS) of these alloys. Our calculations show that these alloys ( FeCr x Se ) are non-magnetic. Our unpolarized calculations show a subtle change in terms of density of states, band structure and Fermi surface with respect to the pure FeSe. We have also estimated bare Sommerfeld constant, electron–phonon coupling constant and the superconducting transition temperature T c for these alloys, which were found to be in good agreement with experiments.

An attempt has been made to prepare barium strontium titanate borosilicate glasses in the system, 64[(Ba1−xSrx)·TiO3]–30[2SiO2·B2O3]–5[K2O]–1[Fe2O3] (0.4 ≤ x ≤ 1.0), using the conventional melt-quench method. The prepared glasses were characterized by differential thermal analysis, X-ray diffraction, scanning electron microscopy and impedance spectroscopy techniques. On the basis of the DTA results, the glasses were crystallized via regulated heat treatment process. The activation energy for crystallization was 818 ± 1.6 kJ mol−1. A high dielectric constant of about 107 070 was obtained for the 6 hour heat treated glass ceramic sample. Fe2O3 plays an important role in enhancing crystallization, dielectric constant and retardation of dielectric loss in the samples.

Samarium (Sm3+) doped double perovskite Sr2-xSmxNiMoO6−δ (SSNM) with 0.01 ≤ x ≤ 0.05 is synthesized via citrate-nitrate auto-combustion route. X-ray analysis shows the presence of main phase with tetragonal symmetry and space group I4/m, along with a small amount of SrMoO4 phase. The amount of secondary phase is found to increase with increasing dopant concentration. Micro-structural study reveals the formation of uniform grains with grain growth inhibited by doping. XPS analysis clearly indicates the reduction of Mo6+ to Mo5+. Oxygen vacancies are also found to increase with dopant concentration. Monotonic trends of variation of conductivity and activation energy are observed. In particular, superior conductivity with lower most activation energy is obtained for the sample with x = 0.05. For this composition, impedance measurement is repeated under H2 atmosphere and a significant increase of the conductivity is observed. For air-sintered material, in addition to Mo reduction a new mechanism is proposed, based on the formation of Sr and Mo vacancies which accounts for the effect of doping on lattice parameters, phase composition and conductivity.

We have studied the effects of doping Si and Sb at the Se site in FeSe0.9 (i.e., FeSe0.9-x(Si/Sb)(x) for x - 0, 0.05, 0.10,0.15 and 0.20) using the Korringa-Kohn-Rostoker Atomic Sphere Approximation method within the coherent-potential approximation. Our calculations show that the ground state of FeSe0.9 is nonmagnetic while FeSe0.9-x(Si/Sb)(x) alloys tend to be magnetic. We present the results of unpolarized and spin-polarized, charge self-consistent, calculations for FeSe0.9-x(Si/Sb)(x) alloys in terms of density of states (DOS), band structure and Fermi surface (FS). In particular, we find that the doped FeSe0.9-x exhibits the same topology of the FS as that of FeSe, differing only in subtle FS nesting features in case of unpolarized calculations but in case of spin-polarized calculations, the topology of the FS is very different from that of FeSe. We have also estimated the values of electron-phonon mass enhancement factor lambda (which is the sum of electron-phonon coupling constant as well as the electron-electron interaction) to calculate the superconducting transition temperature T-c for the FeSe0.9-x(Si/Sb)(x) alloys. We find that the calculated T-c are in good agreement with experimental results. (C) 2015 Elsevier B.V. All rights reserved.

This study was envisaged to explore the impact of pesticide solid waste leachate to Allium cepa (common onion) bulbs. Bulbs exposed to the leachate showed hampered root growth and morphological deformities. At 15% and higher concentrations of leachate after 5 days, gall like swellings were noticed around the mitotic zone (zone of root growth). From the dose response curve, the EC50 values for the 5 th , 10 th , 15 th and 20 th day were calculated and the highest EC50 value, 24.9%, was for the 5th day while the lowest EC 50 value, 20%, was for the 20th day. The EC 50 decreases from 5 th to the 20 th day successively. The 5 th day EC50 was used to determine the hazard quotient (HQ) of the pesticide waste leachate from the dumping site. A value of 4.49 as HQ suggests that that there is considerable risk, as any value of HQ above one (>1) is environmentally unacceptable. The response in root growth pattern, residue analysis and the HQ indicates that the leachate is toxic to rot growth of onion and steps for proper management of hazardous waste and leachate are urgently required.

Based on first principles calculations, we show that $Mn$ impurities are magnetic in $MgB_{2}$ due to exchange-splitting of $d_{3z^2-1}$ band and they substantially modify $B$ $p_{\sigma}$ and $p_{\pi}$ bands through hybridization. Thus, $Mn$ impurities could act as strong magnetic scattering centers leading to pair-breaking effects in $MgB_{2}$. In contrast, we find $Fe$ impurities in $MgB_{2}$ to be nearly non-magnetic., Comment: revised version

First-principles, density-functional-based electronic structure calculations are employed to study the changes in the electronic properties of ZnC_{y}Ni_{3} and MgC_{y}Ni_{3} using the Korringa-Kohn-Rostoker coherent-potential approximation method in the atomic sphere approximation (KKR-ASA CPA). As a function of decreasing C at%, we find a steady decrease in the lattice constant and bulk modulus in either alloys. However, the pressure derivative of the bulk modulus displays an opposite trend. Following the Debye model, which relates the pressure derivative of the bulk modulus with the average phonon frequency of the crystal, it can thus be argued that ZnCNi_{3} and its disordered alloys posses a different phonon spectra in comparison to its MgCNi_{3} counterparts. This is further justified by the marked similarity we find in the electronic structure properties such as the variation in the density of states and the Hopfield parameters calculated for these alloys. The effects on the equation of state parameters and the density of states at the Fermi energy, for partial replacement of Mg by Zn are also discussed., 19 pages, 15 figures

High density and long multiwalled carbon nanotubes are deposited using nickel clusters formed from an electrodeposited nickel coating treated by ammonia. Tubes of length 40–50 μm having bamboo shaped structure are aligned nearly parallel to the copper substrate. The inner diameter of the tubes is in the range 20–50 nm. The selected area and nano area diffraction spots clearly show the crystalline nature of nickel clusters. At some locations of the samples in the vicinity of graphite layers, Ni3C phase is also detected. The formation of the Ni3C phase that is unstable at high temperature supports the idea of a vapor–liquid–solid (VLS) mechanism for the growth of the tubes., © Elsevier

We examine the mathematical and physical basis for choosing the coefficients of an Ising model Hamiltonian, variably known as multisite interactions or effective cluster interactions, used in the study of phase stability of substitutionally disordered alloys. We show that concentration-independent interactions can be defined if and only if the system is assumed to be strictly finite, i.e., to contain a finite number of sites. If the system is infinite, only concentration-dependent interactions can be defined. This strict dichotomy has apparently been missed in previous discussions, and this oversight has led both to erroneous conclusions regarding the relationships between the two types of interactions, and to confusion about methods for determining them. Explicitly, no relationship between the two sets of interactions can exist since these two different types of interactions cannot be defined simultaneously. We also discuss the physical basis for the mapping of alloy configurational energies onto the Hamiltonian of an Ising model, and point out that the use of the model involves the generally unjustified assumption that the kinetics properties of an alloy will allow configurational transformations to occur according to the dictates of the equilibrium thermodynamics of a spin system. In a final section, we present the implications of our results to the study of alloy phase stability and transformations by means of the Ising model.

Two approaches for obtaining tight-binding parameters for metallic alloys are compared and contrasted with special regard for the application to large scale simulations such as may occur in tight-binding molecular dynamics studies.

We study the effects of relativity on the electronic structure of Hg as it evolves from an atom to a cluster, and then to the bulk. A comparison of nonrelativistic and scalar-relativistic results for bulk Hg, obtained self-consistently, clearly shows the importance of including the relativistic terms as well as treating the 5[ital d] electrons as valencelike. Our cluster calculations show that the relativistic effects are equally important for clusters, and that the differences in many electronic properties such as the size dependence of the gap energy and the [ital l] character of Hg clusters with respect to other divalent-metal clusters, for example, Be and Mg, arise due to the relativistic terms, thus providing further insight into the electronic origins of these properties.

We report here our study on SiC doped with transition metals using first principle density functional theory calculations. We have considered cubic SiC with 3d transition metals as substitutional impurities for Si and C site separately. Cubic SiC doped with Cr, Mn, show ferromagnetism whereas with Sc, Ti, V and Co show site dependency of magnetic properties. Rests of the impurities are found to be non-magnetic., Presented in the 55th DAE-Solid State Physics Symposium, 26th to 30th December, 2010, Manipal University, Manipal, India; AIP Conf. Proc. 1349, 1087-1088 (2011)

We present the first implementation of a unified approach to the study of alloys, using the atomic-sphere approximation formulation of the Korringa-Kohn-Rostoker coherent potential approximation method [P. P. Singh and A. Gonis, Phys. Rev. B 48, 1989 (1993)], which allows the treatment of the disordered alloy and of the ordered alloys on an equal footing. We apply this method to the study of the phase stability of the Ni-Pt alloy and resolve a number of discrepancies that have arisen in recent studies of this system.

We describe a consistent approach for applying the coherent-potential approximation (CPA) to the various representations of the linear muffin-tin orbital method. Unlike the previous works of Kudrnovsky [ital et] [ital al]. [Phys. Rev. B 35, 2487 (1987); 41, 7515 (1990)], our results for the ensemble-averaged Green functions in the tight-binding representation yield [ital E]- and [bold r]-dependent quantities that are consistent with the traditional applications of the single-site CPA. To illustrate the reliability and the usefulness of our approach we compare the nonspherically averaged charge densities, calculated in real space, of ordered NiPt in [ital L]1[sub 0] structure and the substitutionally disordered Ni[sub 0.5]Pt[sub 0.5] on a face-centered-cubic lattice.

A Comment on the Letter by Myung Joon Han and Sergey Y. Savrasov, Phys. Rev. Lett. 103, 067001 (2009). The authors of the Letter offer a Reply.

We have extended the recently formulated Korringa-Kohn-Rostoker coherent-potential approximation (KKR-CPA) for the treatment of substitutionally disordered alloys within the KKR atomic-spheres approximation (ASA) to include charge self-consistency. To test the accuracy of the present approach we have carried out self-consistent-field (SCF) KKR-ASA-CPA calculations of Cu-Pd alloys. Our results are in good agreement with experimental results and previous SCF-KKR-CPA calculations. We also present a comparison of the electronic structures of the ordered with the disordered Cu-Pd alloys.