Deposition and characterization of pure and Cd doped SnO2 thin films by the nebulizer spray pyrolysis (NSP) technique

Pure and cadmium doped tin oxide thin films were deposited on glass substrates from aqueous solution of cadmium acetate, tin (IV) chloride and sodium hydroxide by the nebulizer spray pyrolysis (NSP) technique. X-ray diffraction reveals that all films have tetragonal crystalline structure with preferential orientation along (200) plane. On application of the Scherrer formula, it is found that the maximum size of grains is 67 nm. Scanning electron microscopy shows that the grains are of rod and spherical in shape. Energy dispersive X-ray analysis reveals the average ratio of the atomic percentage of pure and Cd doped SnO2 films. The electrical resistivity is found to be 10(2) Omega cm at higher temperature (170 degrees C) and 10(3) Omega cm at lower temperature (30 degrees C). Optical band gap energy was determined from transmittance and absorbance data obtained from UV-vis spectra. Optical studies reveal that the band gap energy decreases from 3.90 eV to 3.52 eV due to the addition of Cd as dopant with different concentrations.

Growth-temperature dependent physical properties of SnS nanocrystalline thin films

In this article we have demonstrated the influence of growth-temperature on the morphology and orientation of SnS films deposited by thermal evaporation technique. While increasing the growth-temperature, the morphology of SnS films changed from flakes-like nanocrystals to regular cubes, whereas their orientation shifted from <111> to <040> direction. The chemical composition of SnS films gradually changed from sulfur-rich to tin-rich with the increase of growth-temperature. The structural analyzes reveal that the crystal structure of SnS films probably changes from orthorhombic to tetragonal at the growth-temperature of about 410 degrees C. Raman studies show that SnS films grown at all temperatures consist of purely SnS phase, whereas the optical studies reveal that the direct optical bandgap of SnS films decreased with the increase of growth-temperature. From these results it has been emphasized that the morphology and orientation along with electrical and optical properties of nearly stoichiometric SnS films strongly depend on their growth-temperature.

Phase chemistry of the system Nb-Rh-O

Phase relations in the system Nb-Rh-O at 1223 K were investigated by isothermal equilibration of eleven compositions and analysis of quenched samples using OM, XRD, SEM and EDS. The oxide phase in equilibrium with the alloy changes progressively from NbO to NbO2, NbO2.422 and Nb2O5-x with increasing Rh. Only one ternary oxide NbRhO4 with tetragonal structure (a=0.4708 nm and c=0.3017 nm) was detected. It coexists with Rh and Nb2O5. The standard Gibbs energy of formation of NbRhO4 from its component binary oxides measured using a solid-state electrochemical cell can be represented by the equation; Delta G(f,ox)(o)(J/mol) = -38,350 + 5.818 x T(+/- 96) Constructed on the basis of thermodynamic information of the various alloy and oxide phases are oxygen potential diagram for the system Nb-Rh-O at 1223 K and temperature-composition diagrams at constant partial pressures of oxygen.

Factors influencing stick-slip motion: effect of hardness, crystal structure and surface texture

In the present investigation, efforts were made to study the different frictional responses of materials with varying crystal structure and hardness during sliding against a relatively harder material of different surface textures and roughness. In the experiments, pins were made of pure metals and alloys with significantly different hardness values. Pure metals were selected based on different class of crystal structures, such as face centered cubic (FCC), body centered cubic (BCC), body centered tetragonal (BCT) and hexagonal close packed (HCP) structures. The surface textures with varying roughness were generated on the counterpart plate which was made of H-11 die steel. The experiments were conducted under dry and lubricated conditions using an inclined pin-on-plate sliding tester for various normal loads at ambient environment. In the experiments, it was found that the coefficient of friction is controlled by the surface texture of the harder mating surfaces. Further, two kinds of frictional response, namely steady-state and stick-slip, were observed during sliding. More specifically, stead-state frictional response was observed for the FCC metals, alloys and materials with higher hardness. Stick-slip frictional response was observed for the metals which have limited number of slip systems such as BCT and HCP. In addition, the stick-slip frictional response was dependent on the normal load, lubrication, hardness and surface texture of the counterpart material. However, for a given kind of surface texture, the roughness of the surface affects neither the average coefficient of friction nor the amplitude of stick-slip oscillation significantly.

Sol-gel Processed Cu2SnS3 Films for Photovoltaics

Cu2SnS3 films have been processed by the sol-gel route. Differential Scanning Calorimetry (DSC) study was done to observe the phase transformations and to ascertain the deposition temperature. X-ray diffraction (XRD) confirms the phase formation of Cu2SnS3. The texture coefficient analysis shows the preferential orientation of the (112) facet. Scanning electron microscopy reveals the morphology of the film Energy Dispersive Spectroscopy (EDS) was used for compositional studies. Raman spectrum shows the peaks corresponding to the tetragonal phase of Cu2SnS3.

Polymorphic phase boundaries and enhanced piezoelectric response in extended composition range in the lead free ferroelectric BaTi1-xZrxO3

Neutron powder diffraction study of Ba(Ti1-xZrx)O-3 at close composition intervals has revealed coexistence of ferroelectric phases: orthorhombic (Amm2) + tetragonal (P4mm) for 0.02 <= x <= 0.05 and rhombohedral (R3m) + orthorhombic (Amm2) for 0.07 <= x < 0.09. These compositions exhibit relatively enhanced piezoelectric properties as compared to their single phase counterparts outside this composition region, confirming the polymorphic phase boundary nature of the phase coexistence regions. (C) 2013 AIP Publishing LLC.

Metastable morphotropic phase boundary state in the multiferroic BiFeO3-PbTiO3

Temperature-time study of the magnetoelectric multiferroic (1-x)BiFeO3-(x)PbTiO3 by x-ray and electron diffraction on the reported morphotropic phase boundary (MPB) compositions revealed that this MPB does not correspond to the equilibrium state. The MPB like state is rather of metastable nature and arise due to kinetic arrest of metastable rhombohedral (R3c) phase, along with the equilibrium tetragonal (P4mm) phase. The life time of the metastable R3c nuclei is very sensitive to composition and temperature, and nearly diverges at x -> 0.27. The MPB like state appears only if the system is cooled before the metastable R3c nuclei could vanish. These findings resolve the long standing controversy with regard to seemingly erratic phase formation behaviour reported by different groups and provides a rational basis for developing genuine equilibrium MPB compositions in this system for better piezoelectric properties. (C) 2013 AIP Publishing LLC.

Melting and solidification behavior of Pb-Sn embedded alloy nano-particles

Nano-sized bimetallic dispersoids consisting of (Pb) and beta-(Sn) phases of eutectic composition (Pb26.1Sn73.9) embedded in aluminum and Al-Cu-Fe quasicrystalline matrices have been prepared by rapid solidification processing. The two phases, face centered cubic (Pb) and body center tetragonal, beta-(Sn) solid solution co-exist in all the embedded nanoparticles at room temperature. The phases bear crystallographic orientation relationship with the matrix. In situ TEM study has been carried out for the alloy particles to study the melting and the solidification behavior. The detailed microscopic observations indicate formation of a single-phase metastable fcc (Pb) in the nano-particles prior to the melting during heating. Solidification of these particles begins with nucleation of fcc (Pb), which phase separates into fcc (Pb) and beta-(Sn) lamellae in the solid state. In situ X-ray diffraction study is carried out to obtain lattice parameter of metastable fcc (Pb) and thereby an estimate of amount of Sn dissolved in the metastable (Pb) prior to the melting. The results are discussed in terms of a metastable phase diagram between fcc Pb and fcc Sn and invoking the size effect on the metastable phase diagram. The size factor is found to play a critical role in deciding the pathway of phase transformation as well as the extension of solid solubility of Sn in fcc (Pb) in the nano-particles.

Long ranged structural modulation in the pre-morphotropic phase boundary cubic-like state of the lead-free piezoelectric Na1/2Bi1/2TiO3-BaTiO3

The nature of the pre-morphotropic phase boundary (MPB) cubic-like state in the lead-free piezoelectric ceramics (1-x)Na1/2Bi1/2TiO3-(x)BaTiO3 at x similar to 0.06 has been examined in detail by electric field and temperature dependent neutron diffraction, x-ray diffraction, dielectric and ferroelectric characterization. The superlattice reflections in the neutron diffraction patterns cannot be explained with the tetragonal P4bm and the rhombohedral (R3c) phase coexistence model. The cubic like state is rather a result of long ranged modulated complex octahedral tilt. This modulated structure exhibits anomalously large dielectric dispersion. The modulated structure transforms to a MPB state on poling. The field-stabilized MPB state is destroyed and the modulated structure is restored on heating the poled specimen above the Vogel-Fulcher freezing temperature. The results show the predominant role of competing octahedral tilts in determining the nature of structural and polar states in Na1/2Bi1/2TiO3-based ferroelectrics. (C) 2013 AIP Publishing LLC.

Dielectric relaxation, phase transition and Rietveld studies of perovskite Pb0.94Sr0.06](Mn1/3Sb2/3)(0.05)(Zr0.52Ti0.48)(0.95)]O-3 ceramics

The frequency-dependent dielectric relaxation of Pb0.94Sr0.06](Mn1/3Sb2/3)(0.05)(Zr0.52Ti0.48)(0.95)]O-3 ceramics, synthesized in pure perovskite phase by a solid-state reaction technique is investigated in the temperature range from 303 to 773 K by alternating-current impedance spectroscopy. Using Cole-Cole model, an analysis of the imaginary part of the dielectric permittivity with frequency is performed assuming a distribution of relaxation times. The scaling behavior of the imaginary part of the electric modulus suggests that the relaxation describes the same mechanism at various temperatures. The variation of dielectric constant with temperature is explained considering the space-charge polarization. The SEM indicates that the sample has single phase with an average grain size similar to 14.2 mu m. The material exhibits tetragonal structure. A detailed temperature dependent dielectric study at various frequencies has also been performed. (C) 2013 Elsevier B.V. All rights reserved.

The effect of multisubstitution on the thermoelectric properties of chalcogenide-based Cu2.1Zn0.9Sn1-xInxSe4 (0 <= x <= 0.1)

Quinary chalcogenide compounds Cu2.1Zn0.9Sn1-xInxSe4 (0 <= x <= 0.1) were prepared by melting (1170K) followed by annealing (773 K) for 172 h. Powder X-ray diffraction (XRD) data accompanied by electron probe microanalysis (EPMA) and Raman spectra of all the samples confirmed the formation of a tetragonal kesterite structure with Cu2FeSnS4-type. The thermoelectric properties of all the samples were measured as a function of temperature in the range of 300-780K. The electrical resistivity of all the samples exhibits metallic-like behavior. The positive values of the Seebeck coefficient and the Hall coefficient reveal that holes are the majority charge carriers. The codoping of copper and indium leads to a significant increase of the electrical resistivity and the Seebeck coefficient as a function of temperature above 650 K. The thermal conductivity of all the samples decreases with increasing temperature. Lattice thermal conductivity is not significantly modified as the doping content may infer negligible mass fluctuation scattering for copper/zinc and indium/tin substitution. Even though, the power factors (S-2/rho) of indium-doped samples Cu2.1Zn0.9Sn1-xInxSe4 (x = 0.05, 0.075) are almost the same, the maximum zT = 0.45 at 773K was obtained for Cu2.1Zn0.9Sn0.925In0.075Se4 due to its smaller value of thermal conductivity. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Anomalous magnetism of Pr in PrCoAsO

Detailed magnetization and magneto-transport measurements studies are carried out to unearth the anomalous magnetism of Pr in PrCoAsO compound. The studied PrCoAsO sample is single phase and crystallized in the tetragonal structure with space group P4/nmm in analogy of ZrCuSiAs type compounds. Detailed magnetization measurements showed that Co moments in PrCoAsO exhibit weakly itinerant ferromagnetic Co spins ordering at below 80 K with a small magnetic moments of similar to 0.12 mu B/f.u. High temperatures Curie-Weiss fit, resulted in effective paramagnetic moment mu(eff) (exp) of 5.91 mu(B)/f.u., which can be theoretically assigned to 3d Co (3.88 mu(B)) and 4f Pr (3.58 mu(B)). Further, a positive Curie-Weiss temperature (Theta) of 136 K is seen, indicating predominant ferromagnetic interactions in PrCoAsO. Detailed transport measurements showed that PrCoAsO exhibit metallic behavior and negative magneto-resistance below ferro-magnetically (FM) ordered state. Surprisingly, the situation of PrCoAsO is similar to non magnetic La containing LaCoAsO and strikingly different than that as reported for magnetic Nd, Sm and Gd i.e., (Nd/Sm/Gd)CoAsO. The magnetic behavior of PrCoAsO being closed to LaCoAsO and strikingly different to that of (Nd/Sm/Gd)CoAsO is unusual. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Structural, Electrical and Magnetic Behaviour of FeTe0.5Se0.5 Superconductor

We report the synthesis as well as structural and physical properties of the bulk polycrystalline FeTe and FeTe0.5Se0.5 compounds. These samples are synthesised by the solid state-reaction method via vacuum encapsulation. Both studied compounds are crystallized in a tetragonal phase with space group P4/nmm. The parent FeTe compound shows an anomaly in resistivity measurement at around 78 K, which is due to the structural change along with a magnetic phase transition. The superconductivity in the FeTe0.5Se0.5 sample at 13 K is confirmed by the resistivity measurements. DC magnetisation along with an isothermal (M-H) loop shows that FeTe0.5Se0.5 possesses bulk superconductivity. The upper critical field is estimated through resistivity rho (T,H) measurements using Gingzburg-Landau (GL) theory and is above 50 T with 50 % resistivity drop criterion. The origin of the resistive transition broadening under magnetic field is investigated by thermally activated flux flow. The magnetic field dependence of the activation energy of the flux motion is discussed.

Structural and thermodynamic properties of Fe1.12Te with multiple phase transitions

The parent compound of iron chalcogenide superconductors, Fe1+yTe, with a range of excess Fe concentrations exhibits intriguing structural and magnetic properties. Here, the interplay of magnetic and structural properties of Fe1.12Te single crystals have been probed by low-temperature synchrotron X-ray powder diffraction, magnetization, and specific heat measurements. Thermodynamic measurements reveal two distinct phase transitions, considered unique to samples possessing excess Fe content in the range of 0.11 <= y <= 0.13. On cooling, an antiferromagnetic transition, T-N approximate to 57K is observed. A closer examination of powder diffraction data suggests that the transition at TN is not purely magnetic, but accompanied by the commencement of a structural phase transition from tetragonal to orthorhombic symmetry. This is followed by a second prominent first-order structural transition at T-S with T-S < T-N, where an onset of monoclinic distortion is observed. The results point to a strong magneto-structural coupling in this material. (C) 2014 AIP Publishing LLC.

Ferroelectric and optical properties of Ba5Li2Ti2Nb8O30 ceramics potential for memory applications

Giant grained (42 mu m) translucent Ba5Li2Ti2Nb8O30 ceramic was fabricated by conventional sintering technique using the powders obtained via solid state reaction route. These samples were confirmed to possess tetragonal tungsten bronze structure (P4bm) at room temperature. The scanning electron microscopy established the average grain size to be close to 20 mu m. The photoluminescence studies carried out on these ceramics indicated sharp emission bands around 433 and 578 nm at an excitation wavelength of 350 nm which were attributed to band-edge emission as the band gap was 2.76 eV determined by Kubelka-Munk function. The dielectric properties of these ceramics were studied over wide frequency range (100-1 MHz) at room temperature. The decrease in dielectric constant with frequency could be explained on the basis of Koops theory. The dielectric constant and the loss were found to decrease with increasing frequency. The Curie temperature was confirmed to be similar to 370 A degrees C based on the dielectric anomaly observed when these measurements were carried out over a temperature range of 30-500 A degrees C. This shows a deviation from Curie-Weiss behaviour and hence an indicator of the occurrence of disordering in the system, the gamma = 1.23 which confirms the diffuse ferroelectric transition. These ceramics at room temperature exhibited P-E hysteresis loops, though not well saturated akin to that of their single crystalline counterparts. These are the suitable properties for ferroelectric random access memory applications.