The effect of Se doping on spectroscopic and electrical properties of GeTe

Selenium doped thin films of GeTe alloys were investigated for their structural modifications by X-ray Diffraction, Fourier Transform Infrared Spectroscopy, X-ray photoelectron Spectroscopy (XPS) and Raman Spectroscopy. The band gap increase from 0.69 to 1.10 eV with increasing Se addition signifies the possibility of band gap tuning in the material. Disorder decreases, band widens and conductivity saturates about 0.20 at.% of Se addition. Structural changes are explained by the bond theory of solids. The as-deposited films are amorphous and 0.50 at.% Se alloy forms a homogeneous amorphous phase with a mixture of Ge-Se and Te-Se bonds. The XPS core level spectra and Raman spectra investigation clearly indicate the formation of Ge-Se, GeTe2 and Te-Se bonds with Se addition. Crystallization temperature is found to be increasing with Se and the 0.10 at.% Se alloy is found to have a higher resistance contrast compared to other Se concentration alloys. Up to 0.10 at.% of Se addition can enhance GeTe phase change memory properties. (C) 2013 Elsevier B.V. All rights reserved.

Mechanical and electronic properties of pristine and Ni-doped Si, Ge, and Sn sheets

Silicene, a graphene analogue of silicon, has been generating immense interest due to its potential for applications in miniaturized devices. Unlike planar graphene, silicene prefers a buckled structure. Here we explore the possibility of stabilizing the planar form of silicene by Ni doping using first principles density functional theory based calculations. It is found that planar as well as buckled structure is stable for Ni-doped silicene, but the buckled sheet has slightly lower total energy. The planar silicene sheet has unstable phonon modes. A comparative study of the mechanical properties reveals that the in-plane stiffness of both the pristine and the doped planar silicene is higher compared to that of the buckled silicene. This suggests that planar silicene is mechanically more robust. Electronic structure calculations of the planar and buckled Ni-doped silicene show that the energy bands at the Dirac point transform from linear behavior to parabolic dispersion. Furthermore, we extend our study to Ge and Sn sheets that are also stable and the trends of comparable mechanical stability of the planar and buckled phases remain the same.

Hydrothermal synthesis of Gd2O3:Eu3+ nanophosphors: Effect of surfactant on structural and luminescence properties

Various morphologies of Eu3+ activated gadolinium oxide have been prepared by hydrothermal method using hexadecylamine (HDA) as surfactant at different experimental conditions. The powder X-ray diffraction studies reveal as-formed product is hexagonal Gd(OH)(3):Eu3+ phase and subsequent heat treatment at 350 and 600 degrees C transforms to monoclinic GdOOH:Eu3+ and cubic Gd2O3:Eu3+ phases respectively. SEM pictures of without surfactant show irregular shaped rods along with flakes. However, in the presence of HDA surfactant, the particles are converted into rods of various sizes. The temperature dependent morphological evolution of Gd2O3:Eu3+ without and with HDA surfactant is studied. TEM micrographs of Gd(OH)(3):Eu3+ sample with HDA confirms smooth nanorods with various diameters in the range 20-100 nm. FTIR studies reveal that HDA surfactant plays an important role in conversion of cubic to hexagonal phases. Among these three phases, cubic phase Gd2O3:Eu3+ (lambda(ex) = 254 nm) show red emission at 612 nm corresponding to D-5(0)-> F-7(2) and is more efficient host than the monoclinic counterpart. The band gap for hexagonal Gd(OH)(3):Eu3+ is more when compared to monoclinic GdOOH:Eu3+ and cubic Gd2O3:Eu3+. (C) 2013 Elsevier B. V. All rights reserved.

Effect of the Addition of B2O3 on the Density, Microstructure, Dielectric, Piezoelectric and Ferroelectric Properties of K0.5Na0.5NbO3 Ceramics

Boron oxide (B2O3) addition to pre-reacted K0.5Na0.5NbO3 (KNN) powders facilitated swift densification at relatively low sintering temperatures which was believed to be a key to minimize potassium and sodium loss. The base KNN powder was synthesized via solid-state reaction route. The different amounts (0.1-1 wt%) of B2O3 were-added, and ceramics were sintered at different temperatures and durations to optimize the amount of B2O3 needed to obtain KNN pellets with highest possible density and grain size. The 0.1 wt% B2O3-added KNN ceramics sintered at 1,100 A degrees C for 1 h exhibited higher density (97 %). Scanning electron microscopy studies confirmed an increase in average grain size with increasing B2O3 content at appropriate temperature of sintering and duration. The B2O3-added KNN ceramics exhibited improved dielectric and piezoelectric properties at room temperature. For instance, 0.1 wt% B2O3-added KNN ceramic exhibited d (33) value of 116 pC/N which is much higher than that of pure KNN ceramics. Interestingly, all the B2O3-added (0.1-1 wt%) KNN ceramics exhibited polarization-electric field (P vs. E) hysteresis loops at room temperature. The remnant polarization (P (r)) and coercive field (E (c)) values are dependent on the B2O3 content and crystallite size.

Size dependent structural relaxations and dielectric properties induced by surface functionalized MWNTs in poly(vinylidene fluoride)/poly(methyl methacrylate) blends

Structural dynamics, dielectric permittivity and ferroelectric properties in poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) (PVDF/PMMA) blends with respect to crystalline morphology was systematically investigated in presence of amine functionalized MWNTs (NH2-MWNTs) using dielectric spectroscopy. The crystalline morphology and the crystallization driven demixing in the blends was assessed by light microscopy (LM), wide angle X-ray diffraction (WXRD) and, in situ, by shear rheology. The crystal nucleation activity of PVDF was greatly induced by NH2-MWNTs, which also showed two distinct structural relaxations in dielectric loss owing to mobility confinement of PVDF chains and smaller cooperative lengths. The presence of crystal-amorphous interphase was supported by the presence of interfacial polarization at lower frequencies in the dielectric loss spectra. On contrary, the control blends showed a single broad relaxation at higher frequency due to defective crystal nuclei. This was further supported by monitoring the dielectric relaxations during isothermal crystallization of PVDF in the blends. These observations were addressed with respect to the spherulite sizes which were observed to be larger in case of blends with NH2-MWNTs. Higher dielectric permittivity with minimal losses was also observed in blends with NH2-MWNTs as compared to neat PVDF. Polarization obtained using P-E (polarization-electric field) hysteresis loops was higher in case of blends with NH2-MWNTs in contrast to control blends and PVDF. These observations were corroborated with the charge trapped at the crystal-amorphous interphase and larger crystal sizes in the blends with NH2-MWNTs. The microstructure and localization of MWNTs were assessed using SEM.

Nanostructured CexZn1-xO thin films: Influence of Ce doping on the structural, optical and electrical properties

Thin films of CexZn1-xO thin films were deposited on glass substrates at 400 degrees C by nebulizer spray pyrolysis technique. Ce doping concentration (x) was varied from 0 to 10%, in steps of 2.5%. X-ray diffraction reveals that all the films have polycrystalline nature with hexagonal crystal structure and high preferential orientation along (002) plane. Optical parameters such as; transmittance, band gap energy, refractive index (n), extinction coefficient (k), complex dielectric constants (epsilon(r), epsilon(i)) and optical conductivity (sigma(r), sigma(i)) have been determined and discussed with respect to Ce concentration. All the films exhibit transmittance above 80% in the wavelength range from 330 to 2500 nm. Optical transmission measurements indicate the decrease of direct band gap energy from 3.26 to 3.12 eV with the increase of Ce concentration. Photoluminescence spectra show strong near band edge emission centered similar to 398 nm and green emission centered similar to 528 nm with excitation wavelength similar to 350 nm. High resolution scanning electron micrographs indicate the formation of vertical nano-rod like structures on the film surface with average diameter similar to 41 nm. Electrical properties of the Ce doped ZnO film have been studied using ac impedance spectroscopy in the frequency range from 100 Hz-1 MHz at different temperatures. (C) 2013 Elsevier B.V. All rights reserved.

Thermal and Sonochemical Degradation Kinetics of Poly(n-butyl methacrylate-co-alkyl acrylates): Variation of Chain Strength and Stability with Copolymer Composition

The thermal degradation of poly(n-butyl methacrylate-co-alkyl acrylate) was compared with ultrasonic degradation. For this purpose, different compositions of poly (n-butyl methacrylate-co-methyl acrylate) (PBMAMA) and a particular composition of poly(n-butyl methacrylate-co-ethyl acrylate) (PBMAEA) and poly(n-butyl methacrylate-co-butyl acrylate) (PBMABA) were synthesized and characterized. The thermal degradation of polymers shows that the poly(alkyl acrylates) degrade in a single stage by random chain scission and poly(n-butyl methacrylate) degrades in two stages. The number of stages of thermal degradation of copolymers was same as the majority component of the copolymer. The activation energy corresponding to random chain scission increased and then decreased with an increase of n-butyl methacrylate fraction in copolymer. The effect of methyl acrylate content, alkyl acrylate substituent, and solvents on the ultrasonic degradation of these copolymers was investigated. A continuous distribution kinetics model was used to determine the degradation rate coefficients. The degradation rate coefficient of PBMAMA varied nonlinearly with n-butyl methacrylate content. The degradation of poly (n-butyl methacrylate-co-alkyl acrylate) followed the order: PBMAMA < PBMAEA < PBMABA. The variation in the degradation rate constant with composition of the copolymer was discussed in relation to the competing effects of the stretching of the polymer in solution and the electron displacement in the main chain. (C) 2012 Society of Plastics Engineers

Self propagating combustion synthesis and luminescent properties of nanocrystalline CeO2: Tb3+ (1-10 mol%) phosphors

Undoped and Tb3+ (1-10 mol%) doped CeO2 nanophosphors were synthesized by low temperature solution combustion method. The combustion derived products were well studied by Powder X-ray diffraction (PXRD), Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and Ultraviolet visible (UV-Vis) characterizations. The thermoluminescence (TL) glow curves of CeO2: Tb3+ (1-10 mol%) nanophosphors exposed to c source (60Co) for various doses were discussed for the first time. Two TL glow peaks recorded at 182 and 262 degrees C respectively. The TL intensity at 262 degrees C peak increases linearly in the dose range 0.5-7 kGy. Further, this peak was well defined, intense and glow peak structure does not change with c-dose as a result, it was quite useful in TL dosimetry of ionizing radiations. The kinetic parameters associated with the glow peak were estimated using Chen's half width method. The photoluminescence emission (PLE) spectra consists of characteristic peaks at 544 and 655 nm which were attributed to D-5(4) -> F-7(5) and D-5(4) -> F-7(2) transitions of Tb3+ ions. The optimal concentration of Tb3+ ions was found to be 7 mol%. The color co-ordinates of CeO2: Tb3+ (1-10 mol%) located in green region. Hence, this phosphor was quite useful for display applications. (C) 2013 Elsevier B. V. All rights reserved.

Correlations between mechanical and photoluminescence properties in Eu doped sodium bismuth titanate

Nanoindentation technique is utilized to examine mechanical property variation in Eu doped Na0.5Bi0.5 TiO3 (NBT). Doping levels of Eu in NBT is systematically varied. Dilute doping results in a linear reduction in both modulus and hardness. At higher concentrations, a recovery of the mechanical properties (to undoped NBT values) is observed. These experimental trends mirror variations in the optical emission intensities with Eu concentration. Observed trends are rationalized on the basis of a model, which hypothesizes phase segregation beyond a critical Eu doping level. Such segregation leads to the formation of pure NBT, nano-Eu saturated NBT, and nano-mixed Eu oxides in the microstructure. Pure NBT is optically inactive, while saturated Eu:NBT is a much better emitter when compared to europium oxide. Hence beyond the critical concentration, luminescence signal comes primarily from the saturated Eu:NBT phase. The model presented is supported by nanoindentation, and spectroscopic results. (C) 2013 Elsevier Ltd. All rights reserved.

Optical, Electrochemical, and Structural Properties of Spray Coated Dihexyl Substituted Poly (3,4 propylene dioxythiophene) Film for Optoelectronics Devices

The dihexyl substituted poly (3,4-propylenedioxythiophene) (PProDOT-Hx(2)) thin films uniformly deposited by cost effective spray coating technique on transparent conducting oxide coated substrates. The electro-optical properties of PProDOT-Hx(2) films were studied by UV-Vis spectroscopy that shows the color contrast about 45% with coloration efficiency of approximate to 185cm(2)/C. The electrochemical properties of PProDOT-Hx(2) films were studied by cyclic voltammetry and AC impedance techniques. The cyclic voltammogram shows that redox reaction of films are diffusion controlled and ions transportation will be faster on the polymer film at higher scan rate. Impedance spectra indicate that polymer films are showing interface charge transfer process as well as capacitive behavior between the electrode and electrolyte. The XRD of the PProDOT-Hx(2) thin films revealed that the films are in amorphous nature, which accelerates the transportation of ions during redox process.

Synthesis, structural and thermoluminescence properties of YAlO3:Dy3+ nanophosphors

Thermoluminescence properties of YAlO3:Dy3+ nanophosphor prepared by a low temperature solution combustion (SC) method using oxalyl dihydrazide as a fuel were studied and the results were compared to bulk phosphor prepared by solid state (SS) synthesis. Powder X-ray diffraction patterns confirm the orthorhombic phase of SC and SS methods. Rietveld refinement was used to estimate the cell parameters of undoped and Dy3+ doped YAlO3. Scanning electron micrographs reveal dumbbell shape particles. Electron paramagnetic resonance spectra of YAlO3:Dy3+ nanophosphors were studied at 293 K, 77 K and 10 K. Thermoluminescence responses of SC and SS prepared phosphor were studied using gamma irradiation in the dose range 0.1-6 kGy at a warming rate of 1 degrees C s (1) at room temperature (RT). The optimized concentrations of Dy3+ ions in YAlO3 was found to be 3 mol%. The trapping parameters (i. e. activation energy, frequency factor, order of kinetic) of all the individual peaks of the glow curves have been analysed by using Chen's method. The low fading and linear response in the wide range (0.1-1 kGy) suggests the possibility of usage of SC prepared phosphor in dosimeter applications. (C) 2013 Elsevier B. V. All rights reserved.

Microstructural evolution and mechanical properties of Mg composites containing nano-B4C hybridized micro-Ti particulates

In this work, the microstructural evolution and mechanical properties of extruded Mg composites containing micro-Ti particulates hybridized with varying contents of nano-B4C are investigated, and compared with Mg-5.6Ti. Microstructural characterization showed the presence of uniformly distributed micro-Ti particles embedded with nano-B4C particulates that resulted in significant grain refinement. Electron back scattered diffraction (EBSD) analyses of Mg-(5.6Ti + x-B4C)(BM) hybrid composites showed that the addition of hybridized particle resulted in relatively more recrystallized grains, realignment of basal planes and extension of weak basal fibre texture when compared to Mg-5.6Ti. The evaluation of mechanical properties indicated improved strength with ductility retention in Mg-(5.6Ti + x-B4C)(BM) hybrid composites. When compared to Mg-5.6Ti, the superior strength properties of the Mg-(5.6Ti + xB(4)C)(BM) hybrid composites are attributed to the presence of nano-reinforcements, the uniform distribution of the hybridized particles, better interfacial bonding between the matrix and the reinforcement particles and the matrix grain refinement achieved by nano-B4C addition. The ductility enhancement obtained in hybrid composites can be attributed to the fibre texture spread and favourable basal plane orientation achieved due to nano B4C addition. (C) 2013 Elsevier B.V. All rights reserved.

Effect of pH on structural and magnetic properties of nanocrystalline Y3Fe5O12 by aqueous co-precipitation method

The Y3Fe5O12 (YIG) nanopowders were synthesised at different pH using co-precipitation method. The effect of pH on the phase formation of YIG is characterised using XRD, TEM, FTIR and TG/DTA. From the Scherer formula, the particle sizes of the powders were found to be 13, 19 and 28 nm for pH=10, 11 and 12 respectively. It is found that as the pH of the solution increase the particle size is also increases. It is also clear from the TG/DTA curves that as the pH is increasing the weight losses were found to be small. The nanopowders were sintered at 600, 700, 800 and 900 degrees C for 5 h using conventional sintering method. The phase formation is completed at 800 degrees C/5 h which is correlated with TG/DTA. The average grain size of the samples is found to be similar to 161 nm. The high values of M-s=23 emu g(-1) and H-c=22 Oe were recorded for the sample sintered at 900 degrees C.

Low temperature and self catalytic growth of ultrafine ITO nanowires by electron beam evaporation method and their optical and electrical properties

We report the self catalytic growth of Sn-doped indium oxide (ITO) nanowires (NWs) over a large area glass and silicon substrates by electron beam evaporation method at low substrate temperatures of 250-400 degrees C. The ITO NWs growth was carried out without using an additional reactive oxygen gas and a metal catalyst particle. Ultrafine diameter (similar to 10-15 nm) and micron long ITO NWs growth was observed in a temperature window of 300-400 degrees C. Transmission electron microscope studies confirmed single crystalline nature of the NWs and energy dispersive spectroscopy studies on the NWs confirmed that the NWs growth proceeds via self catalytic vapor-liquid-solid (VLS) growth mechanism. ITO nanowire films grown on glass substrates at a substrate temperature of 300-400 degrees C have shown similar to 2-6% reflection and similar to 70-85% transmission in the visible region. Effect of deposition parameters was systematically investigated. The large area growth of ITO nanowire films would find potential applications in the optoelectronic devices. (C) 2014 Elsevier Ltd. All rights reserved.

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.