$$\hbox {SiO}_{2}\hbox {/TiO}_{2}$$ multi-layered thin films with self-cleaning and enhanced optical properties

Self-cleaning, high transmittance glazing was obtained by cold spray deposition for glazings. The thin films contain \(\hbox {TiO}_{2}\), \(\hbox {SiO}_{2}\) and Au nanoparticles in different structures which allow for tailoring the optical, hydrophilic and photocatalytic properties. The crystallinity, morphology and surface energy were correlated with the optical transmittance and reflectance; the transmittance increased from 89.45 (for the glass substrate) to 91.76% when Au nanoparticles were used in the tandem layered structures. The samples containing alternating multi-layered \(\hbox {SiO}_{2}\) and \(\hbox {TiO}_{2}\) thin films without gold nanoparticles show hydrophilic surface; for these layers, the photocatalytic efficiency reaches 40% under simulated solar radiation. A conditioning effect based on adsorption was observed to increase the photocatalytic efficiency. These highly transparent coatings are well suited for glazings and fenestration, showing the self-cleaning effect based on combined superhydrophilicity and photocatalysis.     

Ga doping induced structural and optical modification in $$\hbox {Ge}_{2}\hbox {Sb}_{2}\hbox {Te}_{5}$$ Ge 2 Sb 2 Te 5 thin films

\(\text {Ge}_2\text {Sb}_2\text {Te}_5\) (GST) is considered a promising candidate for next-generation data storage devices due to its unique property of non-volatility and low power consumption. In present work, the bulk alloys and thin films of (\(\text {Ge}_2\text {Sb}_2\text {Te}_5\))\(_{100-x}\text {Ga}_x\) (x = 0, 3, and 10) are prepared using melt quenching and thermal deposition method, respectively. The effect of Ga doping on host composition is investigated by analyzing X-ray diffraction patterns and field emission scanning electron microscope images. From obtained results, it is found that all doped thin films retained the amorphous nature and exhibited uniform and smooth morphology. In Raman spectra, the appearance of a new peak in 10% Ga-doped GST thin film indicated an alteration in the atomic arrangement of host lattice. Transmission spectra revealed the highly transparent nature of all deposited thin films in the near-infrared region. The optical band gap of Ga-doped GST thin film is lower than that of the pure GST thin film which can be correlated with an increase in band tailing, attributed to an increase in localized defect states in the band gap. Due to the pronounced electronegativity difference between the Ga and Te element, new Ga–Te bonds with a higher number of wrong bonds (Ge–Ge, Sb–Sb, and Ge–Sb) are expected to thermally stabilize the amorphous phase. Such results predict the better performance of Ga-doped GST composition for better performance of phase-change random access memory.

     

Superconducting epitaxial $$\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-\delta }$$ on $$\hbox {SrTiO}_{3}$$SrTiO3-buffered Si(001)

Thin films of optimally doped(001)-oriented \(\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-\updelta }\) are epitaxially integrated on silicon(001) through growth on a single crystalline \(\hbox {SrTiO}_{3}\) buffer. The former is grown using pulsed-laser deposition and the latter is grown on Si using oxide molecular beam epitaxy. The single crystal nature of the \(\hbox {SrTiO}_{3}\) buffer enables high quality \(\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-\updelta }\) films exhibiting high transition temperatures to be integrated on Si. For a 30-nm thick \(\hbox {SrTiO}_{3}\) buffer, 50-nm thick \(\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-\updelta }\) films that exhibit a transition temperature of \(\sim \)93 K, and a narrow transition width (<5 K) are achieved. The integration of single crystalline \(\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-\updelta }\) on Si(001) paves the way for the potential exploration of cuprate materials in a variety of applications.     

Inhomogeneous Superconducting Behaviour in $$\hbox {La}_{5}\hbox {Ni}_{2}\hbox {Si}_{3}$$

The superconducting phase transition at \(T_\mathrm{c} = 2.3\) K was observed for the electrical resistivity \(\rho ({T})\) and magnetic susceptibility \(\chi (T)\) measurements in the ternary compound La\(_{5}\hbox {Ni}_{2}\hbox {Si}_{3}\) that crystallizes in the hexagonal-type structure. Although a single-phase character with the nominal stoichiometry of the synthesized sample was confirmed, a small trace of the La–Ni phase was found, being probably responsible for the superconducting behaviour in the investigated compound. The magnetization loop recorded at \({T} = 0.5\) K resembles a star-like shape which indicates that the density of the critical current can be strongly suppressed by a magnetic field. The low-\(T _{\rho }(T)\) and specific heat \({C}_\mathrm{p}({T})\) data in the normal state reveal simple metallic behaviour. No clear evidence of a phase transition to any long- or short-range order was found for \(C_\mathrm{p}(T)\) measurements in the T-range of 0.4–300 K.     

Effect of Hafnium Impurities on the Magnetoresistance of $$\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-\delta }$$

In the present study, we investigate the influence of the hafnium (Hf) impurities on the magnetoresistance of \(\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-\delta }\) ceramic samples in the temperature interval of the transition to the superconducting state in constant magnetic field up to 12 T. The cause of the appearance of low- temperature “tails” (paracoherent transitions) on the resistive transitions, corresponding to different phase regimes of the vortex matter state is discussed. At temperatures higher than the critical temperature (T > \(T_\mathrm{c})\), the temperature dependence of the excess paraconductivity can be described within the Aslamazov–Larkin theoretical model of the fluctuation conductivity for layered superconductors.     

High-pressure studies of superconductivity in $$\hbox {BiO}_{0.75}\hbox {F}_{0.25}\hbox {BiS}_{2}$$

\(\hbox {BiO}_{0.75}\hbox {F}_{0.25}\hbox {BiS}_{2}\) crystallizes in tetragonal CeOBiS\(_{2}\) structure (S. G. P4/nmm). We have investigated the effect of pressure on magnetization measurements. Our studies suggest improved superconducting properties in polycrystalline samples of \(\hbox {BiO}_{0.75}\hbox {F}_{0.25}\hbox {BiS}_{2}\). The \(T_{\mathrm{c}}\) in our sample is 5.3 K, at ambient pressure, which is marginal but definite enhancement over \(T_{\mathrm{c}}\) reported earlier (= 5.1 K). The upper critical field \(H_{\mathrm{c}2}\)(0) is greater than 3 T, which is higher than earlier report on this material. As determined from the M–H curve, both \(H_{\mathrm{c}2}\) and \(H_{\mathrm{c}1}\) decrease under external pressure P (0 \(\le P \le \) 1 GPa). We observe a decrease in critical current density and transition temperature on applying pressure in \(\hbox {BiO}_{0.75}\hbox {F}_{0.25}\hbox {BiS}_{2}\).     

Characterization and optical properties of $$\hbox {Pr}_{2}\hbox {O}_{3}$$-doped molybdenum lead-borate glasses

\(\hbox {Pr}^{3+}\) doped molybdenum lead-borate glasses with the chemical composition 75PbO?[25–(x \(+\) y)\(\hbox {B}_{2}\hbox {O}_{3}]\)–\(y\hbox {MoO}_{3}\)–\(x\hbox {Pr}_{2}\hbox {O}_{3}\) (where \(x = 0.5\) and 1.0 mol% and \(y = 0\) and 5 mol%) were prepared by conventional melt-quenching technique. Thermal, optical and structural analyses are carried out using DSC, UV and FTIR spectra. The physical parameters, like glass transition \((T_{\mathrm{g}})\), stability factor \((\Delta T)\), optical energy band gap \((E_{\mathrm{gopt}})\), of these glasses have been determined as a function of dopant concentration. The \({T}_{\mathrm{g}}\) and optical energy gaps of these glasses were found to be in the range of 290–350\({^{\circ }}\hbox {C}\) and 2.45–2.7 eV, respectively. Stability of the glass doped with \(\hbox {Pr}^{3+}\) is found to be moderate (\(\sim \)40). The results are discussed using the structural model of Mo–lead-borate glass.     

Radiative Properties of Ceramic $$\hbox {Al}_{2}\hbox {O}_{3}$$, AlN,and $$\hbox {Si}_{3}\hbox {N}_{4}$$Si3N4: I. Experiments

The radiative properties of dense ceramic \(\hbox {Al}_{2}\hbox {O}_{3}\), AlN, and \(\hbox {Si}_{3}\hbox {N}_{4}\) plates are investigated from the visible to the mid-infrared region at room temperature. Each specimen has different surface finishings on different sides of the laminate. A monochromator was used with an integrating sphere to measure the directional-hemispherical reflectance and transmittance of these samples at wavelengths from 0.4 \(\upmu \hbox {m}\) to 1.8 \(\upmu \hbox {m}\). The specular reflectance was obtained by a subtraction technique. A Fourier-transform infrared spectrometer was used to measure the directional-hemispherical or specular reflectance and transmittance with appropriate accessories from about 1.6 \(\upmu \hbox {m}\) to 19 \(\upmu \hbox {m}\). All measurements were performed at near-normal incidence on either the smooth side or the rough side of the sample. The experimental observations are qualitatively interpreted considering the optical constants, surface roughness, and volume scattering and absorption.     

Correlations for the Dielectric Constants of $$\hbox {H}_{2}\hbox {S}$$, $$\hbox {SO}_{2}$$SO2, and $$\hbox {SF}_{6}$$SF6

A new method is developed for correlating the static dielectric constant of polar fluids over wide ranges of conditions where few experimental data exist. Molecular dynamics simulations are used to establish the temperature and density dependence of the Kirkwood g-factor, and also the functional form for the increase of the effective dipole moment with density. Most parameters in the model are obtained entirely from simulation; a single proportionality constant is adjusted to obtain agreement with the limited experimental data. The method is applied to hydrogen sulfide (\(\hbox {H}_{2}\hbox {S}\)) and sulfur dioxide \((\hbox {SO}_{2})\), both of which are important in geochemistry but have only a few dielectric data available. The resulting correlations agree well with the available liquid data, obey physical boundary conditions at low density and at high temperature, and interpolate in density and temperature in a physically reasonable manner. In addition, we present a more conventional correlation for the dielectric constant of sulfur hexafluoride, \(\hbox {SF}_{6}\), where more data are available.     

Effect of annealing treatment on optical properties and microstructural variation of $$\hbox {WO}_{3}/\hbox {Ag}/\hbox {WO}_{3}$$ multilayer nano-films

Structural and optical properties of \(\text {WO}_{3}/\text {Ag}/\text {WO}_{3}\) nano-multilayer composites were investigated for heat mirror applications. \(\text {WO}_{3}/\text {Ag}/\text {WO}_{3}\) thin films were fabricated through a physical vapour deposition method by using electron-beam evaporation at the vacuum chamber at 10\(^{-5}\) Torr. \(\text {WO}_{3}\) nano-layer was fabricated at 40 nm. Annealing treatment was carried out at 100, 200, 300 and 400\(^{\circ }\)C for 1 h after the deposition of first layer of \(\text {WO}_{3}\) on the glass. On \(\text {WO}_{3}\) film, Ag nano-layers with 10, 12 or 14 nm thickness were deposited. Individual layers morphology was investigated using atomic force microscopy (AFM) and deduced that a smoother layer can be achieved after the annealing at 300\(^{\circ }\)C. Ellipsometry analysis was executed to determine both layers, Ag film thickness and inter-diffusion between the \(\text {WO}_{3}\)–Ag–\(\text {WO}_{3}\) layers. It was inferred that there was almost no interfering among the \(\text {WO}_{3}\)–\(\text {WO}_{3 }\) layers in the samples with 12 and 14 nm Ag thickness; while silver was deposited on the annealed \(\text {WO}_{3}\) layer at 300\(^{\circ }\)C. UV–visible spectrophotometer showed that the annealing treatment of the first \(\text {WO}_{3}\) layer enhanced the transparency of films in the visible region. The innovations of the present study have been based on the annealing of the films and finding an optimum thickness for the Ag film at 12–14 nm. Heat mirrors efficiency was assessed according to the principle of their optical behaviour and optimum performance obtained for 14 nm of Ag film, deposited on annealed tungsten oxide at 300\(^{\circ }\)C.     

Synthesis,characterization and electrochemical performance of $$\hbox {Li}_{2}\hbox {Ni}_{x}\hbox {Fe}_{1-x}\hbox {SiO}_{4}$$ cathode materials for lithium ion batteries

\(\hbox {Li}_{2}\hbox {Ni}_{x}\hbox {Fe}_{1-x}\hbox {SiO}_{4}\) (\(x = 0\), 0.2, 0.4, 0.6, 0.8 and 1) samples were prepared by a sol–gel process. The crystal structure of prepared samples of \(\hbox {Li}_{2}\hbox {Ni}_{x}\hbox {Fe}_{1-x}\hbox {SiO}_{4}\) was characterized using an X-ray diffractometer. Different crystallographic parameters such as crystallite size and lattice cell parameters have been calculated. Scanning electron microscopy and Fourier transform infrared spectroscopy investigations were carried out, which reveal the morphology and function groups of the synthesized samples. Furthermore, electrochemical impedance spectra measurements are performed. The obtained results indicated that the highest conductivity is achieved for the \(\hbox {Li}_{2}\hbox {Ni}_{0.4}\hbox {Fe}_{0.6}\hbox {SiO}_{4}\) electrode compound. It was observed that Li–\(\hbox {Li}_{2}\hbox {Ni}_{0.4}\hbox {Fe}_{0.6}\hbox {SiO}_{4}\) battery has initial discharge capacity of 164 mAh \(\hbox {g}^{-1}\) at 0.1C rate. The cycle life performance of all \(\hbox {Li}_{2}\hbox {Ni}_{x}\hbox {Fe}_{1-x}\hbox {SiO}_{4}\) batteries ranged between 100 and 156 mAh \(\hbox {g}^{-1}\) with coulombic efficiency range between 70.9 and 93.9%.     

Thermal Emittance of $$\hbox {La}_{0.7}\hbox {Ca}_{0.3-x}\hbox {K}_x\hbox {MnO}_3$$ Coatings on Aluminum Substrate

A novel thermal control coating was presented based on the thermochromism of manganite. The pigment of K-doped manganite nanoparticles was dispersed into polymer matrix to prepare the coating with curing below 200 \(^{\circ }\)C. The nanoparticles size mainly distributes around 100–200 nm, and it shows a comparable stoichiometric ratio. The phase transition of the nanoparticles was observed from ferromagnetic metallic to paramagnetic insulator state. With increasing K doping level, the phase transition temperature increases, achieving controllable adjustment. Coating surface with and without pore defect was obtained by different polymer matrix. A sharp emittance variation was observed with increasing temperature in K-doped coating. The variation magnitude of emittance is up to 0.46, which is attractive to space thermal control. It is suggested that the pigment content of 50 wt% is sufficient to realize a large emittance variation.     

Structures and electronic properties of $$\hbox {W}_{m}\hbox {Cu}_{n}\,(n + m \le 7)$$ clusters

Geometric and electronic structures of \(\hbox {W}_{m}\hbox {Cu}_{n}\, (m + n \le 7)\) cluster have been systematically calculated by density functional theory at the generalized gradient approximation level for ground-state structures. \(\hbox {W}_{m}\hbox {Cu}_{n}\) clusters with \(n = 1, 3, 5\) tend to form bipyramid structures, whereas \(\hbox {WCu}_{n}\) favour planar shapes except for \(\hbox {WCu}_{5}\). The configurations of \(\hbox {W}_{m}\hbox {Cu}_{n}\) clusters are more sensitive to the Cu atoms than the W atoms, while the average atomic binding energies and the total magnetic moments are determined by W atoms. The calculated second-order differences in energies and HOMO–LOMO energy gaps show pronounced odd–even oscillating behaviours. From the Mulliken electron population analysis, we found that Cu 4p and W 6p orbitals exhibit electronic charges and both Cu 4s and W 6s orbitals transfer electronic charges to the W 5d orbital, which lead to the extension of W–Cu bond lengths.     

Thermally induced cation ordering in $$\hbox {ZnAl}_{2}\hbox {O}_{4}{:}\hbox {Mg}^{2+}$$ ZnAl 2 O 4 : Mg 2 + , $$\hbox {Fe}^{3+}$$ Fe 3 + for sensing thermal history through photoluminescence

Journal of Materials Science - Applicability of spinel compounds is mainly governed by cation distribution in them. In the presented study, thermally induced cation ordering is found to influence...     

Effect of annealing temperature and $$\hbox {CdCl}_{2}$$ treatment on the photo-conversion efficiency of $$\hbox {CdTe/Zn}_{0.1}$$CdTe/Zn0.1$$\hbox {Cd}_{0.9}$$Cd0.9S thin film solar cells

We report the effects of annealing in conjunction with \(\hbox {CdCl}_{2}\) treatment on the photovoltaic properties of \(\hbox {CdTe/Zn}_{0.1}\hbox {Cd}_{0.9}\)S thin film solar cells. CdTe layer is subjected to dry \(\hbox {CdCl}_{2}\) treatment by thermal evaporation method and subsequently, heat treated in air using a tube furnace from 400 to \(500{^{\circ }}\hbox {C}\). AFM and XRD results show improved grain size and crystallographic properties of the CdTe film with dry \(\hbox {CdCl}_{2}\) treatment. This recrystallization and grain growth of the CdTe layer upon \(\hbox {CdCl}_{2}\) treatment translates into improved photo-conversion efficiencies of \(\hbox {CdTe/Zn}_{0.1}\hbox {Cd}_{0.9}\)S cell. The results of dry \(\hbox {CdCl}_{2}\) treatment were compared with conventional wet \(\hbox {CdCl}_{2}\) treatment. Photo-conversion efficiency of 5.2% is achieved for dry \(\hbox {CdCl}_{2}\)-treated cells in comparison with 2.4% of wet-treated cell at heat treatment temperature of \(425{^{\circ }}\hbox {C}\).     

Chemical synthesis and characterization of nano-sized rare-earth ruthenium pyrochlore compounds $$\hbox {Ln}_{2}\hbox {Ru}_{2}\hbox {O}_{7}$$ (Ln = rare earth)

The rare-earth ruthenium pyrochlores \(\hbox {Ln}_{2}\hbox {Ru}_{2}\hbox {O}_{7}\) (\(\hbox {Ln} = \hbox {La}^{3+}\), \(\hbox {Pr}^{3+}\), \(\hbox {Nd}^{3+}\), \(\hbox {Sm}^{3+}\) and \(\hbox {Gd}^{3+}\)) have been synthesized by the tartrate co-precipitation method, which allowed control of their composition and morphology. The preparation processes were monitored by thermal studies (TG-DTA). The obtained ruthenates were characterized by X-ray diffraction (XRD), TEM, d.c. electrical conductivity, thermoelectric power and dielectric constant measurements. X-ray diffraction patterns for all pyrochlore samples indicate a single-phase crystalline material with a cubic structure except for \(\hbox {LaRuO}_{3}\), which shows perovskite orthorhombic structure. The structural parameter for the solid obtained was successfully determined by Rietveld refinement based on the analysis of powder XRD pattern. The TEM photographs of these compounds exhibited the average particle size in the range of 36.4–73.8 nm. The data on the temperature variation of d.c. electrical conductivity showed that all rare-earth ruthanates are semiconductors and major carriers are electrons. The conduction mechanism of these compounds seems to be oxygen non-stoichiometry. The variation of dielectric constant at various frequencies showed initially interfacial polarization up to 275 kHz and beyond, which shows domain wall motion.     

Influence of the conditions of a solid-state synthesis anode material $$\hbox {Li}_{4}\hbox {Ti}_{5}\hbox {O}_{12 }$$ on its electrochemical properties of lithium cells

Lithium–titanium spinel is a promising electrode material for high power and environmentally friendly batteries. We did research on \(\hbox {Li}_{4}\hbox {Ti}_{5}\hbox {O}_{12 }\) (LTO) samples, which were synthesized via solid-state reaction at various conditions in a temperature range from 800 to \(900{^{\circ }}\hbox {C}\) and they were investigated by XRD, SEM, IS, cyclic voltammetry and the galvanostatic charge–discharge tests. X-ray diffractions show that all of the samples have a spinel structure with Fd-3m space group with a small amount of impurities \(\hbox {TiO}_{2}\) (anatase). Lithium ion batteries with LTO-based electrode exhibit excellent reversible capacity of \(\,\sim 180\hbox { mAh}\hbox { g}^{-1}\) in the current density range from 0.1 to 1 C. As an electrode material for rechargeable lithium-ion batteries, LTO-F demonstrates the best rate and cyclic performance from all of the studied samples.     

$$\hbox {RuO}_{2}$$ Non-isothermal Thermometry

The use of a \(\hbox {RuO}_{2}\) resistor in non-isothermal measuring setup is proposed. A calculation is presented to explain the principle for a resistor obeying variable-range-hopping theory and the results are compared to measurements in the range of 11.2–30 mK for a commercial resistor. The thermometer, which measures the electron temperature, does not show overheating effects at 11.2 mK with a measuring power of \(10^{-12}\) W.