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.     

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.     

$$\hbox {RuO}_{2}$$ 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.     

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.     

$$\hbox {SiO}_{2}\hbox {/TiO}_{2}$$ 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.     

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.     

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 \(\hbox {BiO}_{0.75}\hbox {F}_{0.25}\hbox {BiS}_{2}\).     

Distribution of relaxation times investigation of $$\hbox {Co}^{3+}$$ doping lithium-rich cathode material $$\hbox {Li}[\hbox {Li}_{0.2} \hbox {Ni}_{0.1} \hbox {Mn}_{0.5} \hbox {Co}_{0.2}]\hbox {O}_{2}$$Li[Li0.2Ni0.1Mn0.5Co0.2]O2

The element \(\hbox {Co}^{3+}\) was introduced into lithium-rich material \(0.5\hbox {Li}_{2}\hbox {MnO}_{3} \cdot 0.5 \hbox {LiNi}_{0.5}\hbox {Mn}_{0.5}\hbox {O}_{2}\) by a polyacrylamide-assisted sol–gel method to form \(\hbox {Li}[\hbox {Li}_{0.2} \hbox {Ni}_{0.1} \hbox {Mn}_{0.5} \hbox {Co}_{0.2}]\hbox {O}_{2}\) and better electro-chemical performances were observed. Electrochemical impedance spectroscopy spectra were measured on 11 specific open circuit voltage levels on the initial charge profile. Then they were converted to the distribution of relaxation times (DRTs) g(\(\tau \)) by self-consistent Tikhonov regularization method. The obtained DRTs offered a higher resolution in the frequency domain and provided the number and the physical origins of loss processes clearly. Through the analysis of DRTs, the rapid augmentation of resistance to electronic conduction and charge transfer within the voltage range 4.46–4.7 V where the removal of \(\hbox {Li}_{2}\hbox {O}\) from \(\hbox {Li}_{2} \hbox {MnO}_{3}\) component took place was the most remarkable phenomenon and the \(\hbox {Co}^{3+}\) doping greatly reduced the resistance to electronic conduction Re. This gave us more evidence about the complicated ‘structurally integrated’ composite character of the material.     

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.     

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.     

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 \(425{^{\circ }}\hbox {C}\).     

Dielectric properties study of surface engineered nano$$\hbox {TiO}_{2}$$/epoxy composites

Nanodielectrics are promising materials that can efficiently store a large amount of electrical energy that are desirable for many electronic and power devices. Control of polymer–particle interface in nanodielectrics is very critical in not only obtaining the improved quality of dispersion but also in altering the dielectric properties. Various surface modifying agents with linear (alkyl), aromatic (phenyl) and extended aromatic (naphthyl) chemical nature were employed at the epoxy–nano\(\hbox {TiO}_{2}\) interface. All the surface-modifying agents were successful in passivating the nanoparticles surface and in obtaining the improved quality of polymer–particle dispersion and improved glass transition temperature comparatively. However, all the surface modifiers were not successful in obtaining the improved dielectric properties of the nanodielectrics, especially dielectric breakdown resistance. Only the extended aromatic group at the polymer–particle interface, which is more electron withdrawing in electronic nature than phenyl and alkyl structures, was successful in improving the dielectric breakdown resistance. Thus, the choice of surface-modifying agent based on its chemical and electronic nature is very important in optimizing the dielectric properties of nanodielectrics. Naphthyl phosphate-modified nano\(\hbox {TiO}_{2}\)–epoxy composite films of \(\sim \)90–100 \(\upmu \)m thick at 5 vol% particle concentration yielded higher dielectric breakdown resistance than pure epoxy polymer and thereby resulted in about 90% higher electrical energy storage density than the pure epoxy film.     

Microwave hydrothermal synthesis and upconversion luminescence properties of $$\hbox {Yb}^{3+}$$/$$\hbox {Tm}^{3+}$$Tm3+ co-doped $$\hbox {NaY}(\hbox {MoO}_{4})_{2}$$NaY(MoO4)2 phosphor

Tetragonal \(\text {NaY}(\text {MoO}_{4})_{2}\) (NYM) phosphors co-doped with \(\hbox {Yb}^{3+}\) and \(\hbox {Tm}^{3+}\) ions were synthesized through microwave hydrothermal method followed by calcining treatment. Powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and photoluminescence spectra were used to characterize the properties of as-prepared samples. The results show that \(\hbox {Yb}^{3+}\)/\(\hbox {Tm}^{3+}\) co-doped NYM displayed bright blue emission near 472 and 476 nm (\(^{1}\hbox {G}_{4}\rightarrow {}^{3}\hbox {H}_{6}\) transition), strong near-infrared upconversion (UC) emission around 795 nm (\(^{3}\hbox {H}_{4}\rightarrow {}^{3}\hbox {H}_{6}\) transition). The optimum doping concentrations of \(\hbox {Yb}^{3+}\) and \(\hbox {Tm}^{3+}\) for the most intense UC luminescence were obtained, and the related UC mechanism of \(\hbox {Yb}^{3+}\)/\(\hbox {Tm}^{3+}\) co-doped NYM depending on pump power was studied in detail.     

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.     

Interface engineering of $$\hbox {TiO}_{2}$$@PANI nanostructures for efficient visible-light activation

Core–shell-structured \(\hbox {TiO}_{2}\)@PANI composites were fabricated using negatively charged titanium glycolate (TG) precursor spheres, which were decorated using hydrochloric acid; subsequently, the uniform polyaniline (PANI) layer could be attached onto the surface of the polystyrene spheres by in situ chemical oxidative polymerization and finally, the resulting PANI-grafted TG were allowed to hydrolyse by treating the material with hot water. The TGs were transformed to porous \(\hbox {TiO}_{2}\), leading to the formation of core–shell \(\hbox {TiO}_{2}\)@PANI composites. The resulting \(\hbox {TiO}_{2}\)@PANI composite photocatalysts were characterized by X-ray diffraction, scanning electron microscopy, ultraviolet–visible diffuse reflection spectroscopy and photoluminescence spectroscopy. Significantly, the \(\hbox {TiO}_{2}\)@PANI composite photocatalysts exhibited dramatically enhanced photo-induced electron–hole separation efficiency, which was confirmed by the results of photocurrent measurements. PANI was dispersed uniformly over the porous \(\hbox {TiO}_{2}\) surface with an intimate electronic contact on the interface to act cooperatively to achieve enhanced photocatalytic properties, indicating that core–shell \(\hbox {TiO}_{2}\)@PANI composite photocatalysts could be promising candidate catalysts under visible-light irradiation. The mechanism of enhancing photocatalytic activity was proposed on the basis of the experimental results and estimated energy band positions.     

Milling effect on the photo-activated properties of $$\hbox {TiO}_{2}$$ nanoparticles: electronic and structural investigations

Commercial PC105 titanium dioxide nanoparticles were studied under mechanical milling process. The effect of milling time and speed on the structural and electronic properties of \(\hbox {TiO}_{2}\) powder was then investigated using X-ray powder diffraction (XRD), dynamic light scattering (DLS), transmission electronic microscopy (TEM), electron paramagnetic resonance (EPR) and UV–visible spectroscopy. The related photo-catalytic properties of the milled nanoparticles were probed following the degradation rate of methylene orange (MO) under UV-light irradiation and through EPR spin-scavenging approach. Comparison with pristine powder shows that milled nanoparticles are significantly less reactive upon illumination, despite decreased radius and hence, higher specific area. Such low yield of reactive species is attributed to the apparition of the amorphous \(\hbox {TiO}_{2}\) and brookite phase upon milling, as well as increased charge carrier recombination as pointed out by the presence of sacrificial electron donor.     

Molecular Dynamics Study of Surface Anisotropy in $$\hbox {Ag}_{60}\; \hbox {Cu}_{40}$$ Alloy at Nanoscale

In the present study, molecular dynamics simulation has been performed to investigate the anisotropic behavior of free standing \(\hbox {Ag}_{60}\; \hbox {Cu}_{40}\) nanorods. We choose different orientations with various cross sections to study the dynamics of thermal behavior of \(\hbox {Ag}_{60}\; \hbox {Cu}_{40}\) nanorods. The system is modeled using embedded atom method potentials. The radial distribution functions are analyzed to reveal the dynamic evolution of the structural behavior of nanorods with different orientations and sample sizes. The total energy and mean square displacement is also calculated to characterize the melting phenomenon of various samples. The melting temperature of the nanorods is found to be significantly size and orientation dependent, and it increases with the increase in cross-sectional area. The nanorods with low-index crystallographic surfaces such as (110) exhibit lowest melting temperature as compared to compact surfaces (111).     

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.

     

Fabrication and enhanced photoluminescence properties of $$\hbox {NaLa}(\hbox {MoO}_{4})_{2}$$: $$\hbox {Sm}^{3+}$$Sm3+, $$\hbox {Bi}^{3+}$$Bi3+ phosphors with high efficiency white-light-emitting

The tetragonal scheelite-type \(\hbox {Sm}^{3+}\hbox {/Bi}^{3+}\) ions co-doped with \(\hbox {NaLa}(\hbox {MoO}_{4})_{2}\) phosphors were synthesized by a facile sol–gel and combustion process using citric acid as complexing agent. The crystal structure and morphology of these as-prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Furthermore, UV-absorption and the photoluminescence (PL) properties of these phosphors were systematically investigated and the PL of the phosphors shows strong white light emissions. Efficient energy transfer from the \(\hbox {MoO}_{4}^{2-}\) group or \(\hbox {Bi}^{3+}\) ions to \(\hbox {Sm}^{3+}\) ions was established by PL investigation excited at 405 nm. The PL intensity of the studied materials was investigated as a function of different \(\hbox {Sm}^{3+}\) and \(\hbox {Bi}^{3+}\) concentrations. The PL investigations revealed that the phosphors exhibit apparent characteristic emissions, which is ascribed to the transition from the ground state energy level \(^{4}\hbox {G}_{5/2}\) to excited state energy levels \(^{6}\hbox {H}_{\mathrm{J}}\) (\(J= 5/2, 7/2, 9/2\)) and the \(\hbox {NaLa}(\hbox {MoO}_{4})_{2}\): 4 mol% \(\hbox {Sm}^{3+}\) and \(\hbox {NaLa}(\hbox {MoO}_{4})_{2}\): 4 mol% \(\hbox {Sm}^{3+}\), 8 mol% \(\hbox {Bi}^{3+}\) present white emissions with the CIE coordinates of (0.350, 0.285) and (0.285, 0.229), respectively. The absolute quantum efficiencies of the phosphors are 40% (\(\hbox {NaLa}(\hbox {MoO}_{4})_{2}\): 4 mol% \(\hbox {Sm}^{3+}\)) and 52% (\(\hbox {NaLa}(\hbox {MoO}_{4})_{2}\): 4 mol% \(\hbox {Sm}^{3+}\), 8 mol% \(\hbox {Bi}^{3+}\)), respectively.