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.     

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.     

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.     

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.     

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

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.     

$$\hbox {RuO}_{2}$$ 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.     

Application of Non-Isothermal Thermogravimetric Method to Interpret the Decomposition Kinetics of \hbox {NaNO}_{3}, \hbox {KNO}_{3}, and \hbox {KClO}_{4}

The non-isothermal thermogravimetric method was used to study the thermal decomposition of \(\hbox {KClO}_{4}, \hbox {KNO}_{3}\) , and \(\hbox {NaNO}_{3}\) at heating rates of (5, 10, 15, and 20)  \(\hbox {K}\cdot \hbox {min}^{-1}\) . The activation energy of thermal decomposition reactions was computed by isoconversional methods of Ozawa–Flynn–Wall, Kissinger–Akahiro–Sunose, and Friedman equations. Also, the kinetic triplet of the thermal decomposition of salts was determined by the model-fitting method of the modified Coats–Redfern equation. The activation energies of \(\hbox {KClO}_{4}, \hbox {KNO}_{3}\) , and \(\hbox {NaNO}_{3}\) of (293 to 307, 160 to 209, and 192 to 245)  \(\hbox {kJ}\cdot \hbox {mol}^{-1}\) , respectively, are obtained by non–isothermal isoconversional methods. The modified Coats and Redfern method showed that the most probable mechanism functions \(g(\alpha )\) of \([-\hbox {ln}(1 - \alpha )]^{1/3}\) (model A3: Arami–Erofeev equation) and \((1 - \alpha )^{-1}- 1\) (model F2: second order) can be used to predict the decomposition mechanisms of \(\hbox {KClO}_{4}\) , \(\hbox {KNO}_{3}\) , and \(\hbox {NaNO}_{3}\) , respectively.     

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.     

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).     

Evolution of the electrical resistance of \bf{\hbox {YBa}_2\hbox {Cu}_3\hbox {O}_{7-\varvec\delta }} single crystals in the course of long-term aging

Investigated are the changes in the basal-plane electrical resistivity of an optimally doped \(\hbox {YBa}_2\hbox {Cu}_3\hbox {O}_{7-\delta }\) single crystal in the course of long-term aging (17 years) at room temperature in air. In consequence of aging the sample has decomposed into three phases with different temperatures of the superconducting transition, while the transition widths of these phases have increased significantly. The temperature dependence of the electrical resistivity has retained a metallic character. The fluctuation conductivity near the critical temperature is described well by the 3D Aslamazov–Larkin model. In the course of aging significant changes in the scattering characteristics have been observed, whereas the Debye temperature has changed slightly and the transverse coherence length has remained constant.     

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.     

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.