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.     

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.     

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.     

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...     

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.     

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

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.     

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.     

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%.     

Formation of $$\hbox {Mg}_{2}\hbox {C}_{3}$$ phase in N220 nanocarbon containing low carbon MgO-C composition

This paper reports a non-conventional microstructure with sequicarbide \((\hbox {Mg}_{2}\hbox {C}_{3})\) formation in N220 nanocarbon containing low carbon magnesia carbon composition having magnesium metal powder as antioxidant. 5 wt% graphite containing MgO-C refractory with and without 1 wt% N220 nanocarbon is studied and 2 wt% magnesium metal powder is used as the lone antioxidant. The compositions were mixed with powder and liquid resin binder, pressed uniaxially at 150 MPa and cured at 220\(^{\circ }\hbox {C}\). Cured samples were coked at 1000\(^{\circ }\hbox {C}\) for 2 h. Matrix of the coked samples was studied in detail for microstructural analysis phase content and formation of nail-shaped sequicarbide was found in the nanocarbon containing compositions. The in-situ sequicarbide formation has resulted in the strength of the batch.     

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.     

Microwave-hydrothermal synthesis of mesoporous $$\upgamma $$-$$\hbox {Al}_{2}\hbox {O}_{3}$$Al2O3 and its impregnation with AgNPs for excellent catalytic oxidation of CO

Mesoporous \(\upgamma \)-alumina was synthesized by the microwave-hydrothermal process with a shorter duration time at 150\({^{\circ }}\)C/2 h followed by calcination at 550\({^{\circ }}\)C/1 h. Ag nanoparticles (AgNPs) were impregnated into \(\upgamma \)-alumina under a reducing atmosphere at 450\({^{\circ }}\)C. The synthesized product was characterized by X-ray diffraction (XRD), thermogravimetric (TG)/differential thermal analysis (DTA), X-ray photoelectron spectroscopy (XPS), \(\hbox {N}_{2}\) adsorption–desorption study, field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The BET surface area values of \(\upgamma \)-alumina and Ag-impregnated \(\upgamma \)-alumina were found to be 258 and 230 m\(^{2}\) g\(^{-1}\), respectively. FESEM images showed the formation of grain-like particles of 50–70 nm in size with a flake-like microstructure. The XRD, XPS and TEM studies confirmed the presence of Ag in the synthesized product. Catalytic properties of the product for CO oxidation was studied with the \(T_{50}\) (50% conversion) and \(T_{100}\) (100% conversion) values of 118 and 135\({^{\circ }}\)C, respectively; the enhanced values were compared with the literature reported values.     

Electro-optical properties,decomposition pathways and the hydrostatic pressure-dependent behaviours of a double-cation hydrogen storage material of $$\hbox {Al}_{3}\hbox {Li}_{4}(\hbox {BH}_{4})_{13}$$

Electro-optical properties, the decomposition pathways and the pressure-dependent behaviours of \(\hbox {Al}_{3}\hbox {Li}_{4}(\hbox {BH}_{4})_{13}\) have been investigated using a first-principle plane-wave pseudopotential method. \(\hbox {Al}_{3}\hbox {Li}_{4}(\hbox {BH}_{4})_{13}\) is a kind of double-cation borohydride, consisting of distorted tetrahedral anions \([\hbox {Al}(\hbox {BH}_{4})_{4}]^{-}\) and cations \([\hbox {Li}_{4}(\hbox {BH}_{4})]^{3+}\), which obeys the stability criteria of decomposition reactions. Herein, two possible decomposition reactions of the compound are proposed, which release 18 hydrogen molecules (about 12.03 wt%) in the first reaction and 24 hydrogen molecules (about 16.04 wt%) in the second reaction. On increasing the pressure on the structure, the lattice parameter, the volume of unit cell, the quasiparticle band gap and also enthalpy of the system decrease nearly monotonically; therefore, the acceptor levels gradually get filled and the Fermi level shifts upward. Results of computational investigations of the structural, electronic and thermodynamic parameters and their pressure-dependent behaviours indicate that \(\hbox {Al}_{3}\hbox {Li}_{4}(\hbox {BH}_{4})_{13}\) has intriguing properties. Therefore, it would be a very promising material for hydrogen storage technology.     

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.

     

Synthesis and enhanced photocatalytic activity of g-$$\hbox {C}_{3}\mathrm{N}_{4}$$ hybridized CdS nanoparticles

The highly effective g-\(\hbox {C}_{3}\hbox {N}_{4}\) hybridized CdS photocatalysts were synthesized via a successive calcination and hydrothermal process. The as-prepared photocatalysts were characterized by X-ray powder diffraction, transmission electron microscopy and UV–Vis diffuse reflectance spectroscopy. The photocatalytic performance of the \(\hbox {C}_{3}\hbox {N}_{4}\)/CdS nanocomposites was evaluated by the photodegradation of RhB under visible light irradiation. The results showed that photocatalytic ability of the \(\hbox {C}_{3}\hbox {N}_{4}\)/CdS nanocomposites was higher than that of pure \(\hbox {C}_{3}\hbox {N}_{4}\) and CdS. The enhanced photocatalytic activity could be attributed to the high separation efficiency of the photo-excited electron-hole pairs. A possible mechanism of the photocatalytic degradation of RhB on \(\hbox {C}_{3}\hbox {N}_{4}/\)CdS nanocomposites was also proposed.     

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

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.