The Effect of Inhomogeneous Phase on the Critical Temperature of Smart Meta-superconductor MgB<Subscript>2</Subscript>

The critical temperature (T_C) of MgB₂, one of the key factors limiting its application, is highly desired to be improved. On the basis of the meta-material structure, we prepared a smart meta-superconductor structure consisting of MgB₂ micro-particles and inhomogeneous phases by an ex situ process. The effect of inhomogeneous phase on the T_C of smart meta-superconductor MgB₂ was investigated. Results showed that the onset temperature (\(T_{\mathrm {C}}^{\text {on}}\)) of doping samples was lower than those of pure MgB₂. However, the offset temperature (\({T}_{\mathrm {C}}^{\text {off}}\)) of the sample doped with Y₂O₃:Eu³⁺ nanosheets with a thickness of 2 ～ 3 nm which is much less than the coherence length of MgB₂ is 1.2 K higher than that of pure MgB₂. The effect of the applied electric field on the T_C of the sample was also studied. Results indicated that with the increase of current, \({T}_{\mathrm {C}}^{\text {on}}\) is slightly increased in the samples doping with different inhomogeneous phases. With increasing current, the \({T}_{\mathrm {C}}^{\text {off}}\) of the samples doped with nonluminous inhomogeneous phases was decreased. However, the \({T}_{\mathrm {C}}^{\text {off}}\) of the luminescent inhomogeneous phase doping samples increased and then decreased with increasing current.     

Network structure dependence on unconstrained isothermal-recovery processes for shape-memory thiol-epoxy “click” systems

The shape-memory response (SMR) of “click” thiol-epoxy polymers produced using latent catalysts, with different network structure and thermo-mechanical properties, was tested on unconstrained shape-recovery processes under isothermal conditions. Experiments at several programming temperatures (\(T_{\mathrm{prog}}\)) and isothermal-recovery temperatures (\(T_{\mathrm{iso}}\)) were carried out, and the shape-memory stability was analyzed through various consecutive shape-memory cycles. The temperature profile during the isothermal-recovery experiments was monitored, and it showed that the shape-recovery process takes place while the sample is becoming thermally stable and before stable isothermal temperature conditions are eventually reached. The shape-recovery process takes place in two different stages regardless of \(T_{\mathrm{iso}}\): a slow initial stage until the process is triggered at a temperature strongly related with the beginning of network relaxation, followed by the typical exponential decay of the relaxation processes until completion at a temperature below or very close to \(T_{\mathrm{g}}\). The shape-recovery process is slower in materials with more densely crosslinked and hindered network structures. The shape-recovery time (\(t_{\mathrm{sr}}\)) is significantly reduced when the isothermal-recovery temperature \(T_{\mathrm{iso}}\) increases from below to above \(T_{\mathrm{g}}\) because the network relaxation dynamics accelerates. However, the temperature range from the beginning to the end of the recovery process is hardly affected by \(T_{\mathrm{iso}}\); at higher \(T_{\mathrm{iso}}\) it is only slightly shifted to higher temperatures. These results suggest that the shape-recovery process can be controlled by changing the network structure and working at \(T_{\mathrm{iso}} < T_{\mathrm{g}}\) to maximize the effect of the structure and/or by increasing \(T_{\mathrm{iso}}\) to minimize the effect but increasing the shape-recovery rate.     

Microstructure and Magnetic Properties of Sn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> Thin Films Prepared by Flash Evaporation Technique

An effort was made to develop semiconductor oxide-based room temperature dilute magnetic semiconductor (DMS) thin films based on wide band gap and transparent host lattice with transition metal substitution. The Sn\(_{\mathrm {1}-x}\)Ni\(_{x}\textit {O}_{\mathrm {2}}\) (\(x\,= \mathrm {0.00, 0.03, 0.05, 0.07, 0.10, and \,0.15}\)) thin film samples were prepared on glass substrates by flash evaporation technique. All the samples were shown single phase crystalline rutile structure of host SnO\(_{\mathrm {2}}\) with dominant (110) orientation. The Ni substitution promotes reduction of average crystallite size in SnO\(_{\mathrm {2}}\) as evidenced from the reduction of crystallite size from 40 (SnO\(_{\mathrm {2}}\)) to 20 nm (Sn\(_{\mathrm {0.85}}\)Ni\(_{\mathrm {0.15}}\textit {O}_{\mathrm {2}}\)). In the energy dispersive spectra as well as X-ray photoelectron spectra of all the samples show, the chemical compositions are close to stoichiometric with noticeable oxygen deficiency. The crystalline films were formed by coalescence of oval-shaped polycrystalline particles of 100 nm size as evidenced from the electron micrographs. The energy band gap of DMS films decreases from 4 (SnO\(_{\mathrm {2}}\)) to 3.8 eV (x \(=\) 0.05) with increase of Ni content. The magnetic hysteresis loops of all the samples at room temperature show soft ferromagnetic nature except for SnO\(_{\mathrm {2}}\) film. The SnO\(_{\mathrm {2}}\) films show diamagnetic nature and it converts into ferromagnetic upon substitution of 3 % Sn\(^{\mathrm {4+}}\) by Ni\(^{\mathrm {2+}}\). The robust intrinsic ferromagnetism (saturation magnetization, 21 emu/cm\(^{\mathrm {3}}\)). Further increase of Ni content weakens ferromagnetic strength due to Ni-O antiferromagnetic interactions among the nearest neighbour Ni ions via O\(^{\mathrm {2-}}\) ions. The observed magnetic properties were best described by bound magnetic polarons model.     

Electrochemical impedance studies of capacity fading of electrodeposited ZnO conversion anodes in Li-ion battery

Electrodeposited ZnO coatings suffer severe capacity fading when used as conversion anodes in sealed Li cells. Capacity fading is attributed to (i) the large charge transfer resistance, \(R_{\mathrm{ct}}\) (300–700 \(\Omega \)) and (ii) the low \(\hbox {Li}^{+}\) ion diffusion coefficient, \(D_{\mathrm{Li}}^{+}\ (10^{-15}\) to \(10^{-13}\hbox { cm}^{2}\hbox { s}^{-1})\). The measured value of \(R_{\mathrm{ct}}\) is nearly 10 times higher and \(D_{\mathrm{Li}}^{+}\) 10–100 times lower than the corresponding values for \(\hbox {Cu}_{2}\hbox {O}\), which delivers a stable reversible capacity.     

Measurement Uncertainty Budget of the PMV Thermal Comfort Equation

Fanger’s predicted mean vote (PMV) equation is the result of the combined quantitative effects of the air temperature, mean radiant temperature, air velocity, humidity activity level and clothing thermal resistance. PMV is a mathematical model of thermal comfort which was developed by Fanger. The uncertainty budget of the PMV equation was developed according to GUM in this study. An example is given for the uncertainty model of PMV in the exemplification section of the study. Sensitivity coefficients were derived from the PMV equation. Uncertainty budgets can be seen in the tables. A mathematical model of the sensitivity coefficients of \(T_{\mathrm{a}}\), \(h_{\mathrm{c}}\), \(T_{\mathrm{mrt}}\), \(T_{\mathrm{cl}}\), and \(P_{\mathrm{a}}\) is given in this study. And the uncertainty budgets for \(h_{\mathrm{c}}\), \(T_{\mathrm{cl}}\), and \(P_{\mathrm{a}}\) are given in this study.     

Thermodynamic Properties at Saturation Derived from Experimental Two-Phase Isochoric Heat Capacity of 1-Hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide

New measurements are reported for the isochoric heat capacity of the ionic liquid substance 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C6mim][NTf2]). These measurements extend the ranges of our earlier study (Polikhronidi et al. in Phys Chem Liq 52:657, 2014) by 5 % of the compressed liquid density and by 75 K. An adiabatic calorimeter was used to measure one-phase \((C_{\mathrm{V1}})\) liquid and two-phase \((C_{\mathrm{V2}})\) liquid + vapor isochoric heat capacities, densities \((\rho _s)\), and phase-transition temperatures \((T_s)\) of the ionic liquid (IL) substance. The combined expanded uncertainty of the density \(\rho \) and isochoric heat capacity \(C_\mathrm{V}\) measurements at the 95 % confidence level with a coverage factor of \(k = 2\) is estimated to be 0.15 % and 3 %, respectively. Measurements are concentrated in the immediate vicinity of the liquid + vapor phase-transition curve, in order to closely observe phase transitions. The present measurements and those of our earlier study are analyzed together and are presented in terms of thermodynamic properties \((T_s\), \(\rho _s\), \(C_{\mathrm{V1}}\) and \(C_{\mathrm{V2}})\) evaluated at saturation and in terms of key-derived thermodynamic properties \(C_\mathrm{P}\), \(C_\mathrm{S}\), \(W_\mathrm{S}^{{\prime }}\), \(K_{\mathrm{TS}}^{{\prime }}\), \(\left( {\partial P/\partial T} \right) _{\mathrm{V}}^{\prime }\), and \(\left( {\partial V/\partial T} \right) _\mathbf{P}^{\prime })\) on the liquid + vapor phase-transition curve. A thermodynamic relation by Yang and Yang is used to confirm the internal consistency of measured two-phase heat capacities \(C_{\mathrm{V2}} \), which are observed to fall perfectly on a line as a function of specific volume at a constant temperature. The observed linear behavior is exploited to evaluate contributions to the quantity \(C_{\mathrm{V2}} = f(V, T)\) from chemical potential \(C_{{\mathrm{V}\upmu }} =-T\frac{\mathrm{d}^{{2}}\mu }{\mathrm{d}T^{2}}\) and from vapor pressure \(C_{\mathrm{VP}} =VT\frac{\mathrm{d}^{2}P_{\mathrm{S}} }{\mathrm{d}T^{2}}\). The physical nature and specific details of the temperature and specific volume dependence of the two-phase isochoric heat capacity and some features of the other derived thermodynamic properties of IL at liquid saturation curve are considered in detail.     

Mesoscale evolution of non-graphitizing pyrolytic carbon in aligned carbon nanotube carbon matrix nanocomposites

Polymer-derived pyrolytic carbons (PyCs) are highly desirable building blocks for high-strength low-density ceramic meta-materials, and reinforcement with nanofibers is of interest to address brittleness and tailor multi-functional properties. The properties of carbon nanotubes (CNTs) make them leading candidates for nanocomposite reinforcement, but how CNT confinement influences the structural evolution of the PyC matrix is unknown. Here, the influence of aligned CNT proximity interactions on nano- and mesoscale structural evolution of phenol-formaldehyde-derived PyCs is established as a function of pyrolysis temperature (\(T_{\mathrm {p}}\)) using X-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy. Aligned CNT PyC matrix nanocomposites are found to evolve faster at the mesoscale by plateauing in crystallite size at \(T_{\mathrm {p}}\) \(\sim\)800 \(^{\circ }\hbox {C}\), which is more than \(200\,\,^{\circ }\hbox {C}\) below that of unconfined PyCs. Since the aligned CNTs used here exhibit \(\sim\)80 nm average separations and \(\sim\)8 nm diameters, confinement effects are surprisingly not found to influence PyC structure on the atomic-scale at \(T_{\mathrm {p}}\) \(\le \)1400 \(^{\circ }\hbox {C}\). Since CNT confinement could lead to anisotropic crystallite growth in PyCs synthesized below \(\sim\)1000 \(^{\circ }\hbox {C}\), and recent modeling indicates that more slender crystallites increase PyC hardness, these results inform fabrication of PyC-based meta-materials with unrivaled specific mechanical properties.     

Synthesis,structural and dielectric properties of 0.8PMN–0.2PT relaxor ferroelectric ceramic

A 0.8PMN–0.2PT solid-solution ceramic was synthesized by columbite processing technique. The effects of sintering temperature on the density, structure and microstructure and in turn on the dielectric properties were investigated. The ceramics sintered at and above 1050\(^{\circ }\hbox {C}\) resulted in single-phase perovskite formation. However, high density >90% is achieved only after 1170\(^{\circ }\hbox {C}\). Microstructural analysis revealed that grain size increases with increase in sintering temperature. A significant increase in the peak of dielectric permittivity only after 1150\(^{\circ }\hbox {C}\) owing to increase in density is noted in this study. The quadratic law applied to this ceramic demonstrates that the transition is diffused. The broadness in phase transition and lower dielectric relaxation obtained for the composition demonstrate that the ceramic exhibits characteristics of both relaxor and normal ferroelectrics. The ceramic of composition 0.8PMN–0.2PT exhibits excellent dielectric properties \(\varepsilon _{\mathrm{r}\text {-}\mathrm{max}} =\) 20294?27338 at 100 Hz with \(T_{\mathrm{c}} = 100\)–\(96^{\circ }\hbox {C}\) at low sintering temperature 1170–1180\(^{\circ }\hbox {C}\), respectively.     

Effect of Zr Addition on Bi<Subscript>1.8</Subscript>Pb<Subscript>0.4</Subscript>Sr<Subscript>2.0</Subscript>Ca<Subscript>1.1</Subscript>Cu<Subscript>2.1</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Superconductor

The polycrystalline Bi_1.8Pb_0.4Sr_2.0Ca_1.1Cu_2.1 M_xO _y , with M = Zr (x = 0.0, 0.02, 0.04), were synthesized by solid-state reaction method and studied by X-ray diffraction analysis (XRD), scanning electron microscopy equipped with energy dispersive of X-ray analysis (SEM/EDX) and resistivity versus temperature measurements. The influence of the Zr addition on the Tc and microstructure properties of the superconducting compounds has been studied. SEM observations show whiskers grains randomly distributed and microstructural change due to the addition of Zr. The ZrO₂ was incorporated into the crystalline structure of BSCCO system in all samples. The crystallographic structure remains in a tetragonal form where a= b≠c. Generally, all samples exhibit semiconductor behaviour above \(T_{\mathrm {c}}^{\text {onset}}\). The onset critical temperature \(T_{\mathrm {c}}^{\text {onset}}\) increases up to 86 with x = 0.02. There is an enhancement in the critical temperature for doped samples as compared with pure Bi_1.8Pb_0.4Sr_2.0Ca_1.1Cu_2.1O _y .Changes in superconducting properties of ZrO₂ nanoparticle added Bi-2212 system were discussed.     

Electrical and Thermal Characteristics of the Insulator–Metal Transition in Crystalline $$\hbox {V}_{2}\hbox {O}_{5}$$ Films

The electrical and thermal properties with respect to the crystallization in \(\hbox {V}_{2}\hbox {O}_{5}\) thin films were investigated by measuring the resistance at different temperatures and applied voltages. The changes in the crystal structure of the films at different temperatures were also explored using Raman measurements. The thermal diffusivity of the crystalline \(\hbox {V}_{2}\hbox {O}_{5}\) film was measured by the nanosecond thermoreflectance method. The microstructures of amorphous and crystalline \(\hbox {V}_{2}\hbox {O}_{5}\) were observed by SEM and XRD measurements. The temperature-dependent Raman spectra revealed that a structural phase transition does not occur in the crystalline film. The resistance measurements of an amorphous film indicated semiconducting behavior, whereas the resistance of the crystalline film revealed a substantial change near \(250\,{^{\circ }}\hbox {C}\), and Ohmic behavior was observed above \(380\,{^{\circ }}\hbox {C}\). This result was due to the metal–insulator transition induced by lattice distortion in the crystalline film, for which \(T_{\mathrm{c}}\) was \(260\,{^{\circ }}\hbox {C}\). \(T_{\mathrm{c}}\) of the film decreased from 260 \({^{\circ }}\hbox {C}\) to \(230\,{^{\circ }}\hbox {C}\) with increasing applied voltage from 0 V to 10 V. Furthermore, the thermal diffusivity of the crystalline film was \(1.67\times 10^{-7}\,\hbox {m}^{2}\cdot \hbox {s}^{-1}\) according to the nanosecond thermoreflectance measurements.     

Structural,microstructural and optical properties of $$\hbox {Cu}_{2}\hbox {ZnSnS}_{4}$$ thin films prepared by thermal evaporation: effect of substrate temperature and annealing

Thin films of \(\hbox {Cu}_{2}\hbox {ZnSnS}_{4}\) (CZTS), a promising solar cell absorber, were grown by thermal evaporation of ZnS, Sn and Cu precursors and subsequent annealing in sulphur atmosphere. Two aspects are chosen for investigation: (i) the effect of substrate temperature (\(T_{\mathrm{S}})\) used for the deposition of precursors and (ii) (\(\hbox {N}_{2}{+}\hbox {S}_{2})\) pressure during annealing, to study their impact on the growth of CZTS films. X-ray diffraction analysis of these films revealed the structure to be kesterite with (112) preferred orientation. Crystallite size is found to slightly increase with increase in \(T_{\mathrm{S}}\) as well as pressure during annealing. From optical absorption studies, the direct optical band gap of CZTS films is found to be \({\sim }\)1.45 eV. Room temperature electrical resistivity of the films obtained on annealing the stacks at 10 and 100 mbar pressures is found to be in the ranges 25–55 and 5–25 \(\Omega \) cm, respectively, depending on \(T_{\mathrm{S}}\). Films prepared by annealing the stack deposited at 300\({^{\circ }}\)C under 100 mbar pressure for 90 min are slightly Cu-poor and Zn-rich with compact grain morphology.     

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

Reactionary processes during mechanical treatment of mixtures of ZnO and MnO<Subscript>2</Subscript>. I. Formation of defects and solid solution

Kinetics of defects formation, reaction process and formation of solid solution in powder mixtures of ZnO and MnO₂ induced by prolonged mechanical treatment (MT) have been investigated (X-ray, FTIR, EPR). At MT in zones of deformation-destruction the different defects (\( {\text{V}}_{{\text{Zn}}}^ - :{\text{Zn}}_{\text{i}}^{\text{0}} \) (I), \( {\text{V}}_{{\text{Zn}}}^ - \) (II), and \( {\text{(V}}_{{\text{Zn}}}^ - {\text{)}}_{\text{2}}^ - \) (III) centers at all) are forming. The defects have various physical and chemical properties, and have different activation energies of annealing, E_act The part of these defects is responsible for the processes of hydration and carbonation of samples. In turn, the formation of defects is accompanied by development of various mechanothermical processes, which increase temperature of the sample, T _MT, with the increasing of duration of MT, t _MT. The increasing of t _MT activates the reactionary processes: promotes a consecutive annealing the «low-temperature» defects having small values of E_act (I, II and III) and also leads to formation of Mn²⁺-doped Zn(OH)₂. With the further increase of t _MT, the process of MT is accompanied by an increasing of temperature of samples up to equilibrium, T _eq and accumulation of “high-temperature” defects in the sample. As a result, in the sample the conditions for intensification of volumetric diffusion processes and formation of Mn²⁺-doped ZnO were created.     

Steady-state O<Subscript>2</Subscript> and CO<Subscript>2</Subscript> diffusion in carbonated mortars produced with blended cements

The diffusion coefficient \(D_{{{\text{O}}_{2} }}\), the porosity and the pore structure of mortars produced with a Portland cement and a range of blended cements containing limestone powder, microsilica, portlandite or slag were measured in the non-carbonated and the carbonated state. Additionally, the setup for measuring O₂ diffusion was adapted to measure also the CO₂ diffusion of the carbonated mortars. The diffusion coefficient \(D_{{{\text{O}}_{2} }}\) and the total porosity were increased in the mortars containing microsilica and slag, while they were decreased in the other mortars due to carbonation. Invariably, the pore structure became coarser in all samples. The relationship between diffusion coefficients \(D_{{{\text{O}}_{2} }}\) and \(D_{{{\text{CO}}_{2} }}\) in the carbonated mortars was always linear, with \(D_{{{\text{O}}_{2} }}\) systematically higher by factor of 1.37. As this factor broadly agrees with what was found in the scant literature about CO₂ diffusion, it could be used for estimating \(D_{{{\text{CO}}_{2} }}\) of carbonated mortar and concrete based on measurements of O₂ diffusion.     

Physical,optical and structural studies of copper-doped lead oxychloro borate glasses

Bluish coloured glasses are obtained from the composition PbCl\(_{2}\)–PbO–B\(_{2}\)O\(_{3}\) doped with Cu\(^{2+}\) ions. Basic physical properties and spectroscopic studies (optical absorption, electron paramagnetic resonance, Fourier transform infrared and Raman spectroscopies) were carried out on these samples. The increase in PbCl\(_{2}\) content resulted in the decrease in density and increase in molar volume. At optical frequencies, band gaps and Urbach energies were evaluated and their variation is explained. Spin-Hamiltonian parameters (SHP) obtained from the EPR spectra suggest that the ligand environment around Cu\(^{2+}\) is tetragonally distorted octahedral sites and the orbital \(d_{x^{2}-{y}^{2}} \) is the ground state. The characteristics broad bands in the optical absorption spectra are assigned to the \(^{2}\)B\(_{\mathrm{1g}}\,\rightarrow \, {}^{2}\)B\(_{\mathrm{2g}}\) transition. The bonding coefficient values were evaluated using optical data and SHP. FTIR studies suggested that the glass structure is built up of BO\(_{3}\) and BO\(_{4}\) units. The presence of diborate, pyroborate, pentaborate groups, etc. in the glass network was confirmed from Raman spectra.     

Anisotropy of bituminous mixture in the linear viscoelastic domain

Some anisotropic properties in the linear viscoelastic domain of bituminous mixtures compacted with a French LPC wheel compactor are highlighted in this paper. Bituminous mixture is generally considered as isotropic even if the compaction process on road or in laboratory induces anisotropic properties. Tension–compression complex modulus tests have been performed on parallelepipedic specimens in two directions: (i) direction of compactor wheel movement (direction I, which is horizontal) and (ii) direction of compaction (direction II, which is vertical). These tests consist in measuring sinusoidal axial and lateral strains as well as sinusoidal axial stress, when sinusoidal axial loading is applied on the specimen. Different loading frequencies and temperatures are applied. Two complex moduli, \(E_{\mathrm{I}} ^{*}\) and \(E_{\mathrm{II}}^{*}\), and four complex Poisson’s ratios, \(\nu_{\text{II-I}}^{*}\), \(\nu_{\text{III-I}}^{*}\), \(\nu_{\text{I-II}}^{*}\) and \(\nu_{\text{III-II}}^{*}\), were obtained. The vertical direction appears softer than the other ones for the highest frequencies. There are very few differences between the two directions I and II for parameters concerning viscous effects (phase angles \(\varphi(E_{\mathrm{I}})\) and \(\varphi(E_{\mathrm{II}})\), and shift factors). The four Poisson’s ratios reveal anisotropic properties but rheological tensor can be considered as symmetric when considering very similar values obtained for the two measured parameters (I-II and II-I)In addition, an anisotropic 3 dimensional version of the “2S2P1D” (2 springs, 2 parabolic creep elements and 1 dashpot) model, developed at the University of Lyon—ENTPE laboratory, is presented and used to simulate experimental results. The model simulation provides a good fit to the data. Stability of the material could also be investigated on the whole frequency–temperature range.     

Superconductivity at 25 K under Hydrostatic Pressure for FeTe 0 . 5 Se 0 . 5 Superconductor

We report the impact of hydrostatic pressure on the superconductivity and normal-state resistivity of FeTe_0.5Se_0.5 superconductor. At the ambient pressure, the FeTe_0.5Se_0.5 compound shows the superconducting transition temperature \(T_{\mathrm {c}}^{\text {onset}} \) at above 13 K and \(T_{\mathrm {c}}^{\rho =0} \) at 11.5 K. We measure pressure-dependent resistivity from 250 to 5 K, which shows that the normal-state resistivity increases initially for the applied pressures of up to 0.55 GPa, and then the same is decreased monotonically with increasing pressure of up to 1.97 GPa. On the other hand, the superconducting transition temperatures ( \(T_{\mathrm {c}}^{\text {onset}} \) and \(T_{\mathrm {c}}^{\rho =0} )\) increase monotonically with increasing pressure. Namely the \(T_{\mathrm {c}}^{\text {onset}} \) increases from 13 to 25 K and \(T_{\mathrm {c}}^{\rho =0} \) from 11.5 to 20 K for the pressure range of 0–1.97 GPa. Our results suggest that superconductivity in this class of Fe-based compounds is very sensitive to pressure as the estimated pressure coefficient d T _c(onset)/dP is ～5.8 K/GPa. It may be suggested that the FeTe_0.5Se_0.5 superconductor is a strong electron-correlated system. The enhancement of T _c with applying pressure is mainly attributed to an increase of charge carriers at the Fermi surface.     

A comparative study on dielectric behaviours of Au/(Zn-doped PVA)/<Emphasis Type="Italic">n</Emphasis>-4H-SiC (MPS) structures with different interlayer thicknesses using impedance spectroscopy methods

Three different thicknesses (50, 150 and 500 nm) Zn-doped polyvinyl alcohol (PVA) was deposited on n-4H-SiC wafer as interlayer by electrospinning method and so, Au/(Zn-doped PVA)/n-4H-SiC metal–polymer–semiconductor structures were fabricated. The thickness effect of Zn-doped PVA on the dielectric constant (\(\varepsilon ^{\prime }\)), dielectric loss (\(\varepsilon ^{{\prime }{\prime }}\)), loss-tangent (tan \(\delta \)), real and imaginary parts of electric modulus (\(M^{\prime }\) and \(M^{{\prime }{\prime }})\) and ac electrical conductivity \((\sigma _{\mathrm{ac}})\) of them were analysed and compared using experimental capacitance (C) and conductance (\(G/\omega \)) data in the frequency range of 1–500 kHz at room temperature. According to these results, the values of \(\varepsilon ^{\prime }\) and \(\varepsilon ^{{\prime }{\prime }}\) decrease with increasing frequency almost exponentially, \(\sigma _{\mathrm{ac}}\) increases especially, at high frequencies. The \(M^{\prime }\) and \(M^{{\prime }{\prime }}\) values were obtained from the \(\varepsilon ^{\prime }\) and \(\varepsilon ^{{\prime }{\prime }}\) data and the \(M^{\prime }\) and \(M^{{\prime }{\prime }}\) vs. f plots were drawn for these structures. While the values of \(\varepsilon ^{\prime }\), \(\varepsilon ^{{\prime }{\prime }}\) and tan \(\delta \) increase with increasing interlayer thickness, the values of \(M^{\prime }\) and \(M^{{\prime }{\prime }}\) decrease with increasing interlayer thickness. The double logarithmic \(\sigma _{\mathrm{ac}}\) vs. f plots for each structure have two distinct linear regimes with different slopes, which correspond to low and high frequencies, respectively, and it is prominent that there exist two different conduction mechanisms. Obtained results were found as a strong function of frequency and interlayer thickness.     

Bootstrap in semi-functional partial linear regression under dependence

This paper deals with the semi-functional partial linear regression model \(Y={{\varvec{X}}}^\mathrm{T}{\varvec{\beta }}+m({\varvec{\chi }})+\varepsilon \) under \(\alpha \)-mixing conditions. \({\varvec{\beta }} \in \mathbb {R}^{p}\) and \(m(\cdot )\) denote an unknown vector and an unknown smooth real-valued operator, respectively. The covariates \({{\varvec{X}}}\) and \({\varvec{\chi }}\) are valued in \(\mathbb {R}^{p}\) and some infinite-dimensional space, respectively, and the random error \(\varepsilon \) verifies \(\mathbb {E}(\varepsilon |{{\varvec{X}}},{\varvec{\chi }})=0\). Naïve and wild bootstrap procedures are proposed to approximate the distribution of kernel-based estimators of \({\varvec{\beta }}\) and \(m(\chi )\), and their asymptotic validities are obtained. A simulation study shows the behavior (on finite sample sizes) of the proposed bootstrap methodology when applied to construct confidence intervals, while an application to real data concerning electricity market illustrates its usefulness in practice.     

Canadian Field Soils IV: Modeling Thermal Conductivity at Dryness and Saturation

The thermal conductivity data of 40 Canadian soils at dryness \((\lambda _{\mathrm{dry}})\) and at full saturation \((\lambda _{\mathrm{sat}})\) were used to verify 13 predictive models, i.e., four mechanistic, four semi-empirical and five empirical equations. The performance of each model, for \(\lambda _{\mathrm{dry}}\) and \(\lambda _{\mathrm{sat}}\), was evaluated using a standard deviation (SD) formula. Among the mechanistic models applied to dry soils, the closest \(\lambda _{\mathrm{dry}}\) estimates were obtained by MaxRTCM \((\textit{SD} = \pm ~0.018\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1})\), followed by de Vries and a series-parallel model (\(\hbox {S-}{\vert }{\vert }\)). Among the semi-empirical equations (deVries-ave, Advanced Geometric Mean Model (A-GMM), Chaudhary and Bhandari (C–B) and Chen’s equation), the closest \(\lambda _{\mathrm{dry}}\) estimates were obtained by the C–B model \((\pm ~0.022\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1})\). Among the empirical equations, the top \(\lambda _{\mathrm{dry}}\) estimates were given by CDry-40 \((\pm ~0.021\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1}\) and \(\pm ~0.018\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1}\) for18-coarse and 22-fine soils, respectively). In addition, \(\lambda _{\mathrm{dry}}\) and \(\lambda _{\mathrm{sat}}\) models were applied to the \(\lambda _{\mathrm{sat}}\) database of 21 other soils. From all the models tested, only the maxRTCM and the CDry-40 models provided the closest \(\lambda _{\mathrm{dry}}\) estimates for the 40 Canadian soils as well as the 21 soils. The best \(\lambda _{\mathrm{sat}}\) estimates for the 40-Canadian soils and the 21 soils were given by the A-GMM and the \(\hbox {S-}{\vert }{\vert }\) model.