Crystal structure,thermal behaviour,vibrational spectroscopy and optical properties of new compounds K$$_{}$$Ca(HAsO$$_{4}$$4)$$_{}\cdot $$·H$$_{}$$O with kröhnkite-type chain

The new kröhnkite compound called potassium calcium-bis-hydrogen arsenate dihydrate K\(_{2}\)Ca(HAsO\(_{4})_{2}\cdot \)2H\(_{2}\)O was obtained by hydrothermal method and characterized by X-ray diffraction, infrared spectroscopy, Raman scattering, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis and optical (photoluminescence and absorption) properties. It crystallizes in the triclinic space group P\(\bar{1}\) and unit cell parameters \(a = 5.971(3)\) Å, \(b =6.634(3)\) Å, \(c = 7.856(4)\) Å, \(\alpha =104.532(9)\) \(^{\circ }\), \(\beta = 105.464(9)\) \(^{\circ }\) and \(\gamma = 109.698(9)\) \(^{\circ }\). The structure of K\(_{2}\)Ca(HAsO\(_{4})_{2}\cdot \)2H\(_{2}\)O built up from this infinite, (Ca(HAsO\(_{4})_{2}\)(H\(_{2}\)O)\(_{2})^{2+}\), was oriented along an axis resulting from the association of CaO\(_{6}\) octahedra alternating with each two HAsO\(_{4}\) tetrahedra by sharing corners. Each potassium atom links two adjacent chains by three oxygen atoms of HAsO\(_{4}\) tetrahedra. TGA and DSC have shown the absence of phase transition. The existence of vibrational modes corresponding to the kröhnkite is identified by the IR and Raman spectroscopies in the frequency ranges of 400–4000 and 20–4000 cm\(^{-1}\), respectively. The photoluminescence measurement show one peak at 507 nm, which is attributed to band–band (free electron–hole transitions) and (bound electron–hole transitions) emissions within the AsO\(_{4}\) inorganic part.     

The Damping and Drag Coefficient of Quartz Tuning Fork in Superfluid $$^{3}\hbox {He}$$–$$^{4}\hbox {He}$$4He Solutions in the Laminar Flow

The \(^{3}\)He impurity influence on the oscillations of a quartz resonator and thus its drag coefficient in a laminar flow of a superfluid \(^{3}\)He–\(^{4}\)He mixture has been investigated. The temperature dependences of the resonance curves were measured on quartz tuning forks with a resonance frequency 32 kHz in vacuum in superfluid mixtures with \(^{3}\)He concentrations of \(x_{3}=0.05\) and 0.15 in a wide range of driving forces at temperatures from 0.5–2.5 K. The results obtained were used to plot the temperature dependence of the drag coefficient. With the help of the normalization on the effective area of the oscillating body, the concentration dependence of the drag coefficient of the quartz tuning fork and the vibrating sphere in superfluid solutions has been constructed and analyzed.     

Evolution of magnetic structure of Dy(Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>B<Subscript>2</Subscript>C

DyNi\(_{2}\)B\(_{2}\)C superconducts at \(T_{c} \approx 6\,{\text{K}}\) and orders antiferromagnetically at \(T_{N}\approx 10\,{\text{K}}.\) Its non-superconducting isomorph DyCo\(_{2}\)B\(_{2}\)C is a ferromagnet with \(T_{C}\approx 6\,{\text{K}}.\) With the aim of mapping out the magnetic properties, in particular magnetic structures, of their solid solutions, we synthesized \(^{11}\)B-enriched Dy(Co\(_{x}\)Ni\(_{1-x}\))\(_{2}\)B\(_{2}\)C (\(x=0.2,0.4,0.6,0.8\)). We investigated the evolution of their magnetic, thermal and transport properties by means of the magnetization, resistivity, specific heat and neutron diffraction techniques. Their crystal structures were confirmed to be ThCr\(_{2}\)-Si\(_{2}\)-type tetragonal (I4/mmm) phase. The magnetic structure was found to be antiferromagnetic with k_0.2 = (0, 0, 1) for x = 0.2; helicoidal with k\(_{0.4}\) = (0, 0, 0.49) and k\(_{0.6}\) = (0, 0, 0.46) for, respectively, x = 0.4 and 0.6 and ferromagnetic with k\(_{0.8}\) = (0, 0, 0) for x = 0.8. We discuss the evolution of such magnetic modes assuming a scenario of an idealized one-dimensional chain of transverse magnetic moments.     

Estimating the Kinematic Viscosity of Petroleum Fractions

Kinematic viscosity correlation has been developed for liquid petroleum fractions at 37.78\(\,^{\circ }\hbox {C}\) and \(98.89\,^{\circ }\hbox {C}\) (100 and \(210^{\circ }\hbox {F})\) standard temperatures using a large variety of experimental data. The only required inputs are the specific gravity and the average boiling point temperature. The accuracy of the correlation was compared with several other correlations available in the literature. The proposed correlations proved to be more accurate in predicting the viscosity at 37.78\(\,^{\circ }\hbox {C}\) and \(98.89\,^{\circ }\hbox {C}\) with average absolute deviations of 0.39 and \(0.72\hbox { mm}^{2}/\hbox {s}\), respectively. Another objective was to develop a relation for the variation of viscosity with temperature to predict the viscosity of petroleum fraction at a certain temperature from the knowledge of the viscosity for the same liquid at two other temperatures. The newly developed correlation represents a wide array of temperatures from 20 \(^{\circ }\hbox {C}\) to 150 \(^{\circ }\hbox {C}\) and viscosities from 0.14\(\hbox { mm}^{2}/\hbox {s}\) to 343.64\(\hbox { mm}^{2}/\hbox {s}\). The results have been validated with experimental data consisting of 9558 data points, yielding an overall deviation of \(0.248\hbox { mm}^{2}/\hbox {s}\) and \(\hbox {R}^{2}\) of 0.998. In addition, new formulas were developed to interconvert the viscosity of petroleum fractions from one unit of measure to another based on finding the best fit for a set of experimental data from the literature with \(R^{2}\) as high as 1.0 for many cases. Detailed analysis showed good agreement between the predicted values and the experimental data.     

Thermo-transport properties of Zn-substituted layered Li-nickel oxide, $$\hbox {LiNiO}_{2}$$

The layered Li-TM-\(\hbox {O}_{2}\) materials have been investigated extensively due to their application as cathodes in Li batteries. The electrical properties of these oxides can be tuned or controlled either by non-stoichiometry or substitution. Hence the thermo-transport properties of Zn-substituted \(\hbox {LiNi}_{1-x}\hbox {Zn}_{x}\hbox {O}_{2}\) for \(0 \le x \le 0.16\) have been investigated in the temperature range of 300–900 K for potential application as a high-temperature thermoelectric material. For \(x < 0.08\), the compounds were of single phase belonging to the space group R-3mH while for \(x > 0.08\) an additional minority phase, ZnO forms together with the main layered phase. All the compounds exhibit a semiconducting behaviour with electrical resistivity, varying in the range of  \(\sim 10^{-4}\) to \(10^{-2}\,\,\Omega \hbox {m}\) between 300 and 900 K. The electrical resistivity is found to increase with increasing Zn-substitution predominantly due to a decrease in the charge carrier hole mobility. The activation energy remains constant, \(\sim \)10  meV, with Zn-substitution. The Seebeck coefficient of the compounds is found to decrease with increasing temperature and increase with increasing Zn-substitution. The Seebeck coefficient decreases from \(\sim \)95 to \(35\ \upmu \hbox {V K}^{-1}\) and the corresponding power factor is \(\sim \)12\(\ \upmu \hbox {W m}^{-1}\ {\hbox {K}}^{-2}\) for the \(x = 0.16\) compound.     

Reproducibility of the Helium-3 Constant-Volume Gas Thermometry and New Data Down to 1.9 K at NMIJ/AIST

This study confirms reproducibility of the International Temperature Scale of 1990 (ITS-90) realized by interpolation using the constant-volume gas thermometer (CVGT) of National Metrology Institute of Japan (NMIJ)/AIST with \(^{3}\)He as the working gas from 3 K to 24.5561 K by comparing the newly obtained results and those of earlier reports, indicating that the CVGT has retained its capability after renovation undertaken since strong earthquakes struck Japan. The thermodynamic temperature T is also obtained using the single-isotherm fit to four working gas densities (\(127\,\hbox {mol}\cdot \hbox {m}^{-3}\), \(145\,\hbox {mol}\cdot \hbox {m}^{-3}\), \(171\,\hbox {mol}\cdot \hbox {m}^{-3}\) and \(278\,\hbox {mol}\cdot \hbox {m}^{-3})\) down to 1.9 K, using the triple point temperature of Ne as a reference temperature. In this study, only the second virial coefficient is taken into account for the single-isotherm fit. Differences between T and the ITS-90 temperature, \(T-T_{90}\), reported in earlier works down to 3 K were confirmed in this study. At the temperatures below 3 K down to 2.5 K, \(T-T_{90}\) is much smaller than the standard combined uncertainty of thermodynamic temperature measurement. However, \(T- T_{90}\) seems to increase with decreasing temperature below 2.5 K down to 1.9 K, although still within the standard combined uncertainty of thermodynamic temperature measurement. In this study, T is obtained also from the CVGT with a single gas density of \(278\,\hbox {mol}\cdot \hbox {m}^{-3}\) using the triple-point temperature of Ne as a reference temperature by making correction for the deviation from the ideal gas using theoretical values of the second and third virial coefficients down to 2.6 K, which is the lowest temperature of the theoretical values of the third virial coefficient. T values obtained using this method agree well with those obtained from the single-isotherm fit. We also found that the second virial coefficient obtained by the single-isotherm fit to experimental results agrees well with that obtained by the single-isotherm fit to the theoretically expected behavior of \(^{3}\)He gas with the theoretical second and third virial coefficients at four gas densities used in the present work.     

Measurement of the Nonlinearity of Heat-Flux Sensors Employing a $$\hbox {CO}_2$$ laser

Heat-flux sensors are widely used in industry to test building products and designs for resistance to bushfire, to test the flammability of textiles and in numerous applications such as concentrated solar collectors. In Australia, such detectors are currently calibrated by the National Measurement Institute Australia (NMIA) at low flux levels of 20 W \(\cdot \) m\(^{-2}\). Estimates of the uncertainty arising from nonlinearity at industrial levels (e.g. 50 kW \(\cdot \) m\(^{-2}\) for bushfire testing) rely on literature information. NMIA has developed a facility to characterize the linearity response of these heat-flux sensors up to 110 kW \(\cdot \) m\(^{-2}\) using a low-power \(\hbox {CO}_2\) laser and a chopped quartz tungsten–halogen lamp. The facility was validated by comparison with the conventional flux-addition method, and used to characterize several Schmidt–Boelter-type sensors. A significant nonlinear response was found, ranging from (\(3.2 \pm 0.9\))% at 40 kW \(\cdot \) m\(^{-2}\) to more than 8 % at 100 kW \(\cdot \) m\(^{-2}\). Additional measurements confirm that this is not attributable to convection effects, but due to the temperature dependence of the sensor’s responsivity.     

Measurement of the Inhomogeneity in Type B and Land–Jewell Noble-Metal Thermocouples

Inhomogeneity is the largest contributor to uncertainty in temperature measurements made with thermocouples, and the knowledge of inhomogeneity is essential if low-uncertainty measurements are required. Inhomogeneity is a particular problem for long-term applications at temperatures near or above 1500 \(^{\circ }\hbox {C}\), where pairs of alloyed noble-metal thermocouples must be used and the alloy components and potential contaminants become very mobile and cause large deviations in the Seebeck coefficient. While changes in inhomogeneity are a known and well-studied problem in noble-metal alloys at temperatures below 1100 \(^{\circ }\hbox {C}\), the effects are not well quantified at higher temperatures. This paper reports the first detailed measurements of inhomogeneity in a number of Type B and Land–Jewell thermocouples exposed to either short-term calibration up to 1600 \(^{\circ }\hbox {C}\) or long-term in situ measurements for a period of approximately 3000 h at 1600 \(^{\circ }\hbox {C}\). The inhomogeneity is measured in a high-resolution scanner operating over the range from 600 \(^{\circ }\hbox {C}\) to 900 \(^{\circ }\hbox {C}\). The results show that drifts of between 0.2 % and 0.6 % can be expected for reversible crystallographic and oxidation effects, whereas drift caused by irreversible contamination effects can be expected to be between 0.6 % and 1.1 %. It is also shown that the deviations in emfs caused by irreversible homogeneities in these thermocouples scale approximately linearly with temperature. This scalability allows uncertainties assessed at one temperature, to be extrapolated to other temperatures. Additionally it is shown that a preconditioning anneal at 1100 \(^{\circ }\hbox {C}\) should be applied both before and after calibration to remove undesirable crystallographic and rhodium-oxidation effects.     

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.     

The Influence of Impurities on the Zinc Fixed Point

Impurities are considered to be the most significant source of uncertainty for the realization of the International Temperature Scale of 1990 by means of metal fixed points. The determination and further reduction in this uncertainty require a traceable chemical analysis of dissolved impurities in the fixed-point metal and accurate knowledge of the specific temperature change caused by impurities (slope of the liquidus line). We determined the slope of the liquidus line for three binary systems and present results and conclusions from the chemical analysis of zinc with a nominal purity of 7N. For the Fe–Zn system, we determined a liquidus slope of (\(-0.91\pm 0.14\)) mK / (\(\upmu \hbox {g}{\cdot }\hbox { g}^{-1}\)) from the evaluation of freezing plateaus and (\(-0.76~\pm 0.20\)) mK / (\(\upmu \hbox {g}{\cdot }\hbox { g}^{-1}\)) from the evaluation of melting plateaus; for the Pb–Zn system, the corresponding results are (\(-0.27~\pm 0.05\)) mK / (\(\upmu \hbox {g}{\cdot }\hbox { g}^{-1}\)) and (\(-0.26~\pm 0.05\)) mK / (\(\upmu \hbox {g}{\cdot }\hbox { g}^{-1}\)). Although for the Sb–Zn system, we determined a liquidus slope of about \(-0.8\) mK / (\(\upmu \hbox {g}{\cdot }\hbox { g}^{-1}\)), our investigations showed that a correction of the influence of antimony is highly questionable because antimony can be found in zinc in a fully dissolved state or precipitated as an insoluble compound. Iron is the only impurity where a correction of the fixed-point temperature was possible. For the realization of the zinc fixed point at PTB, this correction is between 2 \(\upmu \)K and 16 \(\upmu \)K depending on the batch of zinc used. The influence of the sum of all impurities was estimated by means of the OME method. The resulting uncertainty contribution is between 12 \({\upmu }\hbox {K}\) and 48 \({\upmu }\hbox {K}\).     

Measurement and Modeling of Mean Activity Coefficients of NaCl in an Aqueous Mixed Electrolyte Solution Containing Glycine

An electrochemical cell with two ion-selective electrodes (Na\(^{+}\) glass) and (Cl\(^{-}\) solid state) was used to measure the mean ionic activity coefficient of NaCl in an aqueous mixture containing NaCl, glycine, and NaNO\(_{3}\) at 308.15 K. The experiments were conducted at fixed molality of NaNO\(_{3}\) (0.1 m) and various molalities of glycine (0–1 m) and NaCl (up to 0.8 m). The experimental data were modeled using a modified version of the Pitzer equation. Finally the activity coefficient ratio of glycine was determined based on the Maxwell equation.     

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.     

Study of Lanthanide Complexes with BTFA in Silica Gels by Photoacoustic Spectroscopy

In this work, lanthanide \(\beta \)-diketonate complexes Ln(btfa)\({}_{3} \cdot 2\hbox {H}_{2}\)O (Ln\(^{3+}\): Eu\(^{3+}\), Sm\(^{3+ }\), and Tb\(^{3+}\); btfa: 4,4,4-trifluoro-l-phenyl-1,3-butanedione) were incorporated into silica gels by a sol–gel method. Photoacoustic (PA) spectra of these complex-doped silica samples were measured and studied. The PA intensity of the \(\beta \)-diketonate ligand is nearly the same for lanthanide complexes in wet gels. After heat treatment at 150 \(^{\circ }\)C, however, the PA intensity of the ligand increases for Eu\(^{3+}\), Sm\(^{3+}\), and Tb\(^{3+}\) complexes in silica gels, respectively. Different PA intensities of the samples are interpreted by comparison with their luminescence spectra. The luminescence result is consistent with the PA spectra. The result indicates that lanthanide \(\beta \)-diketonate complexes cannot be formed in silica gels without a suitable heat treatment. Moreover, the relaxation process model is proposed based on the PA and luminescence results.     

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 and luminescence in sol–gel auto-combustion-synthesized $$\hbox {CaSnO}_{3}{:}\hbox {Eu}^{3+}$$ phosphor

Undoped and Eu-doped \(\hbox {CaSnO}_{3}\) nanopowders were prepared by a facile sol–gel auto-combustion method calcined at \(800{^{\circ }}\hbox {C}\) for 1 h. The samples are found to be well-crystallized pure orthorhombic \(\hbox {CaSnO}_{3}\) structure. Photoluminescence (PL) measurements indicated that the undoped sample exhibits a broad blue emission at about 420–440 nm, which can be recognized from an intrinsic centre or centres in \(\hbox {CaSnO}_{3}\). Eu-doped \(\hbox {CaSnO}_{3}\) showed broad blue emission centred about 434 nm, a weak peak at 465 nm and a sharp intense yellow emission line at 592 nm. The emission situated at 592 nm was assigned to the f–f transition of \(^{5}\hbox {D}_{0}\rightarrow ^{7}\hbox {F}_{1}\) in \(\hbox {Eu}^{3+}\) ions. The afterglow emission and PL decay results in Eu-doped \(\hbox {CaSnO}_{3}\) phosphor, which revealed that there are at least two different traps in this phosphor. From the obtained results, \(\hbox {Eu}^{3+}\)-doped \(\hbox {CaSnO}_{3}\) phosphor could be proposed as a potential white luminescent optical material.     

Positron Annihilation Spectroscopy for Heat-Treated Fe-Ga Alloys and Their Defect Structure

We present the results of lifetime positron annihilation spectroscopy (PALS) for the ferrum–gallium alloys (galfenols) Fe–21at.%Ga and Fe–22.4at.%Ga, whose defect structure changes with annealing from 20 to 1000 \({^\circ }\)C along the phase diagram of Fe\(_{100}\)Ga\(_{100-x}\), at the L12\(\,\rightarrow \,\)A\(_{2}\) transitions and in the sub-lattice of the D0\(_{3}\) phase. In frames of the standard trapping model, we estimate the positron annihilation parameters for the different thermal vacancies. Also we define concentrations of these vacancy defects, which may be helpful to provide an explanation of the physical properties of galfenols, including giant softening and extremal magnetostriction at the given intermetallic composition.     

Thermal Conductivity of Pyroclastic Soil (<Emphasis Type="BoldItalic">Pozzolana</Emphasis>) from the Environs of Rome

The paper reveals the experimental procedure and thermo-physical characteristics of a coarse pyroclastic soil (Pozzolana), from the neighborhoods of Rome, Italy. The tested samples are comprised of 70.7 % sand, 25.9 % silt, and 3.4 % clay. Their mineral composition contained 38 % pyroxene, 33 % analcime, 20 % leucite, 6 % illite/muscovite, 3 % magnetite, and no quartz content was noted. The effective thermal conductivity of minerals was assessed to be about \(2.14\,\hbox {W}{\cdot } \hbox {m}^{-1}{\cdot } \hbox {K}^{-1}\). A transient thermal probe method was applied to measure the thermal conductivity (\(\lambda \)) over a full range of the degree of saturation \((S_{\mathrm{r}})\), at two porosities (n) of 0.44 and 0.50, and at room temperature of about \(25\,^{\circ }\hbox {C}\). The \(\lambda \) data obtained were consistent between tests and showed an increasing trend with increasing \(S_{\mathrm{r}}\) and decreasing n. At full saturation (\(S_{\mathrm{r}}=1\)), a nearly quintuple \(\lambda \) increase was observed with respect to full dryness (\(S_{\mathrm{r}}=0\)). In general, the measured data closely followed the natural trend of \(\lambda \) versus \(S_{\mathrm{r}}\) exhibited by published data at room temperature for other unsaturated soils and sands. The measured \(\lambda \) data had an average root-mean-squared error (RMSE) of \(0.007\,\hbox {W}{\cdot } \hbox {m}^{-1}{\cdot } \hbox {K}^{-1}\) and \(0.008\,\hbox {W}{\cdot } \hbox {m}^{-1}{\cdot } \hbox {K}^{-1}\) for n of 0.50 and 0.44, respectively, as well as an average relative standard deviation of the mean at the 95 % confidence level \((\hbox {RSDM}_{0.95})\) of 2.21 % and 2.72  % for n of 0.50 and 0.44, respectively.     

Influence of Thermal Annealings in Argon on the Structural and Thermochromic Properties of $$\mathrm{MoO}_{3}$$ Thin Films

The effect of thermal annealing in an inert atmosphere (argon) on the structural and thermochromic properties of \(\hbox {MoO}_{3}\) thin films was investigated. \(\hbox {MoO}_{3}\) thin films were deposited by thermal evaporation in vacuum of \(\hbox {MoO}_{3}\) powders. X-ray diffraction patterns of the films showed the presence of the monoclinic Magneli phase \(\hbox {Mo}_{9}\hbox {O}_{26}\) for annealing temperatures above \(250\,{^{\circ }}\hbox {C}\). Absorbance spectra of the films annealed in argon indicated that their thermochromic response increases with the annealing temperature in the analyzed range (23 \({^{\circ }}\hbox {C}\)–300 \({^{\circ }}\hbox {C}\)), a result opposite to the case of thermal annealings in air, for which case the thermochromic response shows a maximum value around 200 \({^{\circ }}\)C–225 \({^{\circ }}\)C and decreases for higher temperatures. These results are explained in terms of a higher density of oxygen vacancies formed upon thermal treatments in inert atmospheres.     

Vacancy-mediated ferromagnetism in Co-implanted ZnO studied using a slow positron beam

Co\(^+\) ions with multiple energies from 50 to 380 keV were implanted into ZnO single crystals up to a total dose of \(1.25\times 10^{17}\,\hbox {cm}^2\). The implanted samples were annealed in open air for 30 min between 200 and 1100 \(^{\circ }\)C. All the samples before and after implantation and annealing were characterized by X-ray diffraction (XRD), Raman scattering and positron annihilation measurements. XRD and Raman scattering measurements indicate that Co implantation induces severe lattice damage, and after annealing the damage recovers gradually. No Co clusters or Co-related second phase was observed in the implanted samples. Doppler broadening of positron annihilation radiation measurements using a slow positron beam reveals a large number of vacancy clusters introduced by Co implantation. After annealing up to 1000 \(^{\circ }\)C, almost all the defects induced by implantation are removed. The implanted samples show clear ferromagnetism measured at 5 K. It shows very slight decrease after annealing at 700 \(^{\circ }\)C and becomes much weaker after annealing at 1000 \(^{\circ }\)C. The origin of ferromagnetism is most probably due to substitution of Co\(^+\) ions at Zn lattice sites. However, it is apparent that the decrease in magnetization after annealing is consistent with the vacancy recovery process, indicating that the ferromagnetism in Co-implanted ZnO is mediated by defects such as Zn vacancy (V\(_{Zn}\)) or vacancy clusters. First principles calculations also support that Zn-related monovacancies and vacancy clusters can enhance the ferromagnetism in Co-doped ZnO.