Cavitation Bubbles Generated by Vibrating Quartz Tuning Fork in Liquid $$^$$He Close to the $$\lambda $$λ-Transition

We report direct optical observation of cavitation bubbles in liquid helium, both in classical viscous He I and in superfluid He II, close to the \(\lambda \)-transition. Heterogenous cavitation due to the fast-flowing liquid over the rough surface of prongs of a quartz tuning fork oscillating at its fundamental resonant frequency of \(4\,\mathrm {kHz}\) occurs in the form of a cluster of small bubbles rapidly changing its size and position. In accord with previous investigators, we find the cavitation threshold lower in He I than in He II. In He I, the detached bubbles last longer than one camera frame (10 ms), while in He II the cavitation bubbles do not tear off from the surface of the fork up to the highest attainable drive.     

Reversibility of the $$\beta \rightleftharpoons \alpha $$ phase transformations in a Pd–Cu solid solution

Thin samples (about 4 μm in thickness) of membrane foil of a Pd–Cu solid solution have been grown on the surface of a SiO₂/Si heterostructure by magnetron sputtering. The key features of \(\beta \rightleftharpoons \alpha \) phase transformations have been identified using X-ray diffraction, Auger electron spectroscopy, energy dispersive X-ray microanalysis, and resistivity measurements during a heating–cooling cycle. The results demonstrate that the phase transformations are reversible only in solid solutions containing an excess of copper in the concentration range corresponding to limiting temperatures near the temperature stability limit of the β-phase. Thermal conditions of membrane element operation have been found that ensure stability of the ordered atomic structure of the foil and, accordingly, its high performance. The \(\beta \rightleftharpoons \alpha \) phase transformation has been shown to be reversible after holding the foil at t = 830°C, in a state with a disordered atomic structure, which ensures restoration of its high hydrogen permeability after diffusion bonding to the case of a membrane element.     

Thermal Properties of Jojoba Oil Between $$20\,{^{\circ }}\hbox {C}$$ and $$45\,{^{\circ }}\hbox {C}$$45∘C

Vegetable oils have been widely studied as biofuel candidates. Among these oils, jojoba (Simmondsia chinensis) oil has attracted interest because it is composed almost entirely of wax esters that are liquid at room temperature. Consequently, it is widely used in the cosmetic and pharmaceutical industries. To date, research on S. chinensis oil has focused on to its use as a fuel and its thermal stability, and information about its thermal properties is scarce. In the present study, the thermal effusivity and conductivity of jojoba oil between \(20\,{^{\circ }}\hbox {C}\) and \(45\,{^{\circ }}\hbox {C}\) were obtained using the inverse photopyroelectric and hot-ball techniques. The feasibility of an inverse photopyroelectric method and a hot-ball technique to monitor the thermal conductivity, and the thermal effusivity of the S. chinensis is demonstrated. The thermal effusivity decreased from 538 \(\hbox {W}\cdot \,\hbox {s}^{1/2}\cdot \,\hbox {m}^{-2}\cdot \,\hbox {K}^{-1}\) to 378 \(\hbox {W}\cdot \,\hbox {s}^{1/2}\cdot \,\hbox {m}^{-2}\cdot \,\hbox {K}^{-1}\) as the temperature increased, whereas the thermal conductivity remained the same over the temperature range investigated in this study. The obtained results provide insight into the thermal properties of S. chinensis oil between \(20\,{^{\circ }}\hbox {C}\) and \(45\,{^{\circ }}\hbox {C}\).     

Hysteresis and Instability in Some IPRT Sensors Within Temperature Ranges Extending from $$-196\,^{\circ }\hbox {C}$$ to $$150\,^{\circ }\hbox {C}$$150∘C

Industrial platinum resistance thermometer (IPRT) sensors or probes suffer from some instability on cycling over significant ranges of temperature and, specifically, from hysteresis in which the resistance tends to follow different paths for increasing temperatures compared with decreasing temperatures. The effect is well known, and cases of quite large hysteresis have been reported in the literature. Therefore, in establishing calibration and measurement capabilities for IPRT calibrations it is important to include an assessment of the performance which can be expected of a ‘typical good’ IPRT and to include this in the overall uncertainty which the laboratory can expect to achieve in such calibrations, even though the effect itself is outside the laboratory’s control. This paper presents results which have been obtained in cycling IPRT probes from four sources within various temperature ranges of current interest at NPL, between \(-196\,^{\circ }\hbox {C}\) and \(150\,^{\circ }\hbox {C}\), to see what levels of hysteresis may be expected. The cycles were carried out quite quickly in order to detect the hysteresis before it was mitigated by relaxation effects, but the time dependence was not itself studied. In most cases, hysteresis was \({<}0.0025\,^{\circ }\hbox {C}\) between \(0\,^{\circ }\hbox {C}\) and \(100\,^{\circ }\hbox {C}\), and \({<}0.0035\,^{\circ }\hbox {C}\) when the range extended down to \(-80\,^{\circ }\hbox {C}\) or up to \(150\,^{\circ }\hbox {C}\). Greater instability occurred when the sensors were cooled to \(-196\,^{\circ }\hbox {C}\).     

Coupled Dynamics for Superfluid $$^4\hbox {He}$$ in a Channel

We study the coupled dynamics of normal and superfluid components of superfluid \(^4\hbox {He}\) in a channel considering the counterflow turbulence with laminar normal component. In particular, we calculated profiles of the normal velocity, the mutual friction, the vortex line density and other flow properties and compared them to the case where the dynamic of the normal component is “frozen.” We have found that the coupling between the normal and superfluid components leads to flattening of the normal velocity profile, increasingly more pronounced with temperature, as the mutual friction, and therefore, coupling becomes stronger. The commonly measured flow properties also change when the coupling between the two components is taken into account.     

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.     

Comparison of the Calibration of Standard Platinum Thermometers by Comparison in the Range from $$-80\,^{\circ }\hbox {C}$$ to $$300\,^{\circ }\hbox {C}$$300∘C

In this paper, an interlaboratory comparison in the field of measurement of temperature is presented. Within the comparison, calibration of a standard platinum resistance thermometer (SPRT) by comparisons in the range from \(-80\,^{\circ }\hbox {C}\) to \(300\,^{\circ }\hbox {C}\) was performed. At the same time, in order to support the calibration and measurement capabilities (CMCs) entries of the participating laboratories, we have registered this as EURAMET Project 1251 (Comparison of the calibration of standard platinum resistance thermometers in the range from \(-80\,^{\circ }\hbox {C}\) to \(300\,^{\circ }\hbox {C}\) by comparison). It was recommended that the participants use their standard procedure for the calibration of the standard platinum resistance thermometers and follow instructions from the protocol of EURAMET Project 1251 during the temperature calibration and, if possible, avoid making extra time-consuming measurements. The interlaboratory comparison was organized by the University of Ljubljana, Faculty of Electrical Engineering, Laboratory of Metrology and Quality (MIRS/UL-FE/LMK) in the scope of the IPA 2011 project. The interlaboratory comparison included a maximum of eleven measurement points. However, certain laboratories did not perform measurements at all points in the range. They have performed only measurements in the range that they cover. Prior to the calibration by comparison in each laboratory, a test measurement at the triple point of water or ice point was done in order to assess the stability of the instruments. Results of the comparison show that all the measurements agree within declared uncertainties and thus supporting declared capabilities of the participating laboratories.     

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.     

Solidification of NaCl–LiF–$$\hbox {CaF}_{2}$$ ternary composites

The purpose of this work is to refine the microstructure of eutectic halides, candidates to polaritonic metamaterials, through the directional solidification of ternary compositions. NaCl–LiF–\(\hbox {CaF}_{2}\) ternary composites have been solidified using Bridgman and micro-pulling-down techniques at pulling rates from 3 to 300 mm/h for the first time. The interparticle spacing is 12% smaller for this composition than for the binary fibrous NaCl–LiF eutectic. Conditions for solidification and growth in order to generate ternary aligned microstructures are discussed. The very small amount of melt remaining in the mixtures until \(580\,^{\circ }\hbox {C}\) is probably the consequence of solid solubility of LiCl in NaCl and the formation of the reciprocal salt pairs, as in NaCl–LiF. However, it does not prevent the solidification of homogenous ternary microstructures.     

Dissociation reaction of the 1/3$$ \left\langle {\bar{1}101} \right\rangle $$ edge dislocation in α-Al2O3

It has been reported that dislocations with 1/3\( \left\langle {\bar{1}101} \right\rangle \) edge component of the Burgers vector are formed in {1\( \bar{1} \)04}/\( \left\langle {11\bar{2}0} \right\rangle \) low-angle grain boundaries of alumina (α-Al₂O₃). These dislocations dissociate into two partial dislocations with a stacking fault on the (0001) plane (Tochigi et al. in J Mater Sci 46:4428–4433, 2011). However, the dissociation reaction of these dislocations has not been determined so far. In this study, the structures of the dissociated dislocations and the (0001) stacking fault were investigated by transmission electron microscopy and theoretical calculations. It was revealed that the dissociated dislocations were generated from the 1/3\( \left\langle {\bar{1}101} \right\rangle \) perfect edge dislocation by the reaction of 1/3\( \left\langle {\bar{1}101} \right\rangle \) → 1/18\( \left\langle {\bar{4}223} \right\rangle \) + 1/18\( \left\langle {\bar{2}4\bar{2}3} \right\rangle \). Furthermore, electron energy loss spectroscopy analysis was performed to examine the atomic/electronic structure of the (0001) stacking fault. In the observed spectra, a chemical shift and intensity decrease were found at the oxygen K-edge. Theoretical spectrum analysis using first-principles calculations revealed that the characteristic features of the spectra are originated from the local atomic configurations of the (0001) stacking fault.     

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.     

Process optimization of dye-sensitized solar cells using $$\hbox {TiO}_{2}$$–graphene nanocomposites

\(\hbox {TiO}_{2}\)–graphene (TGR) nanocomposites with varying concentrations of graphene from 0 to 1 wt% were prepared by direct mix method. X-ray diffraction (XRD) spectra confirmed the incorporation of graphene in photoanode material, which was further supported by field emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX). The UV–visible spectrum of these nanocomposites shifted towards higher wavelength region as compared to pure \(\hbox {TiO}_{2}\) that indicated a reduced band gap and hence, enhanced absorption bandwidth. Significant reduction in electron–hole recombination was confirmed from photoluminescence spectroscopy. These TGR nanocomposite films after tethering with black dye were employed as photoanodes in dye-sensitized solar cells (DSSCs). The efficiency of solar cells at varying concentrations of graphene (in photoandes) was also investigated. TGR 0.25 wt% nanocomposite showed the highest photocurrent density (\(J_{\mathrm{SC}}\)) of \(18.4\,\hbox {mA}\,\hbox {cm}^{-2}\) and efficiency (\(\eta \)) of 4.69%.     

Enhanced infrared transmission characteristics of microwave-sintered $$\hbox {Y}_{2}\hbox {O}_{3}$$–$$\hbox {MgO}$$MgO nanocomposite

Infrared (IR) transparent ceramics are found to have applications in demanding defence and space missions. In this work, \(\hbox {Y}_{2}\hbox {O}_{3}\)–\(\hbox {MgO}\) nanocomposites were synthesised by a modified single-step combustion technique. The characterisation of the as-prepared powder by X-ray diffraction and transmission electron microscopy revealed the presence of cubic phases of ultra-fine nanostructured \(\hbox {Y}_{2}\hbox {O}_{3 }\) and MgO, with an average crystallite size of \({\sim }19 \hbox { nm}\). For the first time the resistive and microwave heatings were effectively coupled for sintering the sample, and it was found that the sintering temperature and soaking time were reduced considerably. The pellets were sintered to 99.2% of the theoretical density at \(1430{^{\circ }}\hbox {C}\) for a soaking duration of 20 min. The well-sintered pellets with an average grain size of \({\sim }200 \hbox { nm}\) showed better transmittance properties relative to pure yttria. The promising percentage transmission of 80% in the UV–visible region and 82% in the mid-IR region shown by \(\hbox {Y}_{2}\hbox {O}_{3}\)–\(\hbox {MgO}\) nanocomposites can be tailored and made cost-effective to fabricate high-quality IR windows for strategic defence and space missions.     

Atomic and electronic structure of [0001]/($$\bar{1}\bar{2}30$$) Σ7 symmetric tilt grain boundary in ZnO bicrystal with linear current-voltage characteristic

The atomic and electronic structures of [0001]/( ) Σ 7 symmetric tilt grain boundary in an undoped ZnO bicrystal were investigated by high-resolution transmission electron microscopy (HRTEM) and first-principles calculations. HRTEM imaging and atomistic calculations revealed that the grain boundary was composed of at least two types of structural units. It was also found that one of the structural units has two threefold-coordinated atoms per a unit and the other has two fivefold-coordinated atoms. First-principles calculations indicated that these atoms with various coordination numbers do not form deep unoccupied electronic states in the band gap of ZnO, which is in consistency with a linear current-voltage characteristic observed for the bicrystal with the Σ 7 boundary.     

Polymer-assisted co-precipitation route for the synthesis of Al$$_{}$$O$$_{3}$$3–13% TiO$$_{}$$ nanocomposite

The present investigation reveals the effect of processing parameters on the properties of alumina–titania (Al\(_{2}\)O\(_{3}\)–TiO\(_{2}\)) nanocomposites. A polymer-assisted (Pluronic P123 triblock co-polymer) co-precipitation route has been employed to synthesize \(\hbox {Al}_{2}\hbox {O}_{3}\)–\(\hbox {TiO}_{2}\) nanoparticles. As a surfactant, pluronic P123 polymer exhibits hydrophobic as well as the hydrophilic nature simultaneously which detains the agglomeration and hence the nano size particle have been obtained. Effect of surfactant concentration on morphology and particle size of product has also been investigated. Thermal behaviour of the prepared powder samples have been studied using differential scanning calorimeter/thermal gravimetric analysis and dilatometer. Formation of aluminium-titanate \((\hbox {Al}_{2}\) \(\hbox {TiO}_{5})\) phase has been confirmed using X-ray diffraction analysis. It has been observed by field emission scanning electron microscopy analysis that the particle size reduced effectively (below 100 nm) when polymer-assisted co-precipitation route is used instead of the simple co-precipitation technique. A highly dense microstructure of sintered samples has been obtained, driven by reduced particle size.     

Vortex Shedding from an Object Moving in Superfluid $$^4\hbox {He}$$ at mK Temperatures and in a Bose–Einstein Condensate

Vortex shedding from a microsphere oscillating in superfluid \(^4\hbox {He}\) at mK temperatures is compared with that from a laser beam moving in a Bose–Einstein condensate as observed by other authors. In particular, in either case a linear dependence of the shedding frequency \(f_v\) on \(\varDelta v = v - v_c\) is observed, where v is the velocity amplitude of the sphere or the constant velocity of the laser beam above a critical velocity \(v_c\) for the onset of turbulent flow: \(f_v = a \,\varDelta v\), where the coefficient a is proportional to the oscillation frequency \( \omega \) above some characteristic frequency \(\omega _k\) and assumes a finite value for steady motion \(\omega \rightarrow 0\).     

Photoacoustic Spectroscopic Study of Optical Properties of $$\hbox {Cu}_{2}\hbox {GeTe}_{3}$$ in Temperature Range from 80 K to 300 K

We used photoacoustic spectroscopy to investigate the optical properties of \(\hbox {Cu}_{2}\hbox {GeTe}_{3}\). The temperature dependence of the bandgap energy was evaluated from optical absorption spectra obtained in the photon energy range of 0.76 eV to 0.81 eV between 80 K and 300 K. We used the empirical and semi-empirical models of Varshni, Viña, and Pässler to describe the observed bandgap shrinkage in this compound. The Debye temperature and effective phonon temperature of the compound were estimated to be approximately 227.4 K and 151.6 K, respectively. Thus, the temperature dependence of the bandgap is mediated by acoustic phonons.     

Thermodynamic Investigation of the Eutectic Mixture of the $$\hbox {LiNO}_{3}$$–$$\hbox {NaNO}_{3}$$NaNO3–$$\hbox {KNO}_{3}$$KNO3–$$\hbox {Ca}(\hbox {NO}_{3})_{2}$$Ca(NO3)2 System

Molten nitrate salt is usually employed as heat transfer or energy storage medium in concentrating solar power systems to improve the overall efficiency of thermoelectric conversion. In the present work, the liquidus curves of the \(\hbox {LiNO}_{3}\)–\(\hbox {NaNO}_{3}\)–\(\hbox {KNO}_{3}\)–\(\hbox {Ca}(\hbox {NO}_{3})_{2}\) system is determined by conformal ionic solution theory according to the solid–liquid equilibrium state of the binary mixture. The calculated eutectic temperature of the mixture is \(93.17\,{^{\circ }}\hbox {C}\), which is close to the experimental value of \(93.22\,{^{\circ }}\hbox {C}\) obtained from differential scanning calorimetry (DSC). Visualization observation experiments reveal that the quaternary eutectic mixture begins to partially melt when the temperature reaches \(50\,{^{\circ }}\hbox {C}\), and the degree of melting increases with temperature. The mixture is completely melted at \(\hbox {130}\,{^{\circ }}\hbox {C}\). The observed changes in the dissolved state at different temperatures correlate well with the DSC heat flow curve fluctuations.     

Optimization of the liquid–liquid interfacial precipitation method for the synthesis of $$\hbox {C}_{60}$$ nanotubes

Tubular fullerene nanowhiskers called ‘fullerene nanotubes’ are composed of \(\hbox {C}_{60}\) fullerene molecules (\(\hbox {C}_{60}\) NTs) are synthesized at room temperature using the liquid–liquid interfacial precipitation method in the pyridine and isopropyl alcohol (IPA) system. The growth control of fullerene nanotubes is important for their chemical and physical properties as well as for their future applications. In the present study, we investigated the effect of light, water, solvent ratio and temperature on the synthesis of \(\hbox {C}_{60}\) nanotubes. A marked development in the yield of \(\hbox {C}_{60}\) NTs was achieved using dehydrated solvents, a solution with a volume ratio of 1:9 for pyridine: IPA, a growth temperature equal to \(5{^{\circ }}\hbox {C}\) and by illuminating the \(\hbox {C}_{60}\)-pyridine solution with ultraviolet light (wavelength 302 nm) for 102 h. The synthesized fullerene nanotubes were characterized by different analytical techniques including Raman and Fourier transform infrared spectroscopy, optical microscopy, focussed ion beam scanning electron microscopy and transmission electron microscopy.     

Synthesis of $$\hbox {Ag}_{2}\hbox {Se}$$–graphene–$$\hbox {TiO}_{2} $$TiO2 nanocomposite and analysis of photocatalytic activity of $$\hbox {CO}_{2}$$CO2 reduction to $$\hbox {CH}_{3}\hbox {OH}$$CH3OH

The present work deals with the development of a new ternary composite, \(\hbox {Ag}_{2}\hbox {Se}\)–\(\hbox {G}\)–\(\hbox {TiO}_{2}\), using ultrasonic techniques as well as X-ray diffraction (XRD), scanning electron microscopy (SEM), high transmission electron microscopy (HTEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and UV–Vis diffuse reflectance spectra (DRS) analyses. The photocatalytic potential of nanocomposites is examined for \(\hbox {CO}_{2}\) reduction to methanol under ultraviolet (UV) and visible light irradiation. \(\hbox {Ag}_{2}\hbox {Se}\)–\(\hbox {TiO}_{2}\) with an optimum loading graphene of 10 wt% exhibited the maximum photoactivity, obtaining a total \(\hbox {CH}_{3}\hbox {OH}\) yield of 3.52 \(\upmu \hbox {mol}\,\hbox {g}^{-1}\,\hbox {h}^{-1}\) after 48 h. This outstanding photoreduction activity is due to the positive synergistic relation between \(\hbox {Ag}_{2}\hbox {Se}\) and graphene components in our heterogeneous system.