Low Temperature Part Research Articles

Crystal and thermodynamic properties of [formula omitted], (X = Al, Ga)

The crystal and thermodynamic properties of Tb2Ni2X (X = Al, Ga) are reported through measurements of X-ray diffraction (XRD), magnetic susceptibility, χ(T), magnetization, M(μ0H) and heat capacity, Cp(T). XRD pattern analysis confirms the orthorhombic W2CoB2-type structure with the space group of Immm. χ(T) at high temperature for both compounds follows the Curie – Weiss relationship giving an effective magnetic moment close to that expected for the trivalent Tb ion. The low-temperature χ(Cp) data indicate that both compounds order antiferromagnetically at TN = 41 K (40.4 K) and 41.5 K (41.4 K) for Al and Ga compounds, respectively. Cp(T) data of the nonmagnetic counterparts Y2Ni2X (X = Al, Ga) are well described by the Debye model giving a Debye temperature, θD = 236.9(4) K and 225.3(2) K for Al and Ga compounds, respectively. The low-temperature part of the 4f-magnetic contribution to the total heat capacity, C4f(T) can be described by the antiferromagnetic spin-wave dispersion, giving an energy gap Δsw = 47(3) K and 26(2) K for Al and Ga compounds, respectively. The 4f – magnetic entropy S4f(T) for both compounds reaches the value of 2Rln(2) close to their respective TN values.

Experimental study on vibration reduction of a cryogen-free dilution refrigerator system pre-cooled by a GM cryocooler

In order to carry out vibration reduction work on a cryogen-free dilution refrigerator system pre-cooled by a GM cryocooler, this paper first introduces the method of vibration measurement, particularly presenting the results and verification of displacement measurement obtained through acceleration integration. Subsequently, based on the construction of our dilution refrigerator, the paper reports experimental evidence of the direct impact of vibration on temperature and provides an effective vibration reduction scheme for the system. The study finds that vibrations transmitted through the path of “low-temperature part of GM- copper braid − support structure − various cold plates” have the most significant impact, hence making good internal soft connections is key. The influence of vibrations from the room-temperature part of GM can be mitigated to some extent by suspending the cold head, either by a separate frame or using the dilution refrigerator’s own frame. The use of a structure composed of air springs and honeycomb rubber in the suspension system has proven to be effective. Our final experimental results have demonstrated that with adequate vibration damping, the impact of vibrations from the GM on temperature can be essentially eliminated, allowing the dilution refrigerator to achieve a temperature level close to that when pre-cooled by a PT. The research in this paper has certain reference value for the construction and vibration mitigation of ultra-low temperature refrigeration systems.

Intermediate valence behavior of the ternary cerium-nickel-phosphide Ce2Ni12P5

The crystal structure of the ternary phosphide Ce2Ni12P5 (La2Ni12P5-type structure) has been determined from X-ray powder diffraction data: full profile refinement, monoclinic symmetry, space group P21/m, a = 10.7809(2) Å, b = 3.6869(1) Å, c = 13.1490(3) Å, β = 107.776(4)º, RI = 0.068, RP = 0.044, RwP = 0.060. Ce2Ni12P5 is a ferromagnet with a Curie temperature of 5.8(5) K. A significant deviation from the linearity of the temperature dependence of the electrical resistance for Ce2Ni12P5 has been found. The low-temperature part of the electrical resistance indicates the presence of magnetic interactions in Ce2Ni12P5. The influence of a magnetic field on the electrical resistance of Ce2Ni12P5 has been studied. The X-ray absorption spectrum at the Ce LIII edge and X-ray emission spectra of Ni and P at the K and LIII edges have been studied experimentally and theoretically using DFT+U calculations. The calculations show good agreement with the experimental measurements. The effective valence of Ce in Ce2Ni12P5 determined based on the Ce LIII absorption spectrum is ϑeff ∼ 3.05.

Electrical conductivity of copper in the low temperature region of warm dense matter

In this study, electrical conductivity of copper in the low temperature part of a warm dense matter regime is investigated utilizing underwater electrical wire explosion. Specifically, for the vapor/plasma region with a density of ∼0.01 normal density, temperature up to 10 kK, and the liquid–vapor two-phase region below the binodal curve, the electrical conductivity of copper is measured as a function of density and temperature by means of shadowgraph imaging, spectroscopy, and electrical measurements. In this region, anomalous temperature dependence and characteristics originated from a phase transition are found. Based on the careful analysis of experiments and model calculations, it is revealed that bound electrons, in addition to free electrons, contribute significantly to the electrical conductivity in the vapor/plasma region, and that the associated phase transition kinetics play a substantial role in adequately describing the behavior in the liquid–vapor two-phase region. An improved electrical conductivity model emerging from our combined experimental and theoretical study that accounts for the characteristics in the low temperature regime of the warm dense matter is presented.

Effect of cooling rate on the precipitation characteristics and growth mechanism of Bi3Ni in liquid lead‑bismuth eutectic

Austenitic stainless steel is a promising candidate structural material for direct contact components with lead‑bismuth eutectic (LBE) in lead-cooled fast reactor (LFR). However, the preferential dissolution of Ni from austenitic steels at low oxygen concentrations will lead to the precipitation of Ni-containing phases in the low-temperature parts of reactors, which has a risk of pipe clogging. In this paper, three samples, comprising one extracted from a corrosion tank after prolonged operation and two prepared, respectively, by quenching in liquid nitrogen and cooling in the furnace, were obtained to investigate the effect of cooling rate on the precipitation characteristics and growth mechanism of Bi3Ni that forms by the reaction of dissolved Ni and Bi in LBE. The results showed that rod-like Bi3Ni was found in all three Ni-containing LBE samples. As the cooling rate increased, the width of Bi3Ni decreased. The Bi3Ni in all three samples displayed a pseudo-hexagonal prismatic shape and had a typical faceted growth character; the cooling rate had no effect on the morphology of them. The crystallographic analysis showed that the growth axis of Bi3Ni was in the 〈010〉 direction, and the prism planes were composed of {001} and {101}. In addition, the precipitation of Bi3Ni inevitably increased the content of Pb7Bi3, which would in turn enhance the volumetric expansion of solid LBE samples. For the growth mechanism, Bi3Ni phases were controlled by the screw dislocation mechanism, with the step growth rate of the dislocation core being greater than that of the outer edges. Given the low cooling rate and low Ni content in the LBE coolant of reactors, the precipitation of Bi3Ni with a rod-like morphology seems to be inevitable.

Thermoluminescence characteristics of gamma-irradiated nano-alumina

The focus of this study lies in exploring the properties of thermoluminescence (TL) in nano-alumina, including the correlation between TL intensity and absorbed dose, identification of individual luminescence peaks, and investigation of trap parameters for potential dosimetry applications. The samples were irradiated by 60Co with doses ranging from 530 to 2646 Gy. Micro-sized α-Al2O3 had a prominent dosimetry peak at maximum temperature Tm = 435 K. Nano-α-Al2O3 samples with 40 and 50 nm particle sizes exhibited a TL luminescence glow curve, with the main dosimetry peak in the low-temperature region and a complex structure at higher temperatures (above 500 K). The observed maximum of the main dosimetry peak depended on the nanoparticle size and was 460 K for the sample with particle size of 40 nm and 467 K for 50 nm. The main dosimetry peak was described by the superposition of the two peaks.A computerized glow curve deconvolution method was applied to determine the parameters of the traps responsible for TL using the Microsoft Windows-operated GlowFit program, assuming first-order kinetics. The found values of the activation energies were 0.97 ± 0.01 eV for the trapping center responsible for the peak with Tm = 458 ± 3 K and, accordingly, 1.05 eV for the peak with Tm = 473 ± 3 K. The estimated values of the frequency factor were s ≈ 1.01 × 1010 and 1.3 × 1010 s−1 for the peak with Tm = 458 ± 3 K, and 2.06 × 1011 s−1 for the peak with Tm = 473 ± 3K, respectively. The lifetime for the traps in nano-α-Al2O3 was estimated as 43–56 days for the first trap and approximately 65 days for the second trap. It is assumed that these traps are responsible for TL emission at the low-temperature part of the glow curve.

Stochastic planning of integrated energy system based on correlation scenario generation method via Copula function considering multiple uncertainties in renewable energy sources and demands

AbstractThe main goal of integrated energy service providers (IESP) in the future is to pursue profitability and reduce carbon emissions while ensuring sufficient energy supply. However, the multiple uncertainties associated with renewable energy resources and the multi‐energy consumers pose significant challenges in the optimal planning of the integrated energy system (IES) based on energy hubs (EH). This includes the global optimization of device types, EH capacity, and the optional interconnections between adjacent EHs. This study aims to develop a comprehensive mathematical model of EH that considers the temperature limitations on device operation. The thermal bus and associated devices are divided into high and low temperature parts, and a multi‐scenario stochastic programming model is proposed for IES planning. Scenarios are generated using non‐parametric kernel density estimation and the Copula function, a scenario reduction technique is implemented to alleviate computational burden. Additionally, case studies illustrate effectiveness of the proposed approach, the operation and forms of EHs, effect of the interconnections and the trade‐off between carbon emissions and economic costs are further studied by extensive simulations. This study can be a good guide for IESPs to invest in the construction of the EH‐based IES.

The Thermoluminescence Parameters of Irradiated K-Feldspar

Isothermal decay of the TL glow curve has been studied at ambient temperature. Heating of feldspar at 600ºC leads to increased sensitivity of the samples upon irradiation for the whole range of glow curve. In general, we observe a sensitivity increase of about five times. Fading of the glow curve is observed at the low-temperature part of the glow curve while it has been kept in the dark at the ambient, constant temperature. After a certain period, approximately in 40 to 50 days, the low-temperature region of the glow curve fades down while the high-temperature part remains unchanged. Peaks at the low-temperature region of the TL glow curve were isolated by the curve subtraction method. Activation energy and frequency factor parameters of the isolated peaks were calculated, taking first and second-order kinetics into account. The values of the calculated activation energy vary between 0.7 to 1.1 eV, and frequency factor values of the isolated peaks change within the order of 109 to 1013s-1. The µ values clearly indicate that all isolated peaks are more likely to be second-order kinetics.

Organomorphic Silicon Carbide Reinforcing Preform Formation Mechanism

Development of the organomorphic ceramic-matrix composites (CMCs), where the reinforcing preform is built using polymer fibers subject essentially to hot pressing, was motivated by a desire to obtain much higher structural uniformity as well as to reduce the number of the process steps involved in the production of CMCs. This paper addresses the peculiarities of the organomorphic silicon carbide preform formation process. Using X-ray phase analysis, tomography, mass and IR spectroscopy, and thermomechanical and X-ray microanalysis, both the properties of the initial fibers of polycarbosilane (PCS)—the silicon carbide fiber precursor—and their transformation in the preform while heated to 1250 °C under constant pressing at 10–100 kPa were studied. Analysis of the data obtained showed the organomorphic SiC preform relative density at a level of 0.3–0.4 to be ensured by self-bonding of the silicon carbide preform, resulting from the fact that during the low-temperature part of pyrolysis, easily polymerizing substances are released leaving a high coke residue, thus cementing the preform. Another possible factor of SiC framework self-bonding is the destruction of the polymer fibers during pyrolysis of various PCS preforms differing in their methylsilane composition (for example, dimethylsilane), where deposition of silicon carbide on the contacting fibers starts as early as at 450–500 °C.

Effect of active cooling on the thermal effect of electromagnetic rail under single launch mode

In order to investigate the influence of active cooling on the rail thermal effect of electromagnetic gun under single launch mode, characteristics of the peak temperature, cross-section current density and temperature distribution, axial temperature distribution of rail with and without active cooling are simulated. In addition, the time-varying characteristics of the rail axial temperature distribution, the temperature time-varying characteristic in different temperature parts on the rail and the influence of the cooling water flow velocity on the temperature in different temperature parts are experimentally studied. The results show that during the launch, there is almost no difference between the rail peak temperature and its location with and without active cooling, and the peak temperature is basically located at the initial position of the armature. Without active cooling, the rail axial temperature distribution shows a trend of higher at the gun tail and lower at the gun muzzle. The current density and temperature distribution of rail cross-section show a trend of higher on the rail inner side and lower on the rail outer side, and the diffusion of heat lags behind the diffusion of current. Under the action of active cooling, the rail peak temperature will move to the muzzle along the armature moving direction, and there is a “thermal inversion” phenomenon. The rail cross-section temperature drops faster, and the lowest temperature region appears near the middle cooling channel. Active cooling has different effects on rail temperature in different temperature parts. In the high-temperature part, the rail temperature decreases monotonically with the increase of cooling water flow velocity, increasing the water velocity can accelerate the decline of rail temperature. In the middle-temperature parts, the variation trend of rail temperature is different with different water flow velocities. At low water velocity, the rail temperature increases gradually. When the water flow velocity is greater than 0.75 m/s, the phenomenon of “thermal inversion” will occur. i.e., the rail temperature increases first and then decreases. In the low-temperature part, “thermal inversion” will occur at different flow velocities, that is, the rail temperature increases first and then decreases. When the water flow velocity is greater than 1.0 m/s, the improvement of rail cooling effect will no longer be obvious. It is suggested that the appropriate water flow velocity is 0.75–1.0 m/s under the present experimental conditions.

Basic Study on Power Transmission Characteristics for High-Temperature Superconducting Cable Termination Applying a Wireless Power Transmission System

We devised an HTS cable termination applying a wireless power transmission (WPT) system. The WPT system for the HTS cable termination can mechanically separate the HTS cable (low temperature part) from the copper cable (normal temperature part). In order to clarify the feasibility and design guidelines of the WPT system for the HTS cable termination, it is necessary to investigate the power transmission characteristics of the WPT system using the HTS and copper coils. In this study, we analyzed the power transmission characteristics of the simple WPT model system for the HTS cable termination by an equivalent circuit model and a finite element method analysis, and investigated the basic coil structure for the HTS cable termination applying the WPT system. As a result, the high-efficiency WPT system for the HTS cable termination can be realized by increasing the transport current of the HTS coil more than that of the copper coil. Also, we found that the HTS-Cu system using the primary-side HTS coil and the secondary-side copper coil is suitable for the HTS cable termination applying the WPT system.

Construction Status of the Superconducting Magnet System for the COMET Experiment

The COMET experiment, which is being prepared at the Japan Proton Accelerator Research Complex (J-PARC), aims to explore the rare decay phenomenon of muons. This phenomenon is not allowed in the Standard Model of elementary particles but is expected to occur due to new physics beyond the Standard Model. In the COMET experiment, superconducting magnets are used throughout the muon beamline. The Pion Capture Solenoid concentrates the pions generated by the injection of proton beams into the target. Since this magnet surrounds the target, it is designed to operate in a high radiation environment. The Muon Transport Solenoid guides the muons generated by the decay of pions. This magnet maximizes the muon yield and reduces the other background particles. The Detector Solenoid acts as a spectrometer of the electrons generated by the decay of muons. These low-temperature superconducting magnets are now being developed and constructed. The current lead box is also constructed to supply high currents to the magnets. It provides a thermal gradient from the room-temperature part of the power supply to the low-temperature part of the coil. It is designed to provide a large thermal gradient over a short distance using high-temperature superconductors. Using the current lead box, all magnets, including the high-temperature superconducting leads, are cooled by conduction cooling. In this paper, the construction status of the COMET superconducting magnet system is reported.

Ising ferromagnets and antiferromagnets in an imaginary magnetic field.

We study classical Ising spin-1/2 models on a two-dimensional (2D) square lattice with ferromagnetic or antiferromagnetic nearest-neighbor interactions, under the effect of a pure imaginary magnetic field. The complex Boltzmann weights of spin configurations cannot be interpreted as a probability distribution, which prevents application of standard statistical algorithms. In this work, the mapping of the Ising spin models under consideration onto symmetric vertex models leads to real (positive or negative) Boltzmann weights. This enables us to apply accurate numerical methods based on the renormalization of the density matrix, namely, the corner transfer matrix renormalization group and the higher-order tensor renormalization group. For the 2D antiferromagnet, varying the imaginary magnetic field, we calculate with high accuracy the curve of critical points related to the symmetry breaking of magnetizations on the interwoven sublattices. The critical exponent β and the anomaly number c are shown to be constant along the critical line, equal to their values β=1/8 and c=1/2 for the 2D Ising model in a zero magnetic field. The 2D ferromagnets behave in analogy with their 1D counterparts defined on a chain of sites, namely, there exists a transient temperature which splits the temperature range into its high-temperature and low-temperature parts. The free energy and the magnetization are well defined in the high-temperature region. In the low-temperature region, the free energy exhibits singularities at the Yang-Lee zeros of the partition function and the magnetization is also ill-defined: It varies chaotically with the size of the system. The transient temperature is determined as a function of the imaginary magnetic field by using the fact that from the high-temperature side both the first derivative of the free energy with respect to the temperature and the magnetization diverge at this temperature.

Mechanism to form ring-like distributed oxidation-induced stacking fault bands through relaxing thermal stress during stopping the growth in CZ silicon crystals

This paper aims to study the mechanism to form ring-like distributed oxidation-induced stacking fault (R-OSF) bands in CZ silicon. In this experiment, pulling crystals was stopped during the growth, and the crystals were held for predetermined periods contacting the melt while the seed rotation and converse crucible rotation were maintained. Then, the crystals were detached from the melt and cooled rapidly to freeze the defect distribution. In CZ crystals during the growth, high-temperature mass (crystalized silicon) is transferred upward from the growth interface with the crystal pulling. The top of the crystals is directly cooled by the cooling water chamber, while the peripheral part is heated by the radiation from the heater through the gap under the heat shield and the radiation from the melt surface. Thus, the temperature of the upper center part becomes lower than that of the peripheral part, and isotherms in the crystal form U-shape. When the growth is stopped, the crystals also stop raising the “high-temperature mass” from the growth interface. Thus, cooling rapidly proceeds from the center upper part to the growth interface, and the U-shape isotherms fall downward. When the temperature of a region along a U-shaped isotherm decreases to around 1000 ℃, and a temperature gradient exceeding a certain threshold also forms vertically to the U-shaped isotherm, a thermal stress (expansion stress) is applied from the high-temperature side part to the low-temperature center part. At this time, oxygen precipitates, the nuclei of the R-OSFs, are presumably generated there to relax the thermal stress. Although some researchers have presumed that the R-OSF band is a vacancies (Vs)/interstitials (Is) boundary formed at a temperature near the melting point, the results of this study contradict their presumption.

Low-temperature metastable-to-equilibrium phase transitions in Fe–Ga alloys

Significant differences between the properties of Fe–Ga alloys (Galfenols) in their metastable and equilibrium states, as well as discrepancies between existing Fe–Ga phase diagrams and for the transition rates for the metastable to equilibrium state have been detected and discussed. In view of both the fundamental understanding and the technological importance of these alloys, the exact knowledge of the equilibrium phase diagram, metastable phases, and the transition rates between different phase states towards equilibrium are necessary and require further clarification. We have studied the influence of alloy composition, annealing temperature and annealing time (up to 1800 h) on the metastable-to-equilibrium phase transitions in binary Fe–Ga using a coherent set of complementing methods, including diffraction methods (X-ray and neutron diffraction), scanning electron microscopy, and electron backscatter diffraction. We propose several important changes to the low-temperature part of the binary Fe–Ga diagram close to the Fe-rich corner and a new method based on interdiffusion couples for varying the structure and phase states of Fe–Ga alloys.

High temperature superconductivity in the candidate phases of solid hydrogen

As the simplest element in nature, unraveling the phase diagram of hydrogen is a primary task for condensed matter physics. As conjectured many decades ago, in the low-temperature and high-pressure part of the phase diagram, solid hydrogen is expected to become metallic with a high superconducting transition temperature. The metallization may occur via band gap closure in the molecular solid or via a transition to the atomic solid. Recently, a few experimental studies pushed the achievable pressures into the 400–500 GPa range. There are strong indications that at some pressure in this range metallization via either of these mechanisms occurs, although there are disagreements between experimental reports. Furthermore, there are multiple good candidate crystal phases that have emerged from recent computational and experimental studies which may be realized in upcoming experiments. Therefore, it is crucial to determine the superconducting properties of these candidate phases. In a recent study, we reported the superconducting properties of the C2/c-24 phase, which we believe to be a strong candidate for metallization via band gap closure (Dogan et al 2022 Phys. Rev. B 105 L020509). Here, we report the superconducting properties of the Cmca-12, Cmca-4 and I41/amd-2 phases including the anharmonic effects using a Wannier function-based dense k-point and q-point sampling. We find that the Cmca-12 phase has a superconducting transition temperature that rises from 86 K at 400 GPa to 212 K at 500 GPa, whereas the Cmca-4 and I41/amd-2 phases show a less pressure-dependent behavior with their T c in the 74–94 K and 307–343 K ranges, respectively. These properties can be used to distinguish between crystal phases in future experiments. Understanding superconductivity in pure hydrogen is also important in the study of high-T c hydrides.

Reduction on the inefficiency of heat recovery storage in a compressed carbon dioxide energy storage system

A growing boom can be noticed at the area of energy storage in recent years as this technology can address the supply-demand problem of power generation. As one of the most cutting edge energy storage technologies, the compressed carbon dioxide energy storage captures an increasing number of eyes all over the world. However, large inefficiencies occur within heat exchangers in supercritical pressure with resulting in low system efficiency. Therefore, a new thermal energy storage configuration is designed by separating the supercritical heat exchangers into two parts in which different mass of thermal storage medium is provided to adapt to the specific heat of supercritical CO2, such as 0.45 kg/s for the high-temperature part and 0.76 kg/s for the low-temperature part. Detailed thermodynamic analysis is conducted to identify the superiority of the new configuration compared to the traditional one. The analysis results indicate that the heat transfer between supercritical CO2 and water enjoys much better temperature match in the improved system. The round trip efficiency of improved system can arrive at 57.85% with the optimized final cooler temperature at 32 °C, 5.26% higher than the baseline system with optimized final cooled temperature located at 48 °C. In the improved system, the optimized operation ranges of charge pressure and discharge pressure are at 15–17 MPa and 14–16 MPa, respectively. Equal split ratio should be suggested to the charge and discharge CO2 to properly utilize the self-cycling cold energy.

Electrical transport properties of R1.9Cu9.2Sn2.8 compounds

Electrical transport properties of the R 1.9 Cu 9.2 Sn 2.8 (R = Y, Ce, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) compounds with the Dy 1.9 Cu 9.2 Sn 2.8 structure type (space group P 6 3 / mmc ) were studied. Polycrystalline samples were prepared by arc melting of the stoichiometric amounts of the constituent elements (nominal purities: rare earth metals − 99.9 wt. %, Cu − 99.99 wt. %, Sn − 99.999 wt. %) on a water-cooled copper hearth under a protective Ti-gettered argon atmosphere. Subsequently the buttons were annealed at 1 070 K for 720 h in evacuated silica tubes, followed by quenching in cold water. Quality of the prepared samples was tested by X-ray powder diffraction (diffractometer DRON-2.0M, Fe K α radiation) and Scanning Electron Microscopy (REMMA 102-02 electron microscope equipped with an energy-dispersive spectroscopy X-ray analyser). XRPD data were collected in the transmission mode on a STOE STADI P diffractometer (Cu K α 1 radiation). The temperature dependencies of electrical resistivity ( r ( T )) of R 1.9 Cu 9.2 Sn 2.8 stannides were measured employing two-probe method on millimeter-scale, well-shaped pieces cut by spark erosion from the polycrystalline samples in the temperature range 4.2-300 K (R = Ce, Gd, Tb, Dy, Ho, Er, Tm, Yb) and 11-300 K (R = Y, Sm, Lu). Electrical resistivity measurements showed that the resistivity values of the all studied compounds increase with temperature indicating metallic type of conductivity. For Y 1.9 Cu 9.2 Sn 2.8 and Lu 1.9 Cu 9.2 Sn 2.8 stannides, which contain nonmagnetic elements Y and Lu, the absence of transition on the r ( T ) dependences at low temperatures is consistent with the Pauli paramagnetism of compounds. The temperature dependence of the resistivity of Yb 1.9 Cu 9.2 Sn 2.8 compound is almost linear at high temperatures, at low temperature part there is a slight increase in resistivity, which is characteristic of Kondo systems. Change of the resistivity caused by magnetic ordering was not observed in the studied temperature interval for the R 1.9 Cu 9.2 Sn 2.8 compounds where R are Gd, Tb, Ho, Er. The slope change of the resistivity at low temperature part of r ( T ) dependencies for the R 1.9 Cu 9.2 Sn 2.8 compounds with R=Ce, Dy, Tm is associated with their magnetic ordering. Keywords : intermetallics, electrical resistivity, X-ray analysis, crystal structure.

Investigation of semiconductive Lu1-xScxNiSb solid solution

The electrokinetic and energetic characteristics of the semiconductor solid solution Lu 1- x Sc x NiSb were investigated in the ranges Т =80–400 K, х =0–0.10 . Samples were prepared using an electric arc furnace by direct arc melting of the constituent elements under a purified argon atmosphere (porous Ti was used as a getter). The alloys were annealed at 1 073 K for 720 hours and quenched in cold water. Phase analysis was performed using X-ray powder diffraction patterns of the synthesized samples. The elemental and phase compositions of the synthesized samples were examined by Scanning Electron Microscopy (SEM) using Tescan Vega 3 LMU scanning microscope. Microprobe analysis of the concentration of atoms on the surface of Lu 1- x Sc x NiSb samples, including x = 0–0.10, established their correspondence to the initial compositions of the alloys, and X-ray phase and structural analyzes showed no traces of extraneous phases on the diffractograms except for the main phase indexed in the MgAgAs structure type. The temperature dependencies of electrical resistivity ( r ( T )) were measured employing two-probe method on millimeter-scale, well-shaped pieces cut by spark erosion from the polycrystalline samples in the temperature range 80–400 K. Thermopower coefficient ( α ) was measured in relation to the pure copper in the temperature range 80–400 K. It has been experimentally established that in the Lu 1‑ x Sc x NiSb solid solution both structural defects of neutral and donor nature are simultaneously generated, the concentration of which increases with increasing content of Sc atoms. The observed high-temperature activation parts on the temperature dependences of the resistivity ln( ρ (1/ T )) for all Lu 1- x Sc x NiSb samples indicates the location of the Fermi level ε F in the band gap of the semiconductor, and positive values of the thermopower coefficient α ( T ) specify its position near the valence band. The main carriers of electric conductivity are free holes. From the high-temperature parts of the dependence α (1/ T ) the values of the activation energy ε 1 α are calculated, which are proportional to the amplitude of large-scale fluctuations of continuous energy bands. The calculated from the low-temperature parts values of activation energy ε 3 α are proportional to the modulation amplitude of small-scale fluctuations of strongly doped and compensated semiconductor. It was shown that the investigated semiconductor solid solution Lu 1- x Sc x NiSb is a promising thermoelectric material. Keywords : electric conductivity, thermopower coefficient, Fermi level, structural defect.

Apatite low-temperature chronometry and microstructures across a hydrothermally active fault zone

Low-temperature chronometers offer potential to gain insights into the temporal evolution of hydrothermal systems. The long-lived fault-bound Grimsel pass hydrothermal system (including a fossil and an active part) in the Central European Alps serves here as a key site to test such an application. Zircon and apatite grains were separated from samples collected along a fault transect. The resulting zircon (U-Th)/He ages are homogenous along the profile at 8–9 Ma and thus record the regional cooling evolution, remaining unaffected by the younger hydrothermal activity. In contrast, the apatite (U-Th)/He ages show three age groups: One Group (1) of ca. 5 Ma inside and outside the hydrothermal zone matches the low-temperature part of the regional cooling trend, while group (2) with ages as young as 1–2 Ma occurs in a central narrow zone associated with hydrothermal activity. One sample (group 3) displays older apparent ages compared to the regional cooling trend. Group (2) apatite samples reveal a different cathodoluminescence texture and trace-element chemistry, which we interpret together with the young age as apatite growth or re-crystallization within the hydrothermal system. Forward 1D modelling of He diffusion indicates that apatite (U-Th)/He ages should always be reset when exposed to hot thermal waters (up to ~140 °C) present over ka timescales or to intermediate temperature waters (~90 °C) over Ma timescales. Combining our measured apatite (U-Th)/He ages with forward modelling results highlight that, besides regional cooling trends, local heat anomalies within hydrothermal zones are very variable in space and time. Combined trace-element geochemistry and (U-Th)/He dating shows local occurrence of newly-formed apatites crystals, which are best described as geochronometers rather than thermochronometers. Such information is important to explore the longevity of hydrothermal systems and associated spatial distributions of heat anomalies.