Zone Melting Method Research Articles

Enhanced Weighted Mobility Induced High Thermoelectric Performance in Argyrodite Ag8SnSe6.

The argyrodite family has emerged as a promising thermoelectric candidate due to its highly diffusive Ag ions and inherent low thermal conductivity. To address issues that commonly arise with hot pressing (HP) sintering, this study proposes to use the zone melting (ZM) method to synthesize high-density polycrystalline bulk Ag8SnSe6 samples. The thermoelectric properties of samples synthesized by the ZM and HP methods were thoroughly evaluated over a temperature range of 300 to 700 K. Due to the weaker scattering of electrons, the ZM-synthesized samples exhibited an ∼60% increase in weighted mobility, compared to those produced by the HP method. Despite the slight increase in thermal conductivity, the specimen synthesized by the ZM method achieves a higher peak zT value of 1.05 at 700 K. The average zT value also improves to 0.71 across the temperature range of 300 to 700 K. This work demonstrates the effectiveness of the ZM method in enhancing the thermoelectric performance of Ag8SnSe6, with great potential applicability to other argyrodite compounds.

Preparation of In0.5Sn0.5Se Crystal via a Zone Melting Method and Evaluation of its Thermoelectric Properties

AbstractIndium selenides (InSe) is a promising layer‐structured semiconductor with broad potential applications in photovoltaics, diodes, and optic devices, but its thermoelectric performance is limited by the high thermal conductivity. In this work, by alloying high‐performance thermoelectric SnSe in InSe, the In0.5Sn0.5Se crystal is prepared via a zone melting method. The density of In0.5Sn0.5Se crystal is measured as 5.81 g cm−3 which is between the density of pure SnSe and InSe. The XRD measurements indicate that the grown In0.5Sn0.5Se crystal consists of InSe and SnSe crystals with a preferred orientation along (00l) and (h00) planes, respectively. SEM and EDS analysis reveal that eutectic InSe and SnSe phases interdigitate with each other. The thermogravimetry analysis shows a slow decrease at a temperature ≈700 °C. In0.5Sn0.5Se crystal displays a n‐type conduct behavior, the electrical conductivity σ is ≈0.02 Scm−1 at room temperature and increases to 8.4 Scm−1 under 820 K. The highest power factor PF is estimated to be ≈0.36 µWcmK−2 near 570 K. The InSe‐SnSe phase boundaries lead the thermal conductivity of In0.5Sn0.5Se crystal to be as low as 0.29 Wm−1K−1. Due to the low lattice thermal conductivity, In0.5Sn0.5Se crystal shows a ZT value of 0.04 at 600 K in this work.

Ice zone melting method for probing ion-specific partitioning at frozen interface

When water freezes, impurities are expelled from the ice crystals and accumulate in the grain boundary space. Salts are a major impurity common to aqueous systems and, upon freezing, are dissolved in the liquid phase at temperatures above the eutectic point. Some constituent ions remain near the ice interface, but some readily diffuse away from the interface. The behavior of ions depends on their properties and affects the progress of freezing. Therefore, although the equilibrium and dynamic behavior of ions at this interface is important for understanding water freezing, nothing is known because of the lack of a suitable approach to this aspect. We extend zone melting, which is used for the purification of metal and semiconductor materials, to frozen aqueous systems. The partition behaviors of anions (F−, Cl−, Br−, and NO3−) between frozen and thawed zones are evaluated using ice zone melting followed by ion chromatographic determination of ions. The effective partition coefficients of the ions are determined from the zone melting measurements of frozen aqueous solution. Differences in the effective partition coefficient between anions are observed. The ratios for anions reveal the ion-specific behaviors at the interface between the freeze concentrated solution (FCS) and melting zone. Poorly hydrated ions tend to be thermodynamically distributed well in the FCS. However, as zone melting proceeds, F− shows a different trend from that predicted by ion hydration. This characteristic behavior of F− is understood by considering its lower diffusivity than other halide anions. Thus, ice zone melting provides information on the equilibrium and dynamic features of ions at the frozen aqueous interface.

Investigation and optimisation of a lithium-drift silicon detector using Si–Li structure and bidirectional diffusion and drift techniques

Abstract The research relevance is predefined by the continuous development and improvement of radiation analysis methods and the need for more efficient and accurate detectors for various applications. This research may improve the sensitivity and resolution of Si(Li) detectors, which is important for scientific and industrial research as well as radiation safety monitoring. The research aims to analyse and improve the performance of a Si(Li) lithium-drift silicon detector. The methods used include an analytical method, classification method, functional method, statistical method, synthesis method and others. The results of the two-sided observation of lithium diffusion in silicon monocrystals provided valuable information about the characteristics of the process and its dependence on the method of silicon production. A large-diameter detector detection mode was found to be important for optimising the production of such detectors. The diffusion process in monocrystalline silicon produced by the shadowless zone melting method is relatively fast. This means that lithium ions penetrate the material rapidly and spread evenly throughout its volume. This fast diffusion process can be useful for detectors that need to respond quickly to incoming signals. It was found that in monocrystalline silicon produced by the Czochralski method, there is a delayed penetration of lithium ions.

Growth and Characterization of Large-size InSe Crystal from Non-stoichiometric Solution via a Zone Melting Method

Growth and Characterization of Large-size InSe Crystal from Non-stoichiometric Solution <i>via</i> a Zone Melting Method

Effects of Er3+ and Yb3+ concentrations on upconversion luminescence and thermal sensing characteristics of Sc2O3:Er3+/Yb3+ phosphors

Sc2O3:Er3+(x mol%)/Yb3+(3 mol%) (x = 0.3, 0.5, 0.7) and Sc2O3:Er3+(0.5 mol%)/Yb3+(y mol%) (y = 1, 3, 5) phosphors were synthesized by CO2 laser zone-melting method. The upconversion luminescence (UCL) spectra of Sc2O3:Er3+/Yb3+ fluorescent materials, which were pumped by 980 nm, were measured and analyzed. The results show that the UCL intensity reaches maxima when doped with 0.5 mol% Er3+ and 3 mol% Yb3+, and the increase of Yb3+ concentration leads to reduce the ratio of green UCL to red UCL. The temperature-dependent UCL spectra of Sc2O3:Er3+/Yb3+ fluorescent materials with various Er3+ and Yb3+ concentrations were measured from 290 K to 1023 K, and the thermal sensing characteristics were revealed via the fluorescence intensity ratio (FIR) technique. The maximal relative sensitivity (SR) are almost independent of the Er3+ and Yb3+ concentration, while the maximal absolute sensitivity (SA) increases with Yb3+ concentration in the whole measurement range. Among the prepared samples, the maxima of SA and SR are achieved for the sample of Sc2O3:Er3+(0.5 mol%)/Yb3+(5 mol%)，with the values of 5.34 × 10−3 K−1 (364.1 K) and 12.5 × 10−3 K−1 (290 K), respectively. Interestingly, for Sc2O3:Er3+ (0.5 mol%)/Yb3+ (3 mol%), having the highest UCL intensity, its maximum SA and SR are 4.90 × 10−3 K−1 (371.4 K) and 11.2 × 10−3 K−1 (290 K). The wide temperature sensing range and relatively high sensitivities of the fabricated materials provide excellent potential for temperature sensing.

Niobium monoxide NbO single crystal growing by floating zone method

In this work, a single crystal of niobium monoxide NbO was grown by crucible-free zone melting method. Polycrystalline NbO with ordered cubic structure (sp.gr. Pm-3m) with vacancies in both metal and nonmetal sublattices served as an initial material. According to XRD data, the grown niobium monoxide NbO single crystal has predominant growth in the [111]B1 direction and contains only one ordered cubic phase NbO, its lattice constant is equal to a = 421.2 pm. The growing mechanism of the NbO single crystal was clarified, in accordance with the Kossel and Stransky theory, it was suggested that the single crystal grows layer by layer. Analysis of the Kikuchi lines geometry allowed the orientations and disorientations of single crystal to be determined to high precision. An analysis of the diffraction pattern and intersection of Kikuchi lines showed that the NbO single crystal has (111)B1 facet. The experimental Laue diffraction patterns confirmed this direction of niobium monoxide NbO single crystal growth.

Microstructure and mechanical properties of ZrO2 fiber toughened Al2O3/ZrO2(Y2O3) solidified ceramics prepared with high frequency induction zone melting

ZrO2 fiber toughened and non-fiber toughened Al2O3/ZrO2(Y2O3) directionally solidified eutectic ceramics (DSECs) were prepared via high frequency induction zone melting method, and the effects of both the fibers and the growth rate on the microstructure and mechanical properties were investigated. The results showed that both the fiber toughened and the non-fiber toughened DSECs were composed of α-Al2O3, c-ZrO2 and m-ZrO2, and their microstructures were all typical colony structure. The phase spacing in intracolony (λ) for these two kinds of DSECs gradually decreased with the increase of growth rate (ν), they satisfied λ = 10.31ν−1/2 and λ = 13.65 v−1/2, respectively. And the minimum values of λ were 2.33 ± 0.25 µm and 2.99 ± 0.17 µm, respectively, i.e., that is ZrO2 fiber decreased the phase spacing in intracolony about 22%. The fracture toughness for these two DSECs increased continuously with the growth rate, reached the maximum values of 5.72 ± 0.20 MPa m1/2 and 3.95 ± 0.23 MPa m1/2 at 30 mm/h, respectively, i.e., the former was about 1.45 times of the latter. At the same growth rate, the fracture toughness of ZrO2 fiber toughened DSEC were obviously higher than those of DSEC without fiber. When they encounter fibers with high elastic modulus during their propagation, the cracks will undergo deflection, bifurcation, or bridging, and the fibers will undergo debonding and pulling-out under the external stress, both of which consume a large amount of crack propagation energy and achieve toughening effect.

Scrap Recovery of n‐Type Bismuth Telluride Ingot by Second Zone Melting and PbBr2 Doping

Bismuth telluride is the only commercially applied thermoelectric material. The n‐type material is usually prepared by the method of zone melting; however, the utilization ratio of the ingot is relatively low, owing to the bad thermoelectric performance of the two ends. Herein, the waste of n‐type bismuth telluride is recovered by the second zone melting and PbBr2 doping. It is shown that the second zone melting can improve the grain alignment, leading to the increase of carrier mobility. When PbBr2 doping is introduced, lattice thermal conductivity is largely reduced by the high dense dislocations. As a result, the peak power factor and maximum ZT reach 53 μW cm−1 K−2 and 1.15, respectively, which are even higher than the values of the original commercial material. This work provides an economic and applicable strategy to recover the waste of bismuth telluride thermoelectric materials.

Impacts of Ce3+ doping on temperature sensing characteristics of LuAG: Yb3+/Ho3+ up-conversion fluorescent materials

A series of LuAG: 5 mol%Yb3+/0.5 mol%Ho3+/x mol%Ce3+ (x = 0, 0.2, 0.5, 1.0, 2.0) up-conversion (UC) fluorescent materials were prepared using CO2 laser heating zone melting method. The X-ray diffraction (XRD) patterns confirm that the prepared samples have a pure LuAG crystal phase. Under excitation of a 980 nm laser, the up-conversion luminescence (UCL) spectra of the prepared samples were obtained. Two UCL emission bands of Ho3+ ions were observed, including green emission band of the 5F4/5S2→5I8 transition, and red emission band of the 5F5→5I8 transition. Due to the cross-relaxation (CR) processes between Ce3+ ions and Ho3+ ions, the doping of Ce3+ ions can effectively improve the UCL efficiency of Ho3+ ions, and the emission intensity reaches maximum when doped with 1 mol% Ce3+. The temperature sensing characteristics of LuAG: Yb3+/Ho3+ and LuAG: Yb3+/Ho3+/Ce3+ from 303 K to 723 K were studied by fluorescence intensity ratio (FIR) method. By doping 1 mol% Ce3+ ions, the absolute sensitivity of the sample has been significantly improved, with the maximal absolute sensitivity of 0.0951 K−1 (303 K), and the maximal relative sensitivity of 0.0103 K−1 (343 K). The high sensitivity and wide measurement range make LuAG: Yb3+/Ho3+/Ce3+ UCL material ideal for temperature sensing.

Crystalline-face-dependent photoelectrochemical properties of single crystalline CuGaSe2 photocathodes for hydrogen evolution under sunlight radiation

Photoelectrochemical (PEC) water splitting by using a electrode based on a single crystalline compound provide a good opportunity for studying on fundamental aspects of net semiconductor bulk properties related to PEC performance. In this study, single crystalline CuGaSe2 wafers exposed (321), (312), and (112) facets were used as sources of photocathodes for investigating PEC properties for water reduction into hydrogen under sunlight radiation related to their surface properties. A CuGaSe2 single crystalline ingot grown by using the zone melting method was cut along with different directions to obtain wafers with different crystal orientations. The electrical and electron-energy properties of wafers after annealing in an Se atmosphere indicated the formation of a Cu-deficient component on their surfaces when the wafers oriented (321) and (312) directions were used, whereas formation of a component was not observed on the wafer oriented in the (112) direction. Since the Cu-deficient component acted as a hole blocking layer to suppress the recombination of photoexcited carries at the heterojunction, photocathodes based on wafers having (321) and (312) orientations showed enhanced PEC performance for water reduction compared to the PEC performance of a photocathode based on a wafer having the (112) orientation. Highly active photocathodes for water reduction based on polycrystalline thin films usually have preferential (112) orientation, whereas those of densely packed powder forms would not be probable for controlling crystalline orientations. Therefore, present results would be a guide to achieve further improvements of PEC water reduction using such conventional systems.

Comprehensive microstructure regularization mechanism and microstructure–property stability at 1773 K of directionally solidified Al2O3/GdAlO3 eutectic ceramic composite

Melt grown Al2O3/GdAlO3(GAP) eutectic ceramic composite is considered as a promising ultra–high temperature structural material in fields as aerospace, power generation and so on. In order to tune the properties of directionally solidified Al2O3/GAP eutectic ceramic composite, its microstructure evolution is investigated over a wide range of compositions and solidification rates by laser floating zone melting method (LFZM). With the increase of solidification rate and the enrichment of Al2O3 phase, the eutectic microstructure undergoes a transformation from “Chinese script” irregular morphology to rod–like regular and complex regular morphology. The synergistic effects of composition and solidification rate on the microstructure regularization have been quantitatively characterized by the proportion of regular eutectic. High solidification rate (>200 μm/s) is beneficial to the formation of isothermal interface, partly inhibiting the anisotropic growth of Al2O3 faceted phase, which further promotes the coupling growth of the eutectic phases at the front of the interface and facilitates the microstructure regularization. The stability of eutectic spacing is verified to coincide with the Ostwald ripening relationship when the eutectic ceramic composite is thermally exposed at 1773 K for long–term (250 h). The microstructure coarsening rate is less than 0.003 μm/h, and the hardness slightly decreases about 4%, and the fracture toughness remains almost unchanged, which indicates excellent thermal stability of microstructure and property for the Al2O3/GAP eutectic ceramic composite at high temperature.

Synergistic effects improve thermoelectric properties of zone-melted n-type Bi2Te2.7Se0.3

Bismuth telluride (Bi2Te3) is the commercially used thermoelectric material near room temperature, and the widely-adopted zone-melting method is suitable for mass production. However, the ZT value of commercial n-type Bi2Te3 is still maintained around 1.0 and severely restrict the further development of thermoelectric applications. In this work, the thermoelectric property of zone-melted n-type Bi2Te2.7Se0.3 material is significantly improved by the synergistical effects of the BiI3 and SnSb2Te4 co-doping. The non-toxic and non-hygroscopic BiI3 is proved to be an effective electron dopant for the n-type Bi2Te2.7Se0.3, leading to the significantly enhanced power factor and partially suppressed bipolar effect. The SnSb2Te4 doping further induces new scattering centers for heat-carrying phonons and results in a relatively low lattice thermal conductivity of 0.72 W m−1 K−1 at 300 K. Consequently, a ZTmax of 1.30 at 325 K and a ZTave (300–500 K) of 1.00 are achieved in the Bi2Te2.7Se0.3 + 0.15 wt% BiI3 + 0.15 wt% SnSb2Te4 sample. This work provides a feasible way to effectively improve the thermoelectric performance of n-type zone-melted Bi2Te3.

Growth and characterization of InBi0.95Te0.05 and InBi0.90Te0.10 crystals

Indium bismuthide is a well-known III-V group semi metallic compound. The compositions used were InBi0.95Te0.05 and InBi0.90Te0.10 crystals. The zone melting method used to grow the crystals. The zone-melting furnace has shown a temperature gradient of 45 °C/cm, and it has yielded the good quality crystals obtained, having a growth rate of 0.3 cm/h. The characterization of crystals was carried out using powdered X-ray technique. Using the FTIR spectra, the direct type band gap has been evaluated. The thermoelectric power measurement was carried out for InBi0.95Te0.05 and InBi0.90Te0.10 crystals. The Van der Pauw method has been employed for the Hall measurements at room temperature. This work report the detailed results of the above mentioned study and conclusions drawn therein.

Features of bismuth telluride based ternary alloys for thermoelectric applications

The presented article provides a comparative analysis of the methods of manufacturing technology for semiconductor branches of p- and n-type conductivity. For comparative analysis, a method is considered for obtaining ternary alloys based on the Bi2Te3 base material by pressing and zone melting. The sequence of the manufacturing process, the principles of operation and design of devices used to obtain alloyed substances, as well as methods for studying and measuring the electrophysical parameters of the thermoelement legs included in the assembled thermopile are described. The principles of automatic temperature control of an electric furnace by a two-position method are indicated. The advantages of the zone melting method are determined and the best values of the figure of merit of a thermoelectric material are shown. It is proved that the original values of the parameters of the branches are preserved after they are assembled into a battery.

On real-time control of microstructure of TiAl specimens with varied cross-sections based on numerical calculation and machine learning

In our previous study, TiAl alloys with varied cross-sections were prepared via the electromagnetic cold crucible zone melting (ECCZM) method. However, due to the unstable temperature field, the equiaxed grain region appeared in the columnar grain, disrupting the microstructure continuity. Herein, the processing method was redesigned based on numerical calculation and machine learning (ML). Real-time adjusted processing parameters were established to stabilize the temperature field. Firstly, the equation of absorbed heating power about withdrawing distance was calculated based on the magnetic field distribution in the cold crucible, and the input power was adjusted in real-time accordingly. Subsequently, a combination of real-time adjusted input power and withdrawing rate was established based on the balance of absorbed heating power and heat loss in the mushy zone. The specimen with real-time adjusted input power and withdrawing rate was also prepared. In addition, the matched input power and withdrawing rate were optimized by ML, and the TiAl alloy without equiaxed grain was obtained via the new processing method. Microstructure and mechanical properties of the directionally solidified TiAl alloy with the conventional ECCZM method (CM) and the real-time adjusted (RA) method were compared. It was found that equiaxed grains would induce intergranular fracture. The ML-optimized RA method can eliminate equiaxed grain and obviate the occurrence of intergranular fracture during tensile deformation, thus preventing early fracture and improving the tensile strength.

Study on the behavior of impurities in zone melting of aluminum

In this study, the migration and distribution behaviors of Cu, Si, Fe, and Ti impurities in the process of preparing high-purity Al by zone melting under an argon atmosphere were investigated. The width of the molten zone during the experiment was determined as 40 mm, based on simulation calculation results. The influences of the travel speed of the molten area and number of zone melting times on the migration and distribution of the Cu, Si, Fe, and Ti impurities in the Al were experimentally demonstrated. The contents of the impurities Cu, Si, Fe, and Ti in the middle of the sample (i.e., 140 mm from the head end) were 0.9057, 0.8116, 0.1202, and 0.4237 ppm, respectively, when the travel speed of the molten area was 1.0 mm/min and with 15 times of zone melting. The contents of all the above impurities were reduced to the requirements of Chinese national standard and 99.9995% (i.e., 5N5) high-purity Al was obtained from 4 N Al by the zone melting method under the above optimal experimental conditions. The experimental results show that the effect of the number of zone melting times on the removal of the Cu, Si, and Fe impurities is more evident, and that these impurities are easier to separate than Ti. Therefore, high-purity Al with lower Cu, Si, and Fe contents can be obtained by optimizing the travel speed of the molten area and number of zone melting times.

Effects of Yb3+ concentration on up-conversion luminescence and temperature sensing characteristics of Tm3+/Yb3+:Y2O3 phosphors

Y2O3:0.5 mol%Tm3+/x mol%Yb3+(x = 3, 5, 7, 10) luminescent materials have been synthesized by the CO2 laser zone melting method. With 980 nm excitation, the up-conversion luminescence (UCL) emission bands corresponding to 1G4→3H6, 1G4→3F4, 3F2,3→3H6, and 3H4→3H6 transitions of Tm3+ ions were obtained in visible and near-infrared spectral regions, among which the luminescence emitted by 1G4→3H6, 3H4→3H6 transitions shows obvious Stark splitting. Besides, the optimal doping concentration of Yb3+ is 5 mol%. The up-conversion luminescence spectra of Y2O3:0.5 mol%Tm3+/5 mol%Yb3+ were recorded from 224 K to 873 K. The temperature sensing properties of 3F2,3 and 3H4, 1G4(a) and 1G4(b) energy levels of Tm3+ ions were investigated by the luminescence intensity ratio (LIR) method in a wide temperature range, and the possibility of using 3H4(a), 3H4(b) thermally coupled levels (TCLs) of Tm3+ ions for temperature sensing was developed. The results show that 1G4(a) and 1G4(b), 3F2,3 and 3H4, 3H4(a) and 3H4(b) of Tm3+ ions are TCLs, and the Stark sub-levels own relatively high absolute sensitivity at low temperature, whereas the 3F2,3 and 3H4 TCLs of Tm3+ ions are more suitable for high temperature measurement. The results show that the Tm3+/Yb3+:Y2O3 luminescent material can be a promising candidate for temperature sensing.

Growth of ZnTe Semiconductor Crystal Via a Te Flux Zone Melting Method and Characterization of Its Properties

AbstractIn this work, a kind of II;‐VI group ZnTe semiconductor crystal is successfully grown using a Te flux zone melting method from Zn: Te = 3: 7 mole ratio solution. The crystal has standard F43m cubic space group and the a/b/c lattice constants are all calculated to be 6.105 Å. Energy dispersive spectroscopy analysis confirms it has quasistoichiometric ratio and the Zn/Te elements are distributed in the material homogeneously. The polished 1.0 mm thickness (110) wafer exhibits a highest ≈64.5% transmittance near 2400 nm wavelength and the bandgap Eg is deduced as 2.223 eV. ZnTe crystal shows a heavy volatilization start from 910 °C and the weight losing speed is about ≈1.45% min−1. The thermal conductivity k displays good repeatability in the cooling and heating stages, the k value is about 15.8 Wm−1 K−1 at room temperature and is deceased to 3.53 Wm−1 K−1 under 500 °C. These results would be of great reference when ZnTe crystal is used for device design and application in the future.

Ultra-fast fabrication of Bi2Te3 based thermoelectric materials by flash-sintering at room temperature combining with spark plasma sintering

Highly crystalline Bi2Te3 based compounds with small grain size were successfully synthesized by flash sintering (FS) method in 10 s at room temperature under suitable current density using Bi, Te and Se powders. The instantaneously generated local Joule heat at grain boundary is regarded as the main reason for the rapid completion of chemical reaction and crystallization. By combining FS synthesis method with spark plasma sintering (SPS), Bi2Te3 based bulk materials with high relative density were fabricated in 10 min. Suitably prolonging sintering temperature and holding time in SPS process can decrease carrier concentration and phonon thermal conductivity, while increasing carrier mobility. Hence, the sample prepared at 753 K for 3 min shows 20% higher ZT value than that of the sample prepared at 723 K for 3 min. Compared with common zone melting or powder metallurgy methods taking several hours by complex operation, this method is time-saving and low cost.