High Pressure And High Temperature Method Research Articles

S-filled and Te-doped CoSb3 materials prepared by HPHT method with ultra-low thermal conductivity

In this paper, a series of S[Formula: see text]Co4Sb[Formula: see text]Te[Formula: see text] samples were prepared by high pressure and high temperature (HPHT) method under different pressures. The synthesis time was shortened from several days to 0.5 h. Te doping and S filling simultaneously optimized the thermal and electrical transport properties of the CoSb3 materials. We found a porous architecture containing rich grain boundaries, different grain sizes, nano- to micrometer-sized pores, and a large number of dislocations, which can scatter a wide spectrum of phonons. Seebeck coefficient [Formula: see text], electrical resistivity [Formula: see text], and thermal conductivity [Formula: see text] were measured between 295 K and 773 K. The minimum thermal conductivity of S[Formula: see text]Co4Sb[Formula: see text]Te[Formula: see text] synthesized at 3.0 GPa was 1.23 Wm[Formula: see text] K[Formula: see text], and its maximum zT value reached 1.07 at 773 K, especially the lattice thermal conductivity was as low as 0.49 Wm[Formula: see text] K[Formula: see text].

Enhancing the fracture toughness of polycrystalline diamond by adjusting the transgranular fracture and intergranular fracture modes

Enhancing the fracture toughness of polycrystalline diamond (PCD) is challenging because of its inherent brittleness and the absence of a toughness mechanism. Elucidating the transgranular fracture (TF) and intergranular fracture (IF) modes in PCD is urgent for fabricating robust PCDs. In this study, the toughness of PCD was optimised by adjusting the IF and TF modes. The high pressure and high temperature method (HPHT) was used to fabricate PCDs with different grain sizes (nano- to micro-scale) to modulate the IF and TF modes. The results indicate that a mixture of the IF and TF modes yields an optimum toughness in PCD compared to the single fracture mode, which yielded a high hardness (114.6 GPa) and high toughness (13.0 MPa∙m0.5). The toughness was approximately three times that of single-crystal diamonds (SCDs) and comparable to that of pure nanotwinned diamonds (NtDs). The mixed modes induce a toughening mechanism of high frequency large crack deflection, crack bridging, pull-out, and crack branching, which increases the toughness of the PCD. This work provides new insights into optimising the toughness of PCD, which is significant for fabricating robust PCDs for future applications.

Optimization of thermoelectric properties in elemental tellurium via high pressure

High pressure and high temperature (HPHT) technology, as an extreme physical condition, plays an important role in regulating the properties of materials, having the advantages of enhancing doping efficiency, refining grain size, and manufacturing defects, therefore it is quite necessary to study the effectiveness on tuning thermoelectric properties. Elemental telluride, a potential candidate for thermoelectric materials, has the poor doping efficiency and high resistivity, which become an obstacle for practical applications. Here, we report the realization of a dual optimization of electrical behaviors and thermal conductivity through HPHT method combining with the introduction of black phosphorus. The results show the maximum zT of 0.65 and an average zT of 0.42 (300 K–610 K), which are increased by 55% and 68% in the synthesis pressure regulation system, respectively. This study clarifies that the HPHT method has significant advantages in modulating the thermoelectric parameters, providing a reference for seeking high performance thermoelectric materials.

High-pressure and high-temperature synthesis of stable SxCo3.6Ni0.4Sb12 skutterudite compounds

Compared to Te, Ni is found in abundance in the earth's crust. At the same time, the mechanical properties of Ni atom-substituted skutterudite are significantly improved. In this study, a series of S-filled Ni-substituted skutterudite compounds were synthesized by a high-pressure and high-temperature (HPHT) method in the synthesis pressure range of 1.0–3.0 GPa. The phase composition, microscopic morphology, and electrothermal transmission properties of the SxCo3.6Ni0.4Sb12 (x = 0, 0.05, 0.10, 0.20) samples were systematically characterized. Phase composition analysis showed that the introduction of S atoms into the intrinsic pores of skutterudite can improve the solid solution limit of Ni atoms in the Co sites of skutterudite. The filling limit of S increased with the synthetic pressure. Moreover, microscopic morphology analysis revealed that the filling of S atoms inhibited the growth of grains. A large number of lattice fringes in different directions were found in the sample, containing abundant microstructures such as lattice distortions and dislocation defects. Compared with the synthesized samples, S0.05Co3.6Ni0.4Sb12 synthesized at 1.0 GPa had a maximum room temperature power factor of 7.98 × 10−4 Wm−1K−2. The electrical properties of S0.05Co3.6Ni0.4Sb12 samples stored for 6 months without any protective measures were tested at room temperature. No obvious changes in performance were observed, which proved that the HPHT method can synthesize stable samples. After several thermal cycles, the electrical properties of the S0.05Co3.6Ni0.4Sb12 sample was tested for variable temperature, and it was found that the sample still had good stability. How the substitution of S atoms with Ni atoms reduces the lattice thermal conductivity can be explained by fitting the Callaway model. The S0.05Co3.6Ni0.4Sb12 sample synthesized at 1.0 GPa had a maximum zT value of 0.46 at the test temperature of 773 K, which decreased to 0.43 after multiple thermal cycles at the same temperature.

Enhanced thermoelectric performance based on special micro-configuration of graphene-ZnO induced by high-pressure and high-temperature

Zinc oxide (ZnO) is a promising high-temperature thermoelectric material. Graphene is typically a two-dimensional material, and its development and application have attracted wide attention due to its excellent thermal stability and mechanical properties. To the best of our knowledge, the graphene-ZnO (C–ZnO) composite has never been studied in the field of thermoelectric conversion. The high-pressure and high-temperature (HPHT) technique has unique advantages in improving the thermoelectric properties of ZnO. In this study, for the first time, C–ZnO bulk energy materials with novel micro-configuration were prepared by rapid sintering using the HPHT method. Observation under a microscope revealed that as the doping amount of graphene increased, a large number of graphene nanowires formed connected between the ZnO grains, and with the excess amount of graphene introduced the morphology of the ZnO grains changed and their size became smaller. This novel micro-configuration of the 0.1C–ZnO sample showed an ultrahigh electrical conductivity of 2.8 × 104 S/m with a significantly lower lattice thermal conductivity of 4.3 Wm−1K−1 at 973 K. Ultimately, at 973 K, the zT value of the 0.1C–ZnO sample was 129 times higher than that of pure ZnO. Therefore, the high-temperature thermoelectric material C–ZnO prepared by the HPHT method can be used in automobile exhaust systems and industrial boilers to effectively recover and reuse the waste heat.

Rapid preparation and characterization of pyrite materials under HPHT: A new method

This paper reports the synthesis of bulk pyrite (FeS2) polycrystals at high pressure and high temperature (HPHT) for the first time. The HPHT method markedly improves the speed of synthesis, reducing the time for synthesizing bulk pyrite from several hundred hours to several hours. A unique honeycomb-type structure was introduced into the system by the primary reaction to refine the size of the reactants. On this basis, the sulfur-deficient contamination phase Fe7S8 was effectively eliminated by secondary synthesis. Using Raman spectroscopy and X-ray diffraction (XRD), the crystalline phase of the product was confirmed to be the cubic pyrite phase. The crystal structure and initial crystal parameters of pyrite crystals synthesized under HPHT conditions were obtained for the first time by Rietveld refinement with GASA software. In combination with a scanning electron microscope (SEM) assay, the reaction process was traced, and the significance of secondary synthesis for HPHT was analyzed. Seebeck data showed that as the temperature increased, the sample changed from p-type to an n-type semiconductor and the conductivity increased monotonically, revealing the typical semiconductor characteristics of pyrite. UV reflectance spectra and VSM tests revealed the bandgap width and magnetic properties of pyrite.

共焦点ラマン分光法を用いたc-BN含有単結晶ダイヤモンド粒子の結晶性分析とTEM-EELS分析によるヘテロ界面の検討

Several theories have been proposed to synthesize diamond particles from graphite using a metal solvent（also called a catalyst, flux or dissolver）under high-pressure and high-temperature（HPHT）conditions. Many researchers support the “dissolution-precipitation” theory, by which graphitic carbon dissolves in molten metal and subsequently precipitates in diamond form. An alternative is Hosomi's theory: solid state nucleation occurs to form diamond crystals. This study uses confocal Raman spectroscopy to examine the crystallinity of cubic boron nitride （c-BN）contained in a single-crystal diamond matrix synthesized using HPHT method according to Hosomi's theory. We also observed theheterointerface between c-BN and the diamond matrix using transmission electron microscopy to assess the type of bonding present. Constituent elements and the local chemical bonding state were examined using electron energy loss spectroscopy. Results demonstrated that the c-BN and diamond were not bonded directly, but revealed an approx. 5-nm-thick boron-based compound（or amorphous）layer at the interface. The respective concentrations of boron in diamond and carbon in c-BN were below the detection limits, indicating no effect on the crystallinity of either material under the HPHT conditions.

Micromorphology and energy spectrum analysis of AsSe prepared by high-pressure and high-temperature

Polycrystal compound AsSe was prepared rapidly by high pressure and high temperature (HPHT) method under the condition of 2.5GPa and 950K. The phase analysis, SEM and EDS of the samples were carried out. The results show that AsSe compound samples with fine crystallinity can be prepared rapidly by HPHT method, and the grain diameter of the samples is about 20 μ m. The results of AsSe EDS analysis show that the atomic ratio of the compound is close to 1:1.

Synthesis diamond grains containing cubic boron nitride using HPHT catalysts powder method

Synthesised diamond are used in a wide range of industrial applications that exploit the property of diamond as the hardest material, including processing tools for the purposes of cutting, grinding, and polishing. Industrial diamonds are typically synthesised by the high-pressure and high-temperature (HPHT) method. It is needless to say that the crystalline properties of the diamond itself are essential for industrially used diamond abrasive grains. However, a comprehensive range of functionalities, including shape, self-sharpening ability, and hardness are key factors for the adoption of diamonds as abrasives. Diamonds synthesised by the HPHT method contain the raw catalyst trapped inside their grains. When utilizing this characteristic of synthesis diamonds positively, It can be possible to synthesis diamond composite abrasive grains with other solid substances introduced into the diamond crystals. In this article, we report the synthesis of novel industrial diamond grains that are composite abrasives. By introducing cubic boron nitride (cBN) as a raw material, we synthesised diamonds containing cBN.

Gemologic and Spectroscopy Properties of Chinese High-Pressure High-Temperature Synthetic Diamond

Compared with the chemical vapor deposition method, the high-pressure and high-temperature (HPHT) method has some advantages, such as fast diamond crystal growth speed, mature technology and easy mass production. HPHT method synthetic diamond is widely used industrially, but gem-quality synthetic diamond from China has rarely been reported. In this work, the gem-quality diamond synthesized by State Key Laboratory of Superhard Materials, Jilin University, China (SKLSHM), using the cubic hinge press equipment by the HPHT method, was investigated by microscopy, field-emission scanning electron microscopy (FE-SEM) and Diamond View observations as well as infrared spectrometer, ultraviolet–visible spectrometer (UV spectrometer) and energy-dispersive x-ray fluorescence tests. FE-SEM observation showed that regular growth steps and obvious growth pits were common on the {100} surface, and they were consistent with the distribution of internal metal inclusions. In most cases, the {111} plane is significantly flatter than the {100} plane, which may be related to the surface atomic state. It also can be seen that the internal metal inclusions are easily aligned along the internal growth boundary,which may be due to the different growth rates of different crystal faces during diamond growth. The fluorescent image under Diamond View shows the special geometric growth zone structure. Cubes, octahedrons and rhombohedral dodecahedrons have different intensities of orange, yellow, blue and other uneven fluorescences, which can be used as the most important diagnostic evidence.

Pressure induced convergence of conduction bands in Al doped Mg2Si: Experiment and theory

High-pressure and high-temperature (HPHT) synthesis provides an effective way to tune the band structure of materials and improve their electronic properties. To investigate the influence of synthesis pressure on electronic properties, Mg1.97Al0.03Si samples were synthesized using the HPHT method. The maximum effective mass 0.92me is obtained for the sample prepared with the synthesis pressure of 3 GPa, leading to the biggest Seebeck coefficient −201.3 μV/K at room temperature. Meanwhile, the 3 GPa sample obtains the higher electron carrier concentration and electrical conductivity, resulting in nearly overall enhancement of power factor. The Density Functional Theory (DFT) calculations evidences that the Conduction Bands Minimum (CBM) can be tuned effectively by applied pressure and the convergence of the CBM leads to a larger effective mass of DOS, which are beneficial to the enhancement of power factors. These results indicate that high-pressure is a powerful tool to tune Mg1.97Al0.03Si band structures.

Synthesis and characterization of NaAlSi2O6 jadeite under 3.5 GPa**Project supported by the National Natural Science Foundation of China (Grant Nos. 51172089 and 51171070) and the Graduate Innovation Fund of Jilin University, China (Grant No. 2016065)

The high pressure and high temperature (HPHT) method is successfully used to synthesize jadeite in a temperature range of 1000 °C–1400 °C under a pressure of 3.5 GPa. The initial raw materials are Na2SiO3 9H2O and Al2(SiO3)3. Through the HPHT method, the amorphous glass material is entirely converted into crystalline jadeite. We can obtain the good-quality jadeite by optimizing the reaction pressure and temperature. The measurements of x-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) and Raman scattering indicate that the properties of synthesized jadeite at 1260 °C under 3.5 GPa are extremely similar to those of the natural jadeite. What is more, the results will be valuable for understanding the formation process of natural jadeite. This work also reveals the mechanism for metamorphism of magma in the earth.

Quaternary thermoelectric materials: Synthesis, microstructure and thermoelectric properties of the (Bi,Sb)2(Te,Se)3 alloys

Abstract High-quality quaternary Bi 0.5 Sb 1.5 Te 3−x Se x (BSTS) alloys with x = 0.3, 0.5 and 0.75 are successfully synthesized in 25 min by high pressure and high temperature (HPHT) method. Due to the effects of synthesis pressure and Se doping, the texture and microstructure exhibit abundant distorted layers and lattice defects. The unique triangular nanoplates can be obtained in the microstructures by HPHT method without any substrates, suggesting that Bi 0.5 Sb 1.5 Te 3−x Se x has a nature of the epitaxial growth. The thermoelectric transport properties are characterized in detail, revealing an evident correlation with the amount of Se doping. As a result, a maximum ZT value of 0.95 is achieved at 503 K from the as-prepared Bi 0.5 Sb 1.5 Te 2.7 Se 0.3 alloys. Additionally, Raman spectra are conducted and then indicate that Se doping contents have an important influence on the lattice vibrations and lattice structures of quaternary (Bi,Sb) 2 (Te,Se) 3 alloys.

Electrical transport and thermoelectric properties of PbTe1−xIx synthesized by high pressure and high temperature

N-type thermoelectric materials PbTe doped with iodine (PbTe1−xIx, x = 0.0001, 0.0003, 0.0007 and 0.001) were synthesized by high pressure and high temperature method (HPHT). Thermoelectric properties of PbTe1−xIx are investigated in the range of 300–600 K. The carrier concentration of PbTe prepared by HPHT is more sensitive to I content compared to that of the PbTe1−xIx sample prepared by other methods. The resistivities and the absolute values of Seebeck coefficients for PbTe1−xIx increase while the thermal conductivities decrease with increasing temperature. A large power factor of 39.1 μW/(cmK2) at room temperature is obtained with the carrier concentration of 9.7 × 1018 cm−3, which is much higher than that of Sb and Bi doped PbTe with the same synthesizing conditions. The high power factor is attributed to the high Hall mobility and large effective mass. The maximum figure-of-merit, ∼0.71 @ 600 K, is obtained for the samples with the carrier concentration of 9.7 × 1018 cm−3.

Rapid synthesis and thermoelectric properties of clathrate Ba8Cu6Ge15Si25 by high temperature and high pressure

Ba8Cu6Ge[Formula: see text]Si[Formula: see text] were successfully synthesized by a simple high pressure and high temperature (HPHT) method to investigate the microstructures and thermoelectric (TE) properties. After high pressure synthesis, a highly dense bulk material with lots of fine-layered structure, lattice defects and disorders has been obtained. As expected, the thermal conductivity decreased greatly and the ZT value has been improved significantly, which reaches up to 0.43 at around 773 K. Comparing with other methods, HPHT could shorten the synthesis time from several days to half an hour. It reveals that the HPHT method will become an effective approach for optimizing the TE performance of these materials.

Thermoelectric properties of In-filled and Te-doped CoSb3 prepared by high-pressure and high-temperature

A novel chemical alloying method of high-pressure and high-temperature (HPHT) has been used for the synthesis of bulk-skutterudite [Formula: see text]. Through HPHT method, the synthesis time has been shortened from a few days to 30[Formula: see text]min. The samples of [Formula: see text] skutterudites were synthesized at 1.8–3.3[Formula: see text]GPa. We have studied the phase, the microstructure, and the temperature-dependent thermoelectric properties. The Seebeck coefficient, electrical conductivity and thermal conductivity were measured in the temperature range of 295–673[Formula: see text]K. As we expected, the thermal conductivity of sample [Formula: see text] decreased with the increase of the synthetic pressure. A maximal ZT of 0.64 was achieved for the [Formula: see text] synthesized at 1.8[Formula: see text]GPa at 673[Formula: see text]K. These results revealed that HPHT method may be helpful for optimizing electrical conductivity and thermal conductivity in a comparatively independent way.

Preparation of ZrO2 whiskers through high pressure and high temperature method

ZrO2 whiskers have been successfully synthesized at temperature of 1800 °C and high pressure of 15 GPa, using ZrO2 powder as the starting material. After a high pressure and high temperature (HPHT) process, a bunch of long and idiomorphic ZrO2 whiskers are obtained. The grown whiskers look like needles, and have silky luster. They are colorless and transparent, and exhibit hexagonal, triangular, quadrilateral, and irregular shaped cross sections. Through this HPHT method, whiskers with various diameters from 10 to 20 μm, and length from 200 to 1000 μm can be produced. The aspect ratio of length to diameter can be from 10 to 100. Growth mechanism of the ZrO2 whiskers prepared under HPHT conditions are discussed, and the ZrO2 whiskers growth may undergo a vapor–solid process.

The Enhanced Thermoelectric Properties of Ba0.4Co4Sb11.7Te0.3 Prepared by the High-Pressure and High-Temperature Method

AbstractPolycrystalline skutterudite Ba0.4Co4Sb11.7Te0.3 with a bcc crystal structure was prepared by the High-Pressure and High-Temperature (HPHT) method. The study explored a chemical method for introducing Ba atoms into the voids of CoSb3 to optimize the thermoelectric figure of merit ZT in the system of Ba0.4Co4Sb11.7Te0.3. The samples were characterized by X-ray diffraction, electron microprobe analysis, and thermoelectric properties measurement. The electrical resistivity, Seebeck coefficients and thermal conductivities of the samples were measured in the temperature range of 300–743 K. The power factor and the figure of merit, ZT, of the samples all increased with the increasing temperature. A dimensionless thermoelectric figure of merit of 0.87 at 743 K was achieved for n-type Ba0.4Co4Sb11.7Te0.3 at last. The results indicated Ba-filled CoSb3 prepared by HPHT method is an effective method to greatly enhance the thermoelectric properties of skutterudite compounds.

Electrochemical Activity of Black Phosphorus as an Anode Material for Lithium-Ion Batteries

Black phosphorus (black P), which is a promising candidate as an anode material for lithium-ion batteries, was synthesized by a high-pressure and high-temperature (HPHT) method from white and red phosphorus. The study revealed the electrochemical activity of pure black P under different pressures and temperatures systematically. The sample shows higher crystallinity and purity by the HPHT method. Lithium-ion batteries containing black phosphorus as anode materials exhibited a high specific capacity and excellent cycling performance. Black phosphorus obtained from white phosphorus exhibited the highest first discharge and charge capacities of 2505 and 1354 mAh·g–1 at 4 GPa and 400 °C and that obtained from red phosphorus exhibited the highest first discharge and charge capacities of 2649 and 1425 mAh·g–1 at 4.5 GPa and 800 °C. Black P was characterized by X-ray diffraction, Raman microscopy, scanning electron microscopy, and high-resolution transmission electron microscopy.

Characterization of impurities in cubic boron nitride crystallites with thermoluminescence and ionoluminescence

IonoLuminescence (IL) and ThermoLuminescence (TL) techniques have been used in order to characterize the defects induced by doping due to different precursors in cubic boron nitride (c-BN) growth. Crystallites of dimensions of the order of 10–40 μm obtained by HPHT (High Pressure and High Temperature) method were used. Protons microbeams of 2 MeV – corresponding to a penetration depth of 26 μm in c-BN – with a spot diameter of few μm, in connection with an ellipsoidal mirror characterized by a large light collection efficiency and a 0.25 m monochromator, allowed to acquire wide area luminescence spectra. We observed that IL spectra for samples characterized by a large Mg content, as obtained by PIXE (Particle Induced X-ray Emission) analysis, displayed three peaks at 1.95 eV, 3.2 eV and 3.9 eV respectively, while in samples with a large Ca content a fourth peak appeared around 1.7 eV. Even if the number of available samples was relatively low, a fair correlation was observed between the total area under the peaks at 1.7 and 1.95 eV and the total Ca content (up to 25 ppm) on one side and between the total area under the peak at 3.9 eV and the total Mg content (up to 100 ppm), even if this peak appeared with a much smaller intensity also in all the other samples. Moreover, TL measurements were carried out from RT up to 400 °C with a standard Harshaw TL reader after the exposure of samples to some Gy doses from a collimated α-particle 241Am source. Specimens obtained by a Mg-based precursor did not show any thermoluminescence, while samples obtained by a Ca-based precursor showed a large and very reproducible TL spectrum. From the initial rise TL method, coupled to a preheating in order to separate the contributions from different traps, three series of centres were found out at 0.21, 0.35 and 0.6 eV. Samples obtained without a Ca-based precursor probably have a level at 0.45 eV instead of at 0.35 eV and, likely, there is also another level at 0.52 eV in Ca-doped platelets. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)