High-pressure High-temperature Method Research Articles

Effect of thermobaric treatment on magnetic and superconductive properties of HPHT-grown nitrogen-doped diamond crystals

The effect of thermobaric treatment (TBT) at Р = 5.5 GPa T = 1900 °C for 4 h on the concentration of single substitutional atoms (P1 centers) in nitrogen-doped synthetic single crystal Ib type diamonds grown by the temperature gradient high-pressure high-temperature (TG-HPHT) method and on their magnetic properties in the temperature range of 2–300 K was investigated. The initial concentration of P1 centers in 2 crystals was 3.0 × 1019 cm−3 and 5.6 × 1019 cm−3, respectively, which decreased by ~96–98 % after TBT. At T < 10 K, an anomalous hysteresis of the magnetic moment is observed in the range of magnetic fields up to Hc = 70 kOe, the amplitude of which is half the value of the paramagnetic saturation moment, corresponding to the number of spins of the P1 centers. The shape of the hysteresis loops after subtracting an intrinsic diamond diamagnetic component and the calculated paramagnetic component indicates a granular (local) superconducting state. The fact that the amplitude of the magnetic moment generated by superconducting currents is equal to half the total number of Bohr magnetons of P1 centers may indicate that elementary currents occur in pairs of adjacent P1 centers. As a result of a decrease in the number of P1 centers in diamonds after TBT, the saturation values of the paramagnetic moment and the amplitude of the diamagnetic moment of the induced superconducting currents decrease proportionally.

Atomically Unraveling Highly Crystalline Self-Intercalated Tantalum Sulfide with Correlated Stacking Registry-Dependent Magnetism.

In self-intercalated two-dimensional (ic-2D) materials, understanding the local chemical environment and the topology of the filling site remains elusive, and the subsequent correlation with the macroscopically manifested physical properties has rarely been investigated. Herein, highly crystalline gram-scale ic-2D Ta1.33S2 crystals were successfully grown by the high-pressure high-temperature method. Employing combined atomic-resolution scanning transmission electron microscopy annular dark field imaging and density functional theory calculations, we systematically unveiled the atomic structures of an atlas of stacking registries in a well-defined √3(a) × √3(a) Ta1.33S2 superlattice. Ferromagnetic order was observed in the AC' stacking registry, and it evolves into an antiferromagnetic state in AA/AB/AB' stacking registries; the AA' stacking registry shows ferrimagnetic ordering. Therefore, we present a novel approach for fabricating large-scale highly crystalline ic-2D crystals and shed light on a powerful means of modulating the magnetic order of ic-2D systems via stacking engineering, i.e., stackingtronics.

Ordinary-pressure phase transition from graphite to diamond induced by monodispersed Ta atoms

High pressure high temperature (HPHT) was conventionally required for the phase transition from graphite to diamond. Here, we deposited monodispersed Ta atoms on pressed pure graphite substrate in hot filament chemical vapor deposition system and then performed annealing on the sample under ordinary pressure, letting graphite transit to diamond. Specifically, along the longitudinal direction the unannealed sample is divided into three regions of TaC particles, amorphous carbon and graphite, and 2–3 nm sized diamond grains are only observed among the TaC particles. After annealing the sample under 1000 °C for 15 min, diamond grains not only form among TaC particles, but also appear in amorphous carbon region. It is observed that more diamond grains with larger size of 3–10 nm and diamond variant structures i-Carbon (i-C) with the size larger than 30 nm are formed in amorphous carbon region. And more monodispersed Ta atoms are distributed in the amorphous carbon region of the annealed sample. This suggests that monodispersed Ta atoms firstly change graphite into amorphous carbon and then induce its transformation into i-C and diamond. Our results give a different way from HPHT method to prepare diamond based on graphite under ordinary pressure.

Investigating the elastic, mechanical, and thermal properties of polycrystalline Mo2C under high pressure and high temperature

Understanding pressure-induced acoustic velocity-elasticity behavior has extraordinary significance in the fields of materials science and earth science. Herein, we used an advanced high-pressure high-temperature (HPHT) method to synthesize pure-phase β-Mo2C bulk ceramics. The sound velocity-elasticity behavior, thermodynamic properties, and mechanical behavior of the synthesized β-Mo2C ceramics were systematically investigated by in-situ high-pressure ultrasonic interferometry and theoretical calculations. The compressive and shear wave velocities, isothermal bulk modulus, shear modulus, Vickers hardness, fracture toughness, Debye temperature, and melting temperature of polycrystalline β-Mo2C exhibited a monotonic increase with increasing pressure. The experimental and calculation results showed that β-Mo2C had strong ductile behavior and was a ductile ceramic. Additionally, the temperature-hardness relationship of the as-synthesized polycrystalline β-Mo2C was investigated by in-situ high-temperature Vickers indentation measurements. The hardness of β-Mo2C gradually decreased with increasing temperature, and this ceramic still maintained a hardness as high as 12.3 GPa at 500 °C. These results suggest that the intrinsic mechanical and thermodynamic properties of β-Mo2C are dominated by its unique electronic structure and bonding mode.

Study on Structural Evolution of Synthetic Graphite Derived from Lignite Prepared by High Temperature–High Pressure Method

Abundant and cheap lignite is regarded as inferior fuel due to its disadvantages such as low heat and high moisture. In order to realize the high value and clean, non-fuel utilization of lignite, we used lignite as precursor to prepare high-quality synthetic graphite through graphitization treatment using the high temperature–high pressure (HTHP) method, and afterwards characterized the samples by XRD, Raman, FTIR, SEM-EDS, and HRTEM, and systematically analyzed the effect of P-T conditions on the structure evolution of lignite. Our results demonstrated that temperature dominates the graphitization of lignite, and high pressure accelerates the graphitization process of lignite. Under HTHP treatment, the aromatic layer of lignite accelerates directional rearrangement; the ordered domain increases rapidly, and the ductility and stacking degree of the carbon sheets of the lignite sample are greatly enhanced. Compared with the traditional high-temperature graphitization method, the HTHP method greatly reduces the graphitization temperature and shortens the graphitization time. Remarkably, the as-prepared graphite with a graphitization degree of 91.87% superior to graphite fabricated by the conventional high-temperature processing were rapidly prepared from lignite at 6 GPa and 1300 °C in 20 min. This study demonstrates that the HTHP method is a feasible and effective method to realize the green, efficient, and high value utilization of lignite.

Structural and Optical Properties of Silicon Carbide Powders Synthesized from Organosilane Using High-Temperature High-Pressure Method.

The development of new strategies for the mass synthesis of SiC nanocrystals with high structure perfection and narrow particle size distribution remains in demand for high-tech applications. In this work, the size-controllable synthesis of the SiC 3C polytype, free of sp2 carbon, with high structure quality nanocrystals, was realized for the first time by the pyrolysis of organosilane C12H36Si6 at 8 GPa and temperatures up to 2000 °C. It is shown that the average particle size can be monotonically changed from ~2 nm to ~500 nm by increasing the synthesis temperature from 800 °C to 1400 °C. At higher temperatures, further enlargement of the crystals is impeded, which is consistent with the recrystallization mechanism driven by a decrease in the surface energy of the particles. The optical properties investigated by IR transmission spectroscopy, Raman scattering, and low-temperature photoluminescence provided information about the concentration and distribution of carriers in nanoparticles, as well as the dominant type of internal point defects. It is shown that changing the growth modes in combination with heat treatment enables control over not only the average crystal size, but also the LO phonon—plasmon coupled modes in the crystals, which is of interest for applications related to IR photonics.

Confined Chemical Transitions for Direct Extraction of Conductive Cellulose Nanofibers with Graphitized Carbon Shell at Low Temperature and Pressure.

Cellulose is the most abundant renewable natural polymer on earth, but it does not conduct electricity, which limits its application expansion. The existing methods of making cellulose conductive are combined with another conductive material or high-temperature/high-pressure carbonization of the cellulose itself, while in the traditional method of sulfuric acid hydrolysis to extract nanocellulose, it is usually believed that a too high temperature will destroy cellulose and lead to experimental failure. Now, based on a new research perspective, by controlling the continuous reaction process and isolating oxygen, we directly extracted intrinsically conductive cellulose nanofiber (CNF) from biomass, where the confined range molecular chains of CNF were converted to highly graphitized carbon at only 90 °C and atmospheric pressure, while large-scale twisted graphene films can be synthesized bottom-up from CNFene suspensions, called CNFene (cellulose nanofiber-graphene). The conductivity of the best CNFene can be as high as 1.099 S/cm, and the generality of this synthetic route has been verified from multiple biomass cellulose sources. By comparing the conventional high-pressure hydrothermal and high-temperature pyrolysis methods, this study avoided the dangerous high-pressure environment and saved 86.16% in energy. These findings break through the conventional notion that nanocellulose cannot conduct electricity by itself and are expected to extend the application potential of pure nanocellulose to energy storage, catalysis, and sensing.

A novel and efficient catalyst system composed of detonation nanodiamond and potassium iodide for chemical fixation of carbon dioxide

In this paper, we report a novel, unusual catalytic system that can efficiently catalyze the cycloaddition of CO2 with propylene oxide to form propylene carbonate in a mild solvent-free condition based on the combination of detonation nanodiamond (DND) and potassium iodide (KI). When the reaction was carried out at 0.8 MPa pressure and 90 °C for 6 h, the reaction catalyzed by DND-KI (e.g. 1.0 mol% KI relative to propylene oxide(PO), DND: KI = 0.8:1 wt/wt) has a yield as high as 96.4%, which is much higher than that catalyzed by DND with other substances such as potassium bromide, potassium chloride, tetrabutylammonium iodide, and 1-butyl-3-methylimidazolium iodide. DND-KI also shows a higher catalytic reaction yield than the catalyst systems from other carbon nanomaterials such as graphene, carbon nanotube and nanodiamond prepared by a high-pressure high-temperature method. The DND-KI has an excellent service life. After ten cycles of reaction, it has almost no loss in catalytic activity. DND-KI is also applicable to the cycloaddition of CO2 with other epoxides. We further show that the excellent catalysis capability of DND-KI originates from the special subsidiary functional groups (e.g. hydroxyl and carboxyl groups) that the DND possesses and a synergetic effect between those functional groups and KI during the reaction. The large specific surface area and porous structure also facilitate the reaction.

Development of a novel triple-layer polycrystalline diamond compact

The objective of this research was to obtain a triple layer Polycrystalline Diamond Compact (PDC) via the High-pressure High-temperature (HPHT) sintering method. A thin layer of WC with 20 wt% Nb/Ni was used as an interface between the top layer of Polycrystalline Diamond (PCD) with pure Nb binder and WC 10 wt% Co substrate. Sintering was performed at 1750 °C under 7.7 GPa of pressure. Microhardness variation was measured and microstructural/structural studies were done via SEM/EDS and XRD. The overall results showed that this new kind of PDC can be produced successfully using pure niobium as a binder for the PDC layer and no sign of graphitization was detected. It was also found that using an interface having the resemblance to both substrate and sintered diamond body caused good adhesion between layers that can potentially enhance performance and durability of PDC.

Two-step high-pressure high-temperature synthesis of nanodiamonds from naphthalene**Project supported by the National Key R&D Program of China (Grant No. 2018YFB0406500), the National Natural Science Foundation of China (Grant Nos. U1804155, U1604263, and 11804307), and the China Postdoctoral Science Foundation (Grant Nos. 2018M630830 and 2019T120631).

Nanodiamonds have outstanding mechanical properties, chemical inertness, and biocompatibility, which give them potential in various applications. Current methods for preparing nanodiamonds often lead to products with impurities and uneven morphologies. We report a two-step high-pressure high-temperature (HPHT) method to synthesize nanodiamonds using naphthalene as the precursor without metal catalysts. The grain size of the diamonds decreases with increasing carbonization time (at constant pressure and temperature of 11.5 GPa and 700 °C, respectively). This is discussed in terms of the different crystallinities of the carbon intermediates. The probability of secondary anvil cracking during the HPHT process is also reduced. These results indicate that the two-step method is efficient for synthesizing nanodiamonds, and that it is applicable to other organic precursors.

Low-Power Laser Graphitization of High Pressure—High Temperature Nanodiamond Films

Laser-induced graphitization of 100 nm monocrystals of diamond particles synthesized by high-pressure high-temperature (HP-HT) methods is not typically observed. The current study demonstrates the graphitization of 150 nm HP-HT nanodiamond particles in ca. 20-μm-thick thin films formed on a glass substrate when the intensity of a focused 633 nm He-Ne laser exceeds a threshold of ~ 33 kW/cm2. Graphitization is accompanied by green luminescence. The structure and morphology of the samples were investigated before and after laser excitation while using X-ray diffraction (XRD), Raman spectroscopy, atomic force (AFM), and scanning electron microscopy (SEM). These observations are explained by photoionization of [Ni-N]- and [N]-centers, leading to the excitation of electrons to the conduction band of the HP-HT nanodiamond films and an increase of the local temperature of the sample, causing the transformation of sp3 HP-HT nanodiamonds to sp2-carbon.

High-pressure synthesis, crystal structures, and magnetic and dielectric properties of GdFeO3-type perovskites (Dy0.5Mn0.5)(Mn1−xTix)O3 with x = 0.5 and 0.75

(Dy0.5Mn0.5)(Mn1−xTix)O3 perovskite solid solutions with x = 0.5 and 0.75 were prepared by a high-pressure high-temperature method at 6 GPa and about 1570–1670 K. They have a GdFeO3-type perovskite structure with Pnma space group and random distributions of Dy3+ and Mn2+ cations at the A site, and Mn3+/2+ and Ti4+ cations at the B site. Their crystal structures were investigated using synchrotron X-ray powder diffraction at room temperature. The x = 0.5 sample shows a ferrimagnetic transition below TC = 50 K and dielectric constant of about 25 between 10 and 150 K. The x = 0.75 sample shows a ferrimagnetic-like transition below TC = 20 K and temperature-independent dielectric constant of about 100 between 10 and 250 K.

Effect of N, N′-m-phenylene bismaleimide on mechanical performance of waste rubber powder sintered by high-pressure high-temperature method

Waste rubber with three-dimensional structure is insoluble and non-melting, which creates recycling problem. The technique called “high-pressure high-temperature sintering” (HPHTS) can convert vulcanized rubber powder into usable rubber products. However, reversion occurs when vulcanizates are exposed to a prolonged treatment at high temperature. This reversion results in the decrease of mechanical properties of sintered waste rubber powder (WRP) samples. To address this problem, a method of enhancing the mechanical properties of sintered WRP by incorporating different content of maleic anhydride (MA) and N, N′-m-phenylene bismaleimide (BMI) is discussed in this paper. The results show that BMI and MA can slow down the formation of the conjugated double bonds. Through Diels–Alder reaction, BMI inhibits conjugated double bonds formation and improves the adhesion between particles and particles, which is beneficial to improvement of final properties. Therefore, BMI improves the mechanical properties of sintered WRP greatly.

Influence of High Pressure-High Temperature Method on the Selected Mechanical Properties of Steel AISI 316L with 2% TiB2

Influence of High Pressure-High Temperature Method on the Selected Mechanical Properties of Steel AISI 316L with 2% TiB2

Zirconium Phase Transformation under Static High Pressure and ω-Zr Phase Stability at High Temperatures.

High-purity Zr has been observed to undergo a phase transformation from the α-phase to the hexagonal ω-phase under high pressure generated either statically or by shock loading. The transition pressure from α-Zr to ω-Zr at 300 K is 2.10 GPa. The main aim of this research was to determine the conditions of α-Zr in ω-Zr transformation and the state of stresses after the high-pressure pressing and sintering of zirconium powders. Commercially acquired zirconium powders of 99.9% and 98.8% purity were used in this study. Qualitative and quantitative phase analysis of the materials was carried out using X-ray diffraction. The materials were statically pressed and sintered using a Bridgman-type toroidal apparatus at under 4.0 and 7.8 GPa. After pressing, the transformation proceeded for the zirconium powder containing 98.8% purity (with hydrides admixture) but did not occur for the high-purity zirconium powders with 99.9% purity. The zirconium powders were sintered using the HPHT (High Pressure—High Temperature) method at temperatures of 1273 K and 1473 K. The transformation proceeded for both powders. The highest contribution of the ω-Zr phase was obtained in the zirconium (98.8% purity with the hydrides contents) sintered for 1 min at a temperature of 1473 K and a pressure of 7.8. The ω-phase content was 87 wt.%. The stress measurement was performed for the pressed and sintered materials using the sin2ψ X-ray diffraction method. The higher sintering temperature resulted in a decrease of the residual stresses in the ω-Zr phase for the sintered zirconium. The higher levels of stress limited the transformation of the α-Zr phase into the ω-Zr phase. Investigated materials characterized by higher compressive macrostresses were also typical of the greater stability of the ω-Zr phase at high temperatures.

ZrC Based Ceramics by High Pressure High Temperature SPS Technique

Zirconium carbide based materials were consolidated via spark plasma sintering and high-pressure high-temperature (HPHT) sintering methods. Fully dense ZrC-TiC compacts were produced by HTHP SPS technique at 1600-1700°C and were characterized by 370 GPa and 23.7 GPa values of Young’s modulus and Vickers microhardness, respectively. By the addition of 2 wt.% silicon nitride, the compacts of a full density were obtained at 1600°C; however, the further addition of Si3N4 resulted in a decrease in both density and hardness. Oxidation behavior in air of the ZrC-TiC and ZrC-TiC-Si3N4 compacts was explored by high temperature XRD method showing intensive oxidation at ~1000°C. Microstructural analysis certified that the addition of certain amount of Si3N4 increases the phase distribution homogeneity and contributes to the microstructure refinement.

Sodium insertion in high pressure β-V2O5: A new high capacity cathode material for sodium ion batteries

β-V2O5, obtained by a high-temperature high-pressure method, exhibits a layered structure that favours the insertion of Na+. In this work, we report the electrochemical insertion of sodium in high pressure β-V2O5 and its performance as cathode material for sodium-ion batteries. The material shows a first discharge capacity of 132 mAh g−1 in the 3.6–2.0 V range at a C/20 current density and a maximum capacity of 147 mAh g−1 under equilibrium conditions, corresponding to the insertion of 1 Na+ ion per formula unit. The β-V2O5//Na cell delivers a specific energy as high as 370–410 Wh kg−1. The amount of inserted sodium points to the reduction of 50% of the available V5+ ions. After 20 cycles, the discharge capacity retains 86% of the initial capacity. Concerning the reaction mechanism of high pressure β-V2O5 upon sodium insertion/de-insertion, several phase transitions are inferred from the voltage-composition profile. Ex situ XRD reveals the appearance of several NaxV2O5 phases in the 0 ≤ x ≤ 1 compositional range, which are closely related with the non-sodiated high pressure β-V2O5 structure. An irreversible structural transformation occurs during the very first inserted sodium, at the beginning of the first discharge, and the original high pressure β-V2O5 structure is not recovered upon full Na+ extraction. Electrochemical performances are outstanding though.

Laser-driven proliferation of sp2-sp3 changes during anti-Stokes white light emission of μ-diamonds

The paper presents the investigations of laser-induced white light emission (LIWE) and structural changes in diamonds after continuous wavelength near infrared laser excitation. Micro-size diamonds were synthesized using high pressure high temperature method and then excited using continuous wavelengths near infrared (808, 975, 1064 nm) laser diodes in vacuum. The structure and morphology of the samples were investigated before and after laser excitation using XRD, Raman spectroscopy and SEM/FIB and TEM microscopy. Broadband, intense, anti-Stokes LIWE with very low threshold were observed. LIWE resulted in the graphitization of the diamond grain surface with different stages of graphitization depending on the excitation time. A model of an sp2-sp3 hybridization switch process assisting the multiphoton ionization and free to bound recombination of electron between two carbon atoms were proposed.

Enhanced thermoelectric power factor of half-Heusler solid solution Sc1-xTmxNiSb prepared by high-pressure high-temperature sintering method

Abstract In an effort to find new thermoelectric materials, a series of half-Heusler alloys Sc1-xTmxNiSb (x = 0.0, 0.25, 0.5, 0.75, 1.0) was synthesized by arc melting and subsequent high-pressure high-temperature sintering. The products were examined by means of X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectrometry. The crystal structure of each sample was established to be of the MgAgAs-type, and the cubic lattice parameter was found to behave in accordance to the Vegard's law. The electrical transport properties of the Sc1-xTmxNiSb alloys were determined via resistivity and thermoelectric power measurements performed at temperatures 2–950 K. For each sample a semiconducting-like behavior was found with rather small values of the room-temperature resistivity (ρ = 10–50 μΩm), and fairly large positive Seebeck coefficient (Smax = 80–136 μV/K). For the alloy Sc0.75Tm0.25NiSb, combination of relatively small ρ (similar to that of TmNiSb) with rather high S (comparable to that of ScNiSb) yielded the thermoelectric power factor PF = 1.2 × 10 mW/(m K2) at 650 K, which is about twice larger than that found for ScNiSb. Increasing the amount of Tm in Sc1-xTmxNiSb brings about significant reduction in the thermal conductivity at 350 K from about 6 W/(m K) to ca. 3 W/(m K), and consequently leads to sizable enhancement of the thermoelectric figure of merit.

Electrical Properties of High-Quality Synthetic Boron-Doped Diamond Single Crystals and Schottky Barrier Diodes on Their Basis

The temperature dependences of the specific resistance and Hall coefficient of high-quality synthetic boron-doped diamond single crystals grown via a high-pressure high-temperature method are studied. The concentration of acceptors in the (001) cut plates was varied in a range of 2 × 1015–3 × 1017 cm–3 by varying the concentration of boron in the growth mixture (0.0004–0.04 at %). Thin rectangular plates with the uniform concentration of boron and free from extended structural defects are cut out by a laser after the X-ray topography and mapping of UV luminescence. The concentrations of donors and acceptors in the samples are calculated from the data of the Hall effect and capacitance–voltage characteristics. The obtained results correlate with the concentration of boron in the growth mixture. The minimum compensation ratio of acceptors with donors (below 1%) is observed in the crystals grown with the concentration of boron in the growth mixture of 0.002 at %. The ratio increases when the amount of boron is increased or decreased. The samples grown at such a concentration of boron have the maximum mobility of charge carriers (2200 cm2/(V s) at T = 300 K and 7200 cm2/(V s) at T = 180 K). The phonon scattering of holes dominates throughout the range of temperatures (180–800 K), while the scattering by point defects (neutral and ionized atoms of the impurity) is insignificant. The diamond crystals which are grown from a mixture containing 0.0005–0.002 at % boron and have perfect quality and a lattice mechanism of scattering can be considered as a reference semiconductor.