High Pressure And High Temperature Synthesis Research Articles

Tin disulfide with bright near-IR luminescence centers obtained at high pressures

In this work, the high-pressure and high-temperature (HPHT) method was applied to obtain crystalline tin disulfide (${\mathrm{SnS}}_{2}$). The synthesis was performed in a sulfur-tin-carbon growth system by placing the reaction mixture of sulfur and tin in a graphite capsule. The synthesized ${\mathrm{SnS}}_{2}$ demonstrated to be a highly crystalline $2H$-polytypic form suitable for mechanical exfoliation of atomically thin films. The crystals reveal strong near-IR photoluminescence attributed to a new luminescence center in ${\mathrm{SnS}}_{2}$. At 5 K, this center is characterized by a narrow zero-phonon line at 885 nm and phonon sideband whose structure is governed by ${\mathrm{SnS}}_{2}$ phonon density of states. Based on $\mathit{ab}$ initio calculations, the center is attributed to carbon in the tin sublattice. The side product of the HPHT synthesis is the diamond phase containing optically active tin-vacancy centers (${\mathrm{SnV}}^{\ensuremath{-}}$).

HPHT synthesis and enhanced thermoelectric transport properties of double-doped Co4Sb11TexSn1-x skutterudites

The high-pressure and high-temperature (HPHT) technique was employed to prepare skutterudite-based polycrystalline materials Co4Sb11TexSn1-x (x = 0.5, 0.6, 0.7). The thermoelectric properties, as well as electrical transport properties near room temperature, were researched systematically. The results indicated that the Sn and Te co-doped specimens yielded an impressive depression in lattice thermal conductivity (κL) based on the point-defect scattering. The κL exhibited a positive Te doping level dependence. Therefore, a minimum lattice thermal conductivity was 1.41 Wm−1K−1 for Co4Sb11Te0.7Sn0.3. Consequently, the thermoelectric dimensionless figure of merit, ZT, was remarkably enhanced from 300 to 725 K. The maximum ZT was 1.13 for Co4Sb11Te0.7Sn0.3 at 711 K, which is better than that of pure Co4Sb12. This value is nearly improved one order of magnitude and rivals the state-of-the-art single-filled n-type skutterudite compounds. Compared to the traditional synthesized method, high pressure and high-temperature techniques can fundamentally reduce the reaction duration from several days to less than an hour and provide a different route for the synthesis of thermoelectric materials.

HPHT Synthesis: Effects of the Synergy of Pressure Regulation and Atom Filling on the Microstructure and Thermoelectric Properties of Yb x Ba8-x Ga16Ge30.

Type-I clathrate compounds YbxBa8–xGa16Ge30 have been synthesized by the high-pressure and high-temperature (HPHT) method rapidly. The effects of the synergy of atom filling and pressure regulation on the microstructure and thermal and electrical properties have been investigated. With the content of Yb atom increasing, the carrier concentration is improved, the electrical resistivity and the absolute Seebeck coefficient are decreased, while the thermal conductivity is reduced significantly. A series of extremely low lattice thermal conductivities are achieved, attributed to the enhancement of multiscale phonon scattering for the “rattling” of the filled guest atoms, the heterogeneous distribution of nano- and microstructures, grain boundaries, abundant lattice distortions, lattice deformations, and dislocations. As a result, a maximum ZT of about 1.07 at 873 K has achieved for the Yb0.5Ba7.5Ga16Ge30 sample.

Mechanical properties of tantalum carbide from high-pressure/high-temperature synthesis and first-principles calculations.

As a member of the refractory metal carbide family of materials, TaC is a promising candidate for ultra-high temperature ceramics (UHTC) with desirable mechanical strength. TaC sample quality and therefore mechanical properties are strongly dependent on synthesis method, and atomistic origins of mechanical failure are difficult to assign. Here, we have successfully synthesized high quality densified TaC samples at 5.5 GPa and 1400 °C using the high pressure and high temperature (HPHT) sintering method, with Vickers hardness determined to be 20.9 GPa. First-principles calculations based on the recently developed strain-stress method show that the ideal indentation strength of TaC is about 23.3 GPa in the (11[combining macron]0)[001] direction, in excellent agreement with experimental results. The detailed indentation shear deformation analysis and structural snapshots from the calculations indicate that the slip dislocations of TaC layers are the main structural deformation mode during the Vickers indentation process, and that the strong directional Ta-C bonds are responsible for the high mechanical strength of TaC. HPHT synthesis is shown to produce TaC samples with superior strength, and together with accurate first-principles calculations offers crucial insights for rational design and synthesis of novel and advanced UHTC materials.

HPHT synthesis and enhanced TE performance of Te and Sn/Se elements binary-doped CoSb3

A series of binary-doped CoSb3 with Te and Se/Sn bulk compounds Co4Sb[Formula: see text]TexSny/Sey ([Formula: see text] and 0.6, [Formula: see text] and 0.3), have been successfully prepared via a simple high pressure and high-temperature (HPHT) method. And, the influence of the doping elements on the microstructure of the samples synthesized under diverse pressures and the corresponding TE performance were studied in detail. Comparing with other preparation methods, the synthesis time of HPHT was acutely shortened. The obtained samples contain more grain boundaries, lattice disorder, dislocations and the possible “nanodot”, which have positive effect on reducing thermal conductivity. The experimental data indicate that the absolute values of Seebeck coefficient increases with pressure. What’s more, the thermal conductivities show a monotone decreasing trend as the synthesis pressure rises. The minimum value obtained is 1.93[Formula: see text]Wm[Formula: see text]K[Formula: see text] at normal temperature for Co4Sb[Formula: see text]Te[Formula: see text]Se[Formula: see text] prepared under 3[Formula: see text]GPa.

Studies on HPHT synthesis and N defects of N-rich B-doped diamonds

In this paper, high-quality N-rich single crystal diamonds with different boron additive contents were synthesized in NiMnCo alloy with high Ni content by the temperature gradient growth method under HPHT (high pressure and high temperature) conditions.

N-type Ba0.3Ni0.15Co3.85Sb12 skutterudite: High pressure processing technique and thermoelectric properties

In this letter, Ni substitution for Co and Ba filling into the voids were simultaneously applied to the CoSb3 bulks by the high pressure and high temperature (HPHT) method. As the results, the polycrystalline Ba0.3Ni0.15Co3.85Sb12 skutterudite bulks were successfully synthesized and the systematic thermoelectric properties were investigated. In our experiments, the synthesized time was sharply shortened to 30 min, which is markedly an advantage for mass production. The multiple textures and microstructures were revealed, including vortices-like structures, defects, and lattice dislocations. Remarkably, pressure tuning led to the increase of the Seebeck coefficient and electrical resistivity, yielding an optimized power factor of 11.7 × 10−4 Wm−1K−2 in the Ba0.3Ni0.15Co3.85Sb12 sample prepared at 3 GPa at room temperature, which yielded a 10-fold improvement in power factor and showed distinct reduction of thermal conductivity compared with pure CoSb3 sample. The maximum zT value 0.91 was obtained at 700 K for Ba0.3Ni0.15Co3.85Sb12 sample. The experimental results suggest that the effective elements doping combining with HPHT synthesis could optimize electrical and thermal transport properties in skutterudites.

One-step synthesis of type-I silicon clathrate Ba8Si46 under high pressure and high temperature

In this paper, the silicon clathrate [Formula: see text] was successfully synthesized using low-cost antioxidative azide [Formula: see text] and Si as precursors by means of high pressure and high temperature (HPHT). The clathrate phase was one-step synthesized by high pressure chemical method within a short time. The reaction temperature and pressure were optimized to achieve good-quality crystalline products with a composition of [Formula: see text] and its transition temperature [Formula: see text] is about 8.3 K. The new preparation route presented in this paper provides an alternative to the multistep HPHT synthesis applied so far. One-step synthesis of type-I silicon clathrate [Formula: see text] by high pressure chemical method can shorten the synthesis period of time greatly.

HPHT synthesis of N–H co-doped diamond single crystals

In this paper, a series of nitrogen and hydrogen elements (N–H) co-doped diamond single crystals were synthesized in the NiMnCo–C system with melamine (C3N6H6) additive by temperature gradient growth (TGG) method under high-pressure and high-temperature (HPHT). High nitrogen and hydrogen growth environment obviously reduces the growth rate of the diamond. The synthetic diamond crystals are octahedral shape with a green or dark green color. This results indicate that the morphology of the synthetic N–H co-doped gem-diamond can be well-controlled by TGG method. Fourier transform infrared spectroscopy (FTIR) indicate that high-quality diamond single crystals with nitrogen concentrations up to 2100ppm have been successfully synthesized and the hydrogen related peaks at 2850cm−1 (sp3–CH3) and 2920cm−1 (sp3–CH2–) are found in these synthetic diamond. Meanwhile, with the increasing of C-centers the nitrogen atoms aggregate and form into A-centers in these synthetic diamonds. This is the highest quality of N–H co-doped gem-diamond single crystal synthesized in high nitrogen and high hydrogen growth environment reported so far.

HPHT synthesis and crystalline quality of large high-quality (001) and (111) diamond crystals

High-quality type IIa diamond crystals measuring up to 12mm in diameter (8 to 10 carats) were successfully grown by the temperature gradient method at high pressure and high temperature (HPHT) on defect-free (001)-oriented and (111)-oriented seed crystals. The crystalline quality of the grown crystals was qualitatively evaluated by synchrotron based X-ray topograph and rocking curve (RC) measurements. The results revealed that the crystals grown on (001)-oriented seeds have extremely high quality in the (001) growth sector, which extends straight upward from the seed surface. This sector contains very few dislocations and stacking faults in the upper part in particular, where the RC almost agrees with the theoretical curve. For the crystals grown on (111)-oriented seeds, it was confirmed that crystal defects are fewer in the outer (100), (010), and (001) growth sectors than in the central (111) growth sector extending straight upward from the seed surface. The RCs in selected regions of these {100} growth sectors are close to the theoretical curve, indicating high crystalline quality.

HPHT synthesis and magnetic property of -Fe2O3@C core-shell nanorods

-Fe2O3@C core-shell nanorods with average diameter of 20 nm and length of 150 nm are synthesized by transforming FeOOH@PVA nanorods under the condition of high pressure and high temperature (HPHT). The FeOOH@PVA nanorods are prepared via a hydrothermal route. The best synthesis condition for transforming FeOOH@PVA core-shell nanorods into -Fe2O3@C nanorods is 400 ℃ under 1 GPa. Owing to high aspect ratios, the -Fe2O3@C nanorods present a high coercivity of 330 Oe (10 Oe=79.5775 A/m). The possible mechanism for the synthesis of -Fe2O3@C nanorods is also discussed. The HTHP method can provide a new way for preparing of one-dimensional core-shell nanostructures.

Effects of additive NaN3 on the HPHT synthesis of large single crystal diamond grown by TGM

In this paper, large single crystal diamond with perfect shape and high nitrogen concentration approximately 1671–1742 ppm was successfully synthesized by temperature gradient method (TGM) under high pressure and high temperature (HPHT). The HPHT synthesis conditions were about 5.5 GPa and 1500–1550 K. Sodium azide (NaN3) with different amount was added as the source of nitrogen into the synthesis system of high pure graphite and kovar alloy. The effects of additive NaN3 on crystal growth habit were investigated in detail. The crystal morphology, nitrogen concentration and existing form in synthetic diamond were characterized by means of scanning electron microscope (SEM) and infrared (IR) absorption spectra, respectively. The results show that with an increase of the content of NaN3 added in the synthesis system, the region of synthesis temperature for high-quality diamond becomes narrow, and crystal growth rate is restricted, whereas the nitrogen concentration in synthetic diamond increases. Nitrogen exists in diamond mainly in dispersed form (C-centers) and partially aggregated form (A-centers). The defects occur more frequently on crystal surface when excessive NaN3 is added in the synthesis system.

HPHT synthesis and electrical transport properties of Sm xCo 4Sb 12

Samarium-filled skutterudites Sm x Co 4Sb 12 ( x=0.5, 1.0) skutterudite thermoelectric (TE) materials with enhanced power factor were prepared by high-pressure and high-temperature (HPHT) technique. The microstructure properties were characterized with X-ray diffraction and scanning electron microscopy. The electrical resistivities and Seebeck coefficients of those samples were measured in the temperature range of 300–723 K, and the samples of Sm x Co 4Sb 12 showed n-type conduction. The Seebeck coefficient in absolute value of Sm x Co 4Sb 12 increased with an increase of temperature and decreased with an increase of x. Among all the samples, Sm 0.5Co 4Sb 12 showed the highest power factor of 2.5×10 −3 W/m/K 2 at 665 K. The results indicated that HPHT combined with samarium filling is an effective way to enhance the thermoelectric properties for skutterudite compounds.

HPHT Synthesis of High-Quality Diamond Single Crystals with Micron Grain Size

High-quality diamond single crystals with micron grain size are synthesized with a new high-pressure and high-temperature (HPHT) synthesis technique in a cubic anvil high pressure apparatus. Morphology of the synthesized diamonds is observed by a scanning electron microscope (SEM). The samples are characterized using laser Raman spectra. The results show that the new synthesis technique improves the nucleation of diamond greatly, and diamond single crystals with perfect morphology and micron grain size are successfully synthesized, with the average grain size of about 6μm. This work provides a new synthesis technique to implement industrialization of high-quality diamond single crystals with super-fine grain size, and paves the way for future development.

HPHT Synthesis of Micron Grade Boron-Doped Diamond Single Crystal in Fe-Ni-C-B Systems

Micron grade boron-doped diamond crystals with octahedral morphology are successfully synthesized in a Fe—Ni—C—B system under high pressure and high temperature (HPHT). The effects of the additive boron on synthesis conditions, nucleation and growth, crystal morphology of diamond are studied. The synthesized micron grade diamond crystals were characterized by optical microscope (OM), scanning electron microscope (SEM), x-ray diffraction (XRD) and Raman spectroscopy. The research results show that the V-shaped section of synthetic diamond moves downwards to the utmost extent due to 0.3a wt% (a is a constant.) boron added in the synthesis system. The crystal colour is black, and the average crystal size is about 25 μm. The crystal faces of synthetic diamond are mainly {111} face. The synthesis of this kind of diamond is few reported, and it will have important and widely applications.

HPHT synthesis and electrical properties of AgSbTe 2–Ag 2Te thermoelectric alloys

In this letter, p-type pseudo-binary AgSbTe 2–Ag 2Te thermoelectric alloys with the composition of (AgSbTe 2) 1 − x (Ag 2Te) x ( x = 0~0.2) were prepared by high pressure and high temperature (HPHT) method. The samples are near single phase AgSbTe 2 with a small quantity of impurities including Sb 2Te 3 and Ag 2Te. The electrical properties including the Seebeck coefficient and the electrical resistivity depending on synthetic pressure and the Ag 2Te content x were studied at room temperature. The measurement results show that the Seebeck coefficient and the electrical resistivity for (AgSbTe 2) 1 − x (Ag 2Te) x decrease with an increase of the synthetic pressure and x which indicate that high pressure combining alloying with Ag 2Te could modulate the electrical properties of Ag–Sb–Te system effectively.

HPHT synthesis of large single crystal diamond doped with high nitrogen concentration

Large green single crystal diamond with high nitrogen concentration is firstly synthesized by temperature gradient method under high pressure and high temperature (HPHT). Sodium azide (NaN 3) is added as the source of nitrogen to the synthesis system of high pure graphite and kovar alloy (Fe 59Co 25Ni 17). The HPHT synthesis condition is 5.4 GPa and 1480 K. The maximum crystal size is 3.2 mm. The infrared absorption spectra indicate that the nitrogen concentration in the green large single crystal diamond reaches 1520 ppm in the form of single substitution, which is close to that in nature diamond, and several times higher than that in the man-made Ib large single crystal diamond previously.