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Noble gas (NG) is often used as a hydrostatic pressure-transmitting medium in high-pressure experiments. However, the NG atoms under compression are found to be readily trapped in the voids of some...

The precise determination of atomic position of materials is critical for understanding the relationship between structure and properties, especially for compounds with light elements of boron and single or multiple transition metals. In this work, the single crystal X-ray diffraction is employed to analyze the atomic positions of Co

The 660-km seismic discontinuity (D660) is the boundary between the Earth’s lower mantle and transition zone and is commonly interpreted as the dissociation of (Mg,Fe)2SiO4 ringwoodite to (Mg,Fe)SiO3 bridgmanite plus (Mg,Fe)O ferropericlase (post-spinel transition). Prominent features of D660 are significant depressions to 750 km and multiplicity beneath cold subduction zones. Previous high-pressure experiments provided negative but gentle Clapeyron slopes (−1.3 to −0.5 MPa/K) of the post-spinel transition. Thus, the post-spinel transition cannot interpret the D660 depression. Therefore, another phase transition with a steep negative slope is required, and the akimotoite−bridgmanite transition in (Mg,Fe)SiO3 is one candidate.In the current study, we determined the boundaries of the post-spinel (RBP) and akimotoite−bridgmanite (AB) phase transitions in the MgO-SiO2 system over a temperature range of 1250–2085 K using advanced multi-anvil techniques with in situ X-ray diffraction. We judged a stable phase assemblage by observing relative increase/decrease in the ratio of coexisting high- and low-pressure assemblages at spontaneously and gradually decreasing pressure and a constant temperature from diffraction intensities. Since this strategy is strictly based on the principle of phase equilibrium, it excludes problems in determining phase stability caused by sluggish kinetics and surface energy.We found that the RBP boundary has a slightly concave curve, whereas the AB boundary has a steep convex curve. The RBP boundary is located at pressures of 23.2–23.7 GPa in the temperature range of 1250–2040 K. Its slope varies from −0.1 MPa/K at temperatures less than 1700 K to −0.9 MPa/K at 2000 K with an averaged value of −0.5 MPa/K. The slope of the AB boundary gradually changes from −8.1 MPa/K at low temperatures up to 1300 K to −3.2 MPa/K above 1600 K. Based on these findings, we predict that, beneath cold subduction zones, ringwoodite should first dissociate into akimotoite plus periclase, and then akimotoite transforms to bridgmanite with increasing depth; these successive transitions cause the multiple D660. Moreover, the steep negative boundary of the AB transition should result in cold-slab stagnation due to significant upward buoyancy. Our predictions are supported by the seismological observations beneath cold (e.g., Tonga, Izu-Bonin) subduction zones.

Interlayer electronic coupling in two-dimensional materials enables tunable and emergent properties by stacking engineering. However, it also results in significant evolution of electronic structures and attenuation of excitonic effects in two-dimensional semiconductors as exemplified by quickly degrading excitonic photoluminescence and optical nonlinearities in transition metal dichalcogenides when monolayers are stacked into van der Waals structures. Here we report a van der Waals crystal, niobium oxide dichloride (NbOCl

Accepted manuscript of Xie, L., Chanyshev, A., Ishii, T., Bondar, D., Nishida, K., Chen, Z., Bhat, S., Farla, R., Higo, Y., Tange, Y., Su, X., Yan, B., Ma, S., Katsura, T., Simultaneous generation of ultrahigh pressure and temperature to 50 GPa and 3300 K in multi-anvil apparatus, Rev. Sci. Instr., 92, 103902, 2021. https://doi.org/10.1063/5.0059279

Nature 601, 69 - 73 (2022). doi:10.1038/s41586-021-04157-z, The 660-km seismic discontinuity is the boundary between the Earth���s lower mantle and transition zone and is commonly interpreted as the dissociation of ringwoodite to bridgmanite plus ferropericlase (post-spinel transition)1-3. A distinct feature of the 660-km discontinuity is its depression to 750 km beneath subduction zones4-10. However, in situ X-ray diffraction studies using multianvil techniques have demonstrated negative but gentle Clapeyron slopes of the post-spinel transition that do not allow a significant depression11-13. On the other hand, conventional high-pressure experiments face difficulties in accurate phase identification due to inevitable pressure changes during heating and the persistent presence of metastable phases1,3. Here, we determined the post-spinel and akimotoite-bridgmanite transition boundaries by multi-anvil experiments using in situ X-ray diffraction strictly based on the definition of phase equilibrium. The post-spinel boundary has almost no temperature dependence, whereas the akimotoite���bridgmanite transition has a very steep negative boundary at temperatures lower than ambient mantle geotherms. The large depressions of the 660-km discontinuity in cold subduction zones are thus interpreted as the akimotoite���bridgmanite transition. The steep negative boundary of the akimotoite-bridgmanite transition will cause slab stagnation due to significant upward buoyancy14,15., Published by Nature Publ. Group, London [u.a.]

Determination of the structures of materials involving more light elements such as boron-rich compounds is challenging and technically important in understanding their varied compositions and super...

Phase behaviors of nanocrystalline TiO2-II have not been well studied due to the difficulty in its preparations at ambient pressure. In this work, we prepared nanocrystallites of TiO2-II with avera...

Understanding the mineralogy of the Earth's interior is a prerequisite for unravelling the evolution and dynamics of our planet. Here, we conducted high pressure-temperature experiments mimicking the conditions of the deep lower mantle (DLM, 1800–2890 km in depth) and observed surprising mineralogical transformations in the presence of water. Ferropericlase, (Mg, Fe)O, which is the most abundant oxide mineral in Earth, reacts with H2O to form a previously unknown (Mg, Fe)O2Hx (x ≤ 1) phase. The (Mg, Fe)O2Hx has a pyrite structure and it coexists with the dominant silicate phases, bridgmanite and post-perovskite. Depending on Mg content and geotherm temperatures, the transformation may occur at 1800 km for (Mg0.6Fe0.4)O or beyond 2300 km for (Mg0.7Fe0.3)O. The (Mg, Fe)O2Hx is an oxygen excess phase that stores an excessive amount of oxygen beyond the charge balance of maximum cation valences (Mg2+, Fe3+ and H+). This important phase has a number of far-reaching implications including extreme redox inhomogeneity, deep-oxygen reservoirs in the DLM and an internal source for modulating oxygen in the atmosphere.

Mn2+:CsPbCl3 nanocrystals (NCs) were synthesized using a modified one-pot injection method, which exhibits significantly improved thermal stability. For the first time, the pressure-treated optical and structural properties of synthetic Mn2+:CsPbCl3 NCs were further investigated, and their associated intriguing electrical and photoelectric properties were revealed from impedance spectra and photocurrent measurements under compression. The pressure-dependent photoluminescence experienced an initial redshift before 1.7 GPa followed by a continuous blueshift, as evidenced by the bandgap shifts. High-pressure XRD spectra uncovered a cubic-to-orthorhombic structural transition at about 1.1 GPa and subsequent amorphization upon further compression, which was fully reversible. Furthermore, the sample annealing from 340 K drove grain growth and decreased grain boundary resistance at ambient pressure. The compression further decreased the grain boundary barrier and improved the electrical conductivity (up to ∼10−2 Ω−1 cm−1) of the thermally annealed Mn2+:CsPbCl3 NC surface. Simultaneous photocurrent enhancement of thermally annealed NCs was also achieved as expected, and reached optimal performance at 0.7 GPa. Strikingly, after the pressure cycling (loading–releasing), the results show that thermally annealed Mn2+:CsPbCl3 NCs gained preservable higher electrical conductivity (∼10 times increase) and an improved photoelectric response compared to the ambient state before compression. This work proves that high pressure is useful for opening the versatility in the structure and properties of metal–halide perovskite nanocrystals leading to a promising way for superior optoelectronic materials-by-design.

The structural phase transition of synthetic ZnFe2O4 nanoparticles (ZFO NPs) is investigated as a function of pressure up to 40.6 GPa at room temperature for the first time, and its associated intriguing electrical transport properties are resolved from in situ impedance spectra and magnetoresistivity measurements. Significant anomalies are observed in the properties of the grain boundary resistance (Rgb), the relaxation frequency (fmax), and the relative permittivity (er) in the ZFO NPs under the pressures around 17.5–21.5 GPa. These anomalies are believed to be correlated with a cubic-to-orthorhombic phase transition of ZnFe2O4 at the pressures between 21.9 and 25.7 GPa, which is found to be partially reversible. The pressure-tuned dielectric properties are measured for the cubic and the orthorhombic phases of ZFO, respectively. Remarkably, Rgb decreases up to 6 orders of magnitude as a function of pressure in the cubic phase. The dielectric polarization is obviously strengthened with increased fmax and...

In this study, type Ib diamond annealing experiments were successfully performed under a pressure of 2.5 GPa and a high temperature range between 1680 and 2060 °C. The color of the diamond changed ...

In this study, single crystal diamonds were successfully synthesized in a FeNi-S-C system under the constant conditions of 5.5 GPa and 1400 °C. The growth rate of the diamonds decreased due to the existence of sulfur (S) in the synthesis system. The color of the diamonds changed from yellow to light yellow with an increase in the S content. Compared to common type Ib diamonds synthesized in a FeNi-C system, the nitrogen concentration was higher in the synthesized diamonds when 0.1 wt% S was added but was lower when the amount of S was increased to 0.25 wt%. Raman measurements indicated that the use of S had almost no effect on the diamond lattice structure, thus diamond crystals with a high-quality sp3 structure were obtained. The photoluminescence (PL) spectra showed that the nitrogen-vacancy (NV) center occurred more likely in diamond lattice growth along the {111} face. Compared to the NV− center, the NV0 center could not be easily generated in the type Ib diamond lattice without the addition of S. Even if the NV0 and NV− centers were generated simultaneously in the diamond lattice with the addition of 0.25 wt% S, the intensity was higher for the NV− peak than for the NV0 peak. The results of this study improve our understanding of the formation mechanisms of natural diamonds and represent an effective method for controlling the NV center in the diamond lattice.

High-pressure single-crystal/powder synchrotron X-ray diffraction was carried out on a hydrous pure magnesium pyrope (Mg 3 Al 2 Si 3 O 12 ) containing 900 ppmw H 2 O, synthesized at 4.0 GPa and 1300 K. The pressure-volume ( P - V ) single-crystal data from room pressure to 9.81 GPa at ambient temperature were fitted by a third-order Birch-Murnaghan equation of state (BM-EoS) yielding a unit-cell volume of V 0 = 1505.14 ± 0.38 A 3 , an isothermal bulk modulus of K 0 = 160 ± 3 GPa and its pressure derivative K ′ 0 = 5.2 ± 0.4. When fixing K' 0 = 4.0, the data yielded V 0 = 1504.58 ± 0.32 A 3 and K 0 = 166 ± 2 GPa. The pressure-volume-temperature ( P - V - T ) EoS of the synthetic hydrous pyrope was also measured at temperatures up to 900 K and pressures up to 16.75 GPa, using a diamond anvil cell in conjunction with in situ synchrotron angle-dispersive powder X-ray diffraction. The P - V data at room temperature and in a pressure range of 0.0001–14.81 GPa were then analyzed by a third-order BM-EoS and yielded V 0 = 1505.35 ± 0.25 A 3 , K 0 = 161 ± 2 GPa, K ′ 0 = 5.0 ± 0.3. With K' 0 fixed to 4.0, we also obtained V 0 = 1505.04 ± 0.29 A 3 and K 0 = 167 ± 1 GPa. Consequently, we fitted the P - V - T data with the high-temperature third-order BM-EoS approach and obtained the thermoelastic parameters of V 0 = 1505.4 ± 0.3 A 3 , K 0 = 162 ± 1 GPa, K ′ 0 = 4.9 ± 0.2, the temperature derivative of the bulk modulus ( ∂K 0 / ∂T ) P = −0.018 ± 0.004 GPa K −1 , and the thermal expansion coefficient at ambient conditions α 0 = (3.2 ± 0.1) × 10 −5 K −1 . These properties were consistent with the thermal pressure EoS analysis. These new results on hydrous pyrope were also compared with previous studies of anhydrous pyrope. The main effect of hydration on pyrope is to decrease K 0 and increase K' 0 by increasing the vacancies or unoccupied volume in the structure. The entire dataset enabled us to examine the thermoelastic properties of important mantle garnets and this data has further applications for modeling the P-T conditions in the upper mantle of the Earth’s interior using deep mineral assemblages.

The exploration of the vast phase space of transition metal nitrides is critical for discovering novel materials and potential technological applications. Manganese mononitride with a tetragonal structure (space group I4/mmm) was synthesized in a laser-heating diamond anvil cell, which could be quenched to ambient pressure. The bulk modulus of 173 GPa was measured using in situ high-pressure diffraction, and the axial compressibility shows that, under pressure, the a direction is much more compressible than the c direction in tetragonal MnN. DFT results with correction of the on-site repulsion (GGA + U) confirm that tetragonal MnN is energetically stable and antiferromagnetic. This study highlights the need to include on-site repulsion to understand 3d metal nitrides.

High pressure can drastically alter chemical bonding and produce exotic compounds that defy conventional wisdom. Especially significant are compounds pertaining to oxygen cycles inside Earth, which hold key to understanding major geological events that impact the environment essential to life on Earth. Here we report the discovery of pressure-stabilized divalent ozonide CaO3 crystal that exhibits intriguing bonding and oxidation states with profound geological implications. Our computational study identifies a crystalline phase of CaO3 by reaction of CaO and O2 at high pressure and high temperature conditions; ensuing experiments synthesize this rare compound under compression in a diamond anvil cell with laser heating. High-pressure x-ray diffraction data show that CaO3 crystal forms at 35 GPa and persists down to 20 GPa on decompression. Analysis of charge states reveals a formal oxidation state of −2 for ozone anions in CaO3. These findings unravel the ozonide chemistry at high pressure and offer insights for elucidating prominent seismic anomalies and oxygen cycles in Earth’s interior. We further predict multiple reactions producing CaO3 by geologically abundant mineral precursors at various depths in Earth’s mantle., Calcium and oxygen are abundant elements in the Earth’s mantle, largely present as calcium oxide. Here the authors show, by experiments and computations, that calcium ozonide (CaO3) is stabilized at the high pressures and temperatures characteristic of the lower mantle, with implications for the deep Earth’s chemistry.

Mn

The structural phase transition of synthetic ZnFe

In this paper, hydrogen-doped industrial diamonds and gem diamonds were synthesized in the Fe–Ni–C system with C10H10Fe additive, high pressures and high temperatures range of 5.2–6.2 GPa and 1250–1460°C. Experimental results indicate similar effect of hydrogen on these two types of diamonds: with the increasing content of C10H10Fe added in diamond growth environment, temperature is a crucial factor that sensitively affects the hydrogen-doped diamond crystallization. The temperature region for high-quality diamond growth becomes higher and the morphology of diamond crystal changes from cube-octahedral to octahedral. The defects on the {100} surfaces of diamond are more than those on the {111} surfaces. Fourier transform infrared spectroscopy (FTIR) results indicate that the hydrogen atoms enter into the diamond crystal lattice from {100} faces more easily. Most interestingly, under low temperature, nitrogen atoms can also easily enter into the diamond crystal lattice from {100} faces cooperated wi...

The synthesis of phosphorus and nitrogen co-doped diamond is investigated in the NiMnCo–C system by adding P 3 N 5 or carbonyl iron powders mixed with phosphorus powders under high pressure and high temperature. Experimental results show that the color distribution in diamond crystals with low concentration of P 3 N 5 additive is not uniform. The color becomes deep green with the increase of P 3 N 5 additive. The optical images and FTIR spectra reveal that the nitrogen atoms are more easily incorporated via {111} than {100} in the same conditions. In addition, the result of FTIR spectra of synthesized diamond indicates that the hydrogen atoms in the form of sp 3 –CH 2 – are more likely to enter the diamond lattice in the P/N co-doped system, compared with the single N-doped system. The absorption peak at 3107 cm − 1 attributed to vibration of H-related point defects (sp 2 –CH CH–) is observed in diamonds, which is often found in natural diamonds. The Raman shifting to lower frequency and FWHM value becoming wider are due to the doping of phosphorus atoms.

The temperature and convection fields of a catalyst with three different heights were simulated in a temperature gradient growth (TGG) system under high pressure and high temperature (HPHT) conditions. Temperature fields were simulated to rule out the influence of temperature on the crystal morphology. The features of the calculated convection field could predict the particular situations of diamond growth systems very well, and could explain the change of diamond morphology accompanying the growth process. According to the calculated results, we predict that the morphology of a diamond crystal changes from cubic crystal to cub-octahedral. A good agreement has been obtained between the calculated results and the observed experimental data. The morphology and structural properties of the synthesized samples are characterized by optical microscopy and a Raman spectrum. The results illustrate that the synthesized diamond crystals have less lattice distortion and with high quality.

The B/N co-doped diamonds have been successfully fabricated in the graphitic mixtures of C and BN system with Fe–Ni alloy as catalyst under high pressure and high temperature conditions. Morphology and structural properties of the synthesized samples are characterized by optical microscope, scanning electron microscopy and X-ray diffraction. Raman spectrum and X-ray photoelectron spectroscopy are used to confirm their chemical composition and atomic-level hybrid qualities. Our results indicate that B, C and N combined with each other and formed stable chemical bonds in B/N co-doped diamonds, and the h-BN additive played an important role in determining the morphology of diamond crystal. The B/N co-doped diamond shows strip shape elongated along the {111} direction. According to our results, the possible growth mechanism is discussed.

In this paper, we report the influence of hydrogen impurity in metal melts on the growth process, morphology, and impurity structure of diamond crystals. In a series of experiments, the hydrogen impurity in the growth system comes from the decomposition of TiH2 in the HPHT chamber. Diamond growth and morphology are also significantly influenced by the hydrogen impurity. We also note that with increasing hydrogen concentration in the synthetic system from 0.05 wt.% to 0.5 wt.%, the minimum conditions for diamond synthesis increased rapidly. The diamond growth processes are suppressed by the excessive TiH2 additive (0.2 wt.%) and some tiny diamond crystals can be detected by Raman spectroscopy. The effects of the hydrogen on the properties of the crystallization medium have been extensively studied by XRD and Raman spectra. The FTIR spectra of synthesized diamond indicate that the hydrogen atoms can enter the diamond lattice and substitute the carbon atoms in the form of sp3 CH2 .

In this paper, diamond crystallization from carbonyl nickel powders is investigated in detailed by temperature gradient growth (TGG) at high pressure (6.0–6.5 GPa) and high temperature (1350–1430 °C) conditions. We find that the synthesis condition for diamond crystallization is higher than that of the conventional Fe–Ni catalyst medium. The morphology of the diamond synthesized from carbonyl nickel powders tends to an irregular shape. Furthermore, Fourier transform infrared (FTIR) measurements indicate that nitrogen atoms simultaneously exist in the synthesized diamond in the forms of A-centers and C-centers. We hope that our paper can provide valuable information and clues to study the incorporation of nitrogen impurity into natural diamond structure.

In this paper, perfect {100}-oriented single diamonds with higher nitrogen concentration are successfully synthesized at a pressure of 5.5 GPa and temperature ranging from 1285 to 1294 °C by the adjustment of catalyst (Fe64Ni36) components. The content of carbonyl nickel powders has significant effect on the nitrogen concentration and the growth rate of the diamond crystals. Fourier transform infrared (FTIR) measurements reveal that the value of nitrogen concentration for the synthesized diamond is up to approximately 1020 ppm. Furthermore, basing on the diamond surface configuration, the structure of growth steps arranged layer by layer on {111} face is noticed using scanning electron microscopy (SEM), whereas the occurrence is not observed on {100} face.

In this paper, we investigate diamond crystallization in Fe-Ni-C with an aluminum additive and the capability of aluminum for converting graphite to diamond in a series of experiments at 4.9–5.5 GPa and 1240–1500°C. Our experimental results show that the growth habits of diamond crystal have been significantly influenced by the addition of aluminum as a catalyst. The crystal color changes from yellow to nearly colorless. The morphology of the synthesized diamond crystals gradually changes from cubic-octahedron to octahedron in the Fe-Ni-C systems with increasing aluminum additive. The lowest synthesis conditions fell first and then rose with increasing aluminum. We found a suitable addition of aluminum is very effective in lowering the synthesis conditions while an excessive aluminum additive may have a suppressive effect on the diamond nucleation.

We present the shape-controlled synthesis of strip shape diamond with stretched crystal faces along {100} or {111} direction and larger length-to-radius ratio than the conventional diamond in the designed NiFe–C system at high pressures and high temperatures (HPHT). A series of synthetic experimental results on the strip shape diamonds were obtained at different pressures and temperatures. Under the constant pressure condition, the morphology of the strip shape diamond varied with the increase of temperature obviously. Fourier transform infrared (FTIR) micro spectroscopy and Raman spectroscopy revealed that the various locations of crystal face have different nitrogen impurity concentration, and internal strain and defects in these strip shape crystals. According to these results, it can be concluded that the difference of growth rates at various crystal faces results in different crystal morphologies. Based on the growth characteristics, we suggest that composition segregation of the metal film around the growing crystal induces the formation of strip shape diamond.

A multiseed method for high quality sheet cubic diamonds synthesis by a temperature gradient method (TGM) under high pressure and high temperature (HPHT) conditions for scientific research and comm...

The discovery of electrides, in particular, inorganic electrides where electrons substitute anions, has inspired striking interests in the systems that exhibit unusual electronic and catalytic properties. So far, however, the experimental studies of such systems are largely restricted to ambient conditions, unable to understand their interactions between electron localizations and geometrical modifications under external stimuli, e.g., pressure. Here, pressure-induced structural and electronic evolutions of Ca2N by in situ synchrotron X-ray diffraction and electrical resistance measurements, and density functional theory calculations with particle swarm optimization algorithms are reported. Experiments and computation are combined to reveal that under compression, Ca2N undergoes structural transforms from R 3 ¯ m symmetry to I 4 ¯ 2d phase via an intermediate Fd 3 ¯ m phase, and then to Cc phase, accompanied by the reductions of electronic dimensionality from 2D, 1D to 0D. Electrical resistance measurements support a metal-to-semiconductor transition in Ca2N because of the reorganizations of confined electrons under pressure, also validated by the calculation. The results demonstrate unexplored experimental evidence for a pressure-induced metal-to-semiconductor switching in Ca2N and offer a possible strategy for producing new electrides under moderate pressure.

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.

The effect of the catalyst height on the morphology of diamond crystal is investigated by means of temperature gradient growth (TGG) under high pressure and high temperature (HPHT) conditions with using a Ni-based catalyst in this article. The experimental results show that the morphology of diamond changes from an octahedral shape to a cub-octahedral shape as the catalyst height rises. Moreover, the finite element method (FEM) is used to simulate the temperature field of the melted catalyst/solvent. The results show that the temperature at the location of the seed diamond continues to decrease with the increase of catalyst height, which is conducive to changing the morphology of diamond. This work provides a new way to change the diamond crystal morphology.

To investigate the effect of the hydrogen element on diamond crystallization, hydrogen doped diamond crystals are synthesized at 5.0–6.0 GPa and 1250–1600 °C by adding ferrocene (C10H10Fe) to a system of carbon and Fe-based solvent–catalyst. The essential dependence of diamond morphology and nucleation on the composition of the crystallization medium is established in the P–T diagram. It is found that the growth region of the {111} face becomes wider, while the region of the {100} face becomes narrower and almost disappears with increasing concentration of C10H10Fe. The changing of the diamond growth habits can be explained by the effect of hydrogen from the decomposition of C10H10Fe on diamond crystallization. Fourier transform infrared absorption spectra reveal that the hydrogen-related peaks increase with an enhancement in the ratio of C10H10Fe additive. The observed Raman shift is due to the doping of hydrogen atoms into the diamond lattice. In addition, we find that the change of characteristics of the growth medium of the diamond crystal induced by hydrogen is an important factor for the changes of the synthesis conditions, the growth rate and the nitrogen concentration of the synthesized diamond.

We investigate the temperature field variation in the growth region of a diamond crystal in a sealed cell during the whole process of crystal growth by using the temperature gradient method (TGM) at high pressure and high temperature (HPHT). We employ both the finite element method (FEM) and in situ experiments. Simulation results show that the temperature in the center area of the growth cell continues to decrease during the process of large diamond crystal growth. These results are in good agreement with our experimental data, which demonstrates that the finite element model can successfully predict the temperature field variations in the growth cell. The FEM simulation will be useful to grow larger high-quality diamond crystal by using the TGM. Furthermore, this method will be helpful in designing better cells and improving the growth process of gem-quality diamond crystal.

In this paper, we explore diamond synthesis with a series of experiments using an Fe—Ni catalyst and a P3N5 additive in the temperature range of 1250–1550 °C and the pressure range of 5.0–6.3 GPa. We also investigate the influence of nitrogen on diamond crystallization. Our results show that the synthesis conditions (temperature and pressure) increase with the amount of P3N5 additive increasing. The nitrogen impurity can significantly influence the diamond morphology. The diamonds stably grow into strip and lamellar shapes in the nitrogen-rich environment. The Fourier-transform infrared spectrum shows that the nitrogen concentration increases rapidly with the content of P3N5 additive increasing. By spectrum analysis, we find that with the increase of the nitrogen concentration, the Ib-type nitrogen atoms can aggregate in the A-centre form. The highest A-centre nitrogen concentration is approximately 840 ppm.

We attempted to generate ultrahigh pressure and temperature simultaneously using a multi-anvil apparatus by combining the technologies of ultrahigh-pressure generation using sintered diamond (SD) anvils, which can reach 120 GPa, and ultrahigh-temperature generation using a boron-doped diamond (BDD) heater, which can reach 4000 K. Along with this strategy, we successfully generated a temperature of 3300 K and a pressure of above 50 GPa simultaneously. Although the high hardness of BDD significantly prevents high-pressure generation at low temperatures, its high-temperature softening allows for effective pressure generation at temperatures above 1200 K. High temperature also enhances high-pressure generation because of the thermal pressure. We expect to generate even higher pressure in the future by combining SD anvils and a BDD heater with advanced multi-anvil technology.