This study employs a domestically produced large-volume cubic high-pressure apparatus (SPD-6 & times; 1200) to simulate high-temperature and high-pressure conditions and synthesizes slab shape diamond single crystals in the Fe-Ni-C-Si system. The influence of varying silicon doping levels on diamond morphology and quality was systematically investigated. The results demonstrate that silicon is successfully incorporated into the diamond lattice through bonding. As the doping concentration increases, the size of the diamond single crystals decreases significantly, the crystal surface becomes rough, and defects emerge. Concurrently, the internal stress of the diamond increases while its quality deteriorates, as confirmed by shifts in the diamond Raman peak. Furthermore, infrared spectroscopy characterization reveals that nitrogen within the silicon-doped diamond exists in the form of single atoms (C-center). During synthesis, silicon interacts with nitrogen; with increasing silicon content, the nitrogen content inside the diamond gradually decreases. This work provides insights into the growth mechanism of natural silicon-containing diamonds and expands the application potential of silicon-doped diamond single crystals.

Biomass gasification shows potential to produce green fuels, i.e. green methanol. Cost-effective and deep removal of biomass tar is vital, but is still a bottleneck issue. In this study, photothermal catalytic reforming (PCR) was proposed for deep removal of tar. Different co-doped TiO2 photothermal catalysts were prepared by sol-gel method. The co-doped of Ni and N improved the optical absorption and electron-hole separation properties of the catalysts, and promoted more photoinduced charge carrier generation to participate in the reaction. Characterizations and density functional theory (DFT) calculations indicated Ni and N atoms induced the local charge redistribution and formed a unique charge-polarized surface. The Ni sites on the catalyst surface were activated which successfully achieved the photothermal synergistic effect and strengthened the creaking of tar. Accordingly, tar conversion ratio reached 100 % at 500 degrees C and was maintained for 10 h with a significantly inhibition of carbon deposition. Furthermore, a biomass gasification towards green methanol scenario was built, and different tar removal technologies, including PCR, partial oxidation, catalytic creaking, were compared. It was found PCR matches well for the deep removal condition without external heating, and can improve the hydrogen content in syngas, which improves the overall conversion efficiency and brings higher economic benefits. This work achieves thorough conversion of tar at low temperature, and provides insight for the design of high-efficient photothermal catalyst to help biomass utilization move into a new stage of high-value chemical synthesis.

Boron-doped diamond (BDD) is highly valued for its excellent semiconductor properties, but high boron doping levels often cause lattice distortion and degraded electrical performance. To address this challenge, boron-oxygen (B-O) co-doping was employed to synthesize high-quality single crystals by a high pressure and high temperature (HPHT) method in the Fe-Ni-C system (5.8-6.2 GPa, 1360-1440 degrees C). Using amorphous boron and Fe3O4 as dopant sources, crystals with gradient boron concentrations were characterized by FTIR, Raman, XRD, XPS, EPMA and Hall effect measurements. Results confirmed successful B and O incorporation, with oxygen mitigating boron-induced stress. The sample with 5 wt% B and 5 wt% Fe3O4 achieved optimal electrical performance: a carrier concentration of 3.76 & times; 1018 cm-3 and a resistivity of 8.15 & times; 10-1 Omega cm. Compared to pure BDD, B-O co-doping enhanced carrier mobility and reduced resistivity due to improved crystalline quality. This work provides experimental support for optimizing co-doping processes and advancing high-performance semiconductor diamond materials.

Nitrogen is one of the primary impurities in synthetic diamond. Among these impurity-related defects, the nitrogen-vacancy (NV) center exhibits unique quantum and physical properties. These characteristics render it a critical platform for advanced scientific research and diverse technological applications. Nevertheless, the direct synthesis of type Ib diamond containing exclusively NV- color centers remains a critical challenge for quantum technology applications. In this study, high-nitrogen-content diamond single crystals with dominant NV- color centers were successfully synthesized in the Fe-Ni-C system via the powder catalyst method under high-pressure and high-temperature (HPHT) conditions, utilizing g-C3N4 as a novel nitrogen source. The morphology, bonding configuration, nitrogen aggregation forms, and photoluminescence properties of the synthesized crystals were systematically investigated. With increasing g-C3N4 addition, the color of the synthesized diamond transitioned progressively from yellow-green to green, and ultimately to dark green at the highest addition level. X-ray photoelectron spectroscopy (XPS) confirmed that nitrogen atoms were successfully incorporated into the diamond lattice through chemical bonding. Fourier-transform infrared (FTIR) spectroscopy revealed that the nitrogen content within the diamond increased progressively as the g-C3N4 addition increased. The appearance of characteristic absorption peaks verified that the synthesized crystals were type Ib diamond. Photoluminescence (PL) spectra demonstrated that the synthesized crystals were free of NV0 color centers. However, the NV luminescence gradually diminished with increasing nitrogen content. Raman spectroscopy confirmed that the quality of the synthesized crystals progressively declined with increasing g-C3N4 addition. This work establishes g-C3N4-mediated HPHT synthesis as a promising one-step strategy for fabricating quantum-grade NV--enriched diamonds.

This study systematically investigates the effect of synthesis pressure on the characteristics of diamond crystals grown by the high temperature and high pressure (HPHT) method in a boron-nitrogen co-doping system. Diamond single crystals were synthesized within a pressure range of 5.7-6.5 GPa using a NiMnCo alloy as the catalyst, with simultaneous introduction of nitrogen and boron sources. Comprehensive characterization was performed using Fourier-transform infrared (FTIR) and Raman spectroscopies. The results show that pressure is a key parameter for tuning the competitive doping between boron and nitrogen. As the pressure increases from 5.7 GPa to 6.5 GPa, the nitrogen content in diamond decreases significantly while the incorporation efficiency of boron is markedly enhanced. This is directly reflected in the co-doped crystals by a gradual fading of the macroscopic green color with increasing pressure, and the FTIR results further confirm this conclusion. Raman spectroscopy further reveals that increasing pressure under co-doping conditions helps improve crystal quality, as evidenced by a reduction in the full width at half maximum (FWHM) of the characteristic diamond peak. Moreover, pressure variation does not introduce new types of luminescent defects; the main luminescence in all samples originates from NV- color centers. This study finds that increasing the system pressure promotes boron incorporation while suppressing nitrogen uptake. This provides key experimental evidence for the targeted tuning of diamond semiconductor properties (e.g., the fabrication of p-type semiconductors) via HPHT process parameters, and also offers valuable insights for understanding the mantle origin of natural diamonds.

Macroscopic and microscopic defect control in diamonds is a key research area in both diamond synthesis and its applications. High-nitrogen diamonds have received significant attention in both research and industry owing to their unique properties, which result from nitrogen impurities. Therefore, the preparation of high-quality high-nitrogen diamonds has emerged as a focal point of interest in recent years. This study thoroughly analyzed the causes of local burrs in high-nitrogen diamonds synthesized with the NiMnCo catalyst and introduced corresponding strategies to address this issue. Optical microscopy, scanning electron microscopy, Fouriertransform infrared spectroscopy, and X-ray diffraction results reveal that on the one hand, the burr is caused by the complex effect of the interaction of hard phase particles (such as MnO) and fluid-rich growth media with carbon and metal catalyst melt. On the other hand, during cooling, the hard phase (such as MnO) generated in the metal catalyst melt rich in highly saturated C-N-H-O fluid precipitates out. The destruction of diamond surface morphology. Raman spectroscopy and X-ray photoelectron spectroscopy results indicate that the use of the FeNi catalyst in diamond synthesis prevents burr formation and effectively reduces residual stress. Additionally, increasing synthesis pressure and applying hydrogen doping can further reduce burrs and residual stress in the diamond.

Expression of concern for ‘Preparation of “natural” diamonds by HPHT annealing of synthetic diamonds’ by Xiaopeng Jia et al., CrystEngComm, 2018, 20, 505–511, https://doi.org/10.1039/C7CE02013A.

SrTiO3 (STO) is a highly stable and inexpensive perovskite oxide thermoelectric, but phase-pure STO has a low electrical conductivity and high thermal conductivity. This overall poor thermoelectric performance limits its use as a high-temperature thermoelectric. Therefore, suitable methods are needed to enhance the electrical conductivity and reduce the thermal conductivity of STO materials. Compositing STO with materials with a higher conductivity is the most direct way to improve the thermoelectric properties of STO. This paper uses the high pressure and high temperature (HPHT) synthesis method to create an STO composite with Nb to improve the electrical properties. NbN is used to create pores to prepare composite thermoelectric ceramics. Nb in the sample was oxidized to various niobium oxides with thermoelectric properties using HPHT synthesis, and N2 generated during the synthesis of NbN produced pores in the material, which reduced its thermal conductivity and optimized the thermoelectric properties of STO. When the amount of NbN added is x = 0.03, the maximum zT value of 0.295 is obtained at 973 K. This paper provides a method to reduce the thermal conductivity of STO materials to improve their thermoelectric properties by creating voids with NbN during HPHT synthesis.

In oxide thermoelectrics, controlling phonon transport is crucial for reducing lattice thermal conductivity.In this work, we report the synthesis of a series of high-entropy perovskite ceramics with the composition (Sr0.6La0.2Ca0.1Eu0.1)(Ti0.6-xNb0.2Hf0.1Zrx)O3, using a combined high-pressure high-temperature (HPHT) and high-energy ball milling (HEBM) process. This multistep route constructs a hierarchical phonon scattering network from the atomic to nanoscale. We find that the sample with Zr content x = 0.09 exhibits the lowest lattice thermal conductivity of 0.89 W m-1 K- 1 at 873 K, representing a substantial reduction compared to undoped SrTiO3. The suppression of thermal conductivity is attributed to synergistic phonon scattering mechanisms, including pointdefect scattering from mass and bonding fluctuations, grain boundary scattering from nanoscale refinement, and enhanced Umklapp scattering due to lattice anharmonicity, as confirmed by TEM analysis and Gr & uuml;neisen parameter calculations. The incorporation of high-entropy A- and B-site dopants induces local structural disorder and stress fields, further promoting phonon incoherence. This study demonstrates that coupling high-entropy chemical disorder with pressure-driven microstructure control enables effective decoupling of phonon transport pathways. The approach offers a promising strategy for designing next-generation oxide thermoelectric materials with intrinsically low lattice thermal conductivity and robust structural integrity.

In this paper, we report the synthesis of phosphorus-doped diamond using the China-type large volume cubic high-pressure apparatus under the Fe-C-P system with Fe3P added using Fe as a catalyst at 6 GPa and 1400-1500 degrees C. The characterization results show that the increase in Fe3P addition not only causes pits and growth streaks on the crystal surface. But also leads to an increase in the internal stress of the crystals and also decreases the crystallinity of the crystals. With the increase of Fe3P addition, the C-center nitrogen content increases slowly, but the whole C-center nitrogen content remains at a low level. Phosphorus atoms enter the diamond lattice to form P-C and P-O bonds with C and O. The synthesized crystals have n-type conductivity with resistivity up to 8.09 x 105 and Hall's coefficient of -8.82 x 108. It has been demonstrated that Fe as a catalyst is beneficial for the synthesis of diamond crystals with higher quality and can effectively reduce the entry of impurities into the synthesis system. Comparison of the performance of diamond synthesized with different additives demonstrated that phosphides are better additives for synthesizing n-type semiconductor diamonds. The Fe-C-P system constructed by adding Fe3P to Fe as catalyst is suitable for the synthesis of n-type semiconducting diamonds. This study provides insights into the construction of novel systems for synthesizing n-type semiconducting diamonds and emphasizes the important influence of additives and catalyst selection on diamond properties.

Bisphenol A (BPA) is a hazardous pollutant in industrial wastewater, whose safe disposal remains a worldwide problem. This paper explored the potential of aqueous phase reforming (APR) towards the treatment and H2 generation of concentrated BPA wastewater over Pt/C and Ni-based catalysts supported by Al2O3, C, and ZSM-5. It was demonstrated that Ni/Al2O3 outperformed Ni/C and Ni/ZSM-5 in chemical oxygen demand (COD) removal and H2 production, which could be attributed to its high medium basic sites and large pore volume. In addition, the H2 yield over Ni/Al2O3 (21.93 mmol H2/g COD) was even higher than that over Pt/C (3.51 mmol H2/g COD). The optimal COD removal and H2 yield over Ni/Al2O3 reached 88.09% and 250.97 mmol/g COD H2 was obtained at 340 degrees C for 4 h. According to the identified reactants and previous research, the reaction pathway for APR of BPA over Ni/Al2O3 involved the cleavage of the C-C bond of BPA to generate phenol and p-iso- propylphenol, with Bis-(4-hydroxyphenyl)-methane formed concurrently through the demethylation of BPA.

Electrides, characterized by spatially confined anionic electrons, have emerged as a promising class of materials for catalysis, magnetism, and superconductivity. However, transition-metal-based electrides with diverse electron dimensionalities remain largely unexplored. Here, we perform a comprehensive first-principles investigation of Y-Co electrides, focusing on Y3Co, Y3Co2, and YCo. Our calculations reveal a striking dimensional evolution of anionic electrons: from two-dimensional (2D) confinement in YCo to one-dimensional (1D) in Y3Co2 and zero-dimensional (0D) in Y3Co. Remarkably, the YCo monolayer exhibits intrinsic ferromagnetism, with a magnetic moment of 0.65 mu B per formula unit arising from spin-polarized anionic electrons mediating long-range coupling between Y and Co ions. The monolayer also shows a low exfoliation energy (1.66 J/m2), indicating experimental feasibility. All three electrides exhibit low work functions (2.76 eV-3.11 eV) along with Co-centered anionic states. This work expands the family of transition-metal-based electrides and highlights dimensionality engineering as a powerful strategy for tuning electronic and magnetic properties.

Thermoelectrics (TE) have received a lot of attention for their ability to directly convert heat into electricity. This capability provides a promising solution for waste heat recovery and clean energy utilization. Strontium titanate (SrTiO3) is a promising N-type oxide TE material. However, its practical application is limited by low electrical conductivity and high thermal conductivity. Here, we present a high-pressure synthesis technique aimed at simultaneously introducing defects as well as enhancing phonon scattering. Enhancing the thermoelectric properties of strontium titanate thermoelectric materials. SrTiO3 samples doped with different concentrations of La were synthesized by high-pressure high-temperature (HPHT) synthesis, which effectively promotes the solidphase reaction and thus allows for a more homogeneous and efficient doping of La atoms into the SrTiO3 lattice as compared to the conventional synthesis method. The introduction of La3+ creates a charge imbalance, which is compensated by the formation of oxygen vacancies. These oxygen vacancies act as donor defects, which in turn increase the carrier concentration and significantly improve the electrical conductivity of the samples. At the same time, the HPHT synthesis conditions induced severe lattice distortions, leading to grain refinement and the formation of dislocation networks and nanopores. By modulating the density and distribution of multiscale defects, La doping significantly improves the interfacial phonon scattering efficiency. This condition reduces the thermal conductivity and improves the thermoelectric properties. By combining defect engineering and interfacial phonon scattering, we achieved the decoupling of electrical and thermal transport properties in La-doped SrTiO3. Consequently, the thermoelectric figure of merit (zT) was significantly enhanced, reaching 0.18 at 973 K. This study introduces a new methodology and theoretical foundation for the development of high-performance oxide TE materials.

Natural diamond inclusions comprise elements such as carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), which can be assumed to exist in the natural diamond growth environment. Therefore, the artificial construction of the C-H-O-N system plays an important role in exploring the growth mechanism of natural diamonds. Herein, diamond crystals were successfully synthesized in the NiMnCo-C system by adding carbohydrazide (CH6N4O) as the organic additive at 1280 to 1320 degrees C and 5.4 GPa-6.0 GPa. The crystals were characterized using various analytical tools. Optical microscopy (OM) showed that the additive caused new extended defects similar to different dislocations. These filiform defects mainly appeared inside the top {111} face of the synthesized diamond and were always perpendicular to the {111} face. Raman spectroscopy and X-ray diffraction (XRD) analysis indicated that the synthesized diamond had high-quality sp3 structures. The Fourier transform infrared spectroscopy (FTIR) spectra showed that under a constant doping concentration, the N content inside the diamond increased with increasing synthesis temperature and constant pressure but decreased with increasing synthesis pressure and constant temperature. X-ray photoelectron (XPS) spectroscopy confirmed that N, O, and H successfully entered the diamond lattice.

In this study, a combination of theoretical calculations and experiments were carried out to analyze boron phosphide materials. Amorphous boron powder and amorphous red phosphorus were used as raw materials to directly synthesize the target samples in one step under high-pressure and high-temperature (HPHT) conditions. Theoretical calculations were then carried out based on the XRD spectra of boron phosphide at 4 GPa and 1200 °C. The experimental results show that the target samples can be successfully prepared at HPHT. The electrical properties of the samples were characterized, and it was found that their conductivity increased with the increase in temperature, and they have a semiconducting nature, which is consistent with the theoretical calculations. Its Seebeck coefficient is positive at different temperatures, indicating that the synthesized boron phosphide is a P-type semiconductor. The combination of theoretical calculations and experiments shows that high pressure can reduce the lattice constant of boron phosphide, thus reducing its forbidden bandwidth, which improves its electrical properties. EDS shows a homogeneous distribution of the elements in the samples. Successful synthesis of BP crystals will probably stimulate more research into its semiconductor properties. It may also provide some assistance in the application of BP in aero-engine high-temperature monitoring systems as well as thermally controlled coatings for deep-space probes.

Synthesis and properties of n-type semiconducting diamonds with TiP addition in the FeNi–C system under HTHP conditions.

In this work, we used finite element simulations to study the changes in the temperature field and convection field inside the cavity during diamond growth. The simulations revealed that the temperature around the diamond first decreases and then increases as the diamond grows. This is because diamond has a high thermal conductivity, and as the diamond grows, the diamond absorbs the surrounding heat, causing the temperature around the diamond to decrease. The location of the cylindrical catalyst (CYC) has a higher temperature, and as the diamond grows to a certain height, the diamond transfers the heat from CYC downward, which can cause the temperature at the bottom to rise. We then simulated the convection field during diamond growth and found that the convection velocity of CYC accelerated as the crystal grew. This will speed up the growth of the crystals, but too much speed will degrade the quality of the crystals. We then simulated the variation of the convection and temperature fields of the convex catalyst (COC). We found that the temperature and convection velocity of COC are less affected by the diamond on the cavity compared to the CYC. Moreover, when using COC in growing large-size diamonds, the convection velocity of the catalyst is more stable and it is easier to grow high-quality large single crystals. This work provides some theoretical reference for diamond growth.

The tar problem is a bottleneck issue of biomass gasification. The influence of anaerobic digestion on gasification tar formation is still unclear. In this work, the influence of the degree of anaerobic digestion on physicochemical properties of the digestate were investigated, and consequently on tar yield and distribution. The content of cellulose exhibits the most critical parameter affecting tar yield. Minimum tar yields (2.5 wt%, 1.9 wt% and 1.6 wt% for pyrolysis, CO2 gasification and H2O gasification) was obtained in day 9 with a maximum lignin content (29.5 wt%) and a minimum cellulose content (24.8 wt%). Both gasification agent of CO2 and H2O significantly reduce tar yields. The tar distribution was always dominated by benzofuran, 2,3-dihydro- and phenol derivatives regardless of the agent. This work provides in-depth insights and clarifies the tar formation characteristic of the integrated process, which helps to realize the efficient and green conversion of biomass.