High-pressure Synthesis Research Articles

High-pressure high-temperature synthesis of NdRe2.

In this study, we report the synthesis of a new cubic neodymium-rhenium metallic alloy NdRe2 through the utilization of high pressure and laser heating in a diamond anvil cell. NdRe2 crystallizes in the space group with a lattice parameter equal to 7.486 (2) Å and Z = 8at 24 (1) GPa and 2,200 (100) K. It was studied using high-pressure single-crystal X-ray diffraction. The compound crystallizes in the cubic MgCu2 structure type. Its successful synthesis further proves that high-pressure high-temperature conditions can be used to obtain alloys holding a Laves phase structure. Ab initio calculations were done to predict the mechanical properties of the material. We also discuss the usage of extreme conditions to synthesize and study materials present in the nuclear waste.

Pressure-induced superconductivity in hypercoordinated 5p-block element nitrides MN6 (M = Sb, Te, I)

The recent studies of high-pressure synthesis and stabilization of a variety of polynitrogens have had an immense impact on nitrogen chemistry. However, the metallization and superconductivity of solid nitrogen at high pressure have not yet been verified. Here, based on first-principles calculations, we report a remarkable finding of the metallic N6 hexazine ring stabilized in the 5p -block element nitrides MN6 (M = Sb, Te, I) at an experimentally accessible pressure of 100 GPa. Strikingly, the 5p -block elements act as precompressors and electron donors for the N sublattice, leading to the Jahn-Teller distortion of the N6 hexazine ring and endowing the 5p -block element nitrides superconductivity with a high superconducting critical temperature (T c) of up to 36.8 K, close to the McMillan limit (40 K). This is the first discovery of a nitrogen-based superconductor with distorted N6 hexazine rings. The high T c is attributed to the strong electron-phonon coupling that is induced by the phonon softening and the hybridized electronic states between N and 5s and 5p orbitals of 5p -block elements. Our works have broad implications for enriching novel p -block element nitrides and nitrogen chemistry under extreme conditions.

High-pressure Synthesis of Cobalt Polynitrides: Unveiling Intriguing Crystal Structures and Nitridation Behavior.

In this study, we conduct extensive high-pressure experiments to investigate phase stability in the cobalt-nitrogen system. Through a combination of synthesis in a laser-heated diamond anvil cell, first-principles calculations, Raman spectroscopy, and single-crystal X-ray diffraction, we establish the stability fields of known high-pressure phases, hexagonal NiAs-type CoN, and marcasite-type CoN2 within the pressure range of 50-90 GPa. We synthesize and characterize previously unknown nitrides, Co3N2, Pnma-CoN and two polynitrides, CoN3 and CoN5, within the pressure range of 90-120 GPa. Both polynitrides exhibit novel types of polymeric nitrogen chains and networks. CoN3 feature branched-type nitrogen trimers (N3) and CoN5 show π-bonded nitrogen chain. As the nitrogen content in the cobalt nitride increases, the CoN6 polyhedral frameworks transit from face-sharing (in CoN) to edge-sharing (in CoN2 and CoN3), and finally to isolated (in CoN5). Our study provides insights into the intricate interplay between structure evolution, bonding arrangements, and high-pressure synthesis in polynitrides, expanding the knowledge for the development of advanced energy materials.

High-pressure synthesis and magnetic characterization of quadruple perovskites SmA′3Co4O12 (A′ = Cu, Mn)

In this study, two novel quadruple perovskite compounds SmA′3Co4O12 (A′ = Cu, Mn) were synthesized using a high-pressure synthesis method. Structural analysis of the perovskites using synchrotron X-ray powder diffraction revealed that both SmCu3Co4O12 and SmMn3Co4O12 have cubic Im3‾ structure. In the temperature range of 2–300 K, SmCu3Co4O12 did not exhibit a magnetic phase transition, whereas SmMn3Co4O12 exhibited a paramagnetic to ferrimagnetic phase transition at ∼90 K. A comparison of structural information, X-ray absorption near edge structure, and magnetic properties revealed that the low-spin state (S = 0) characterizes the spin state of Co3+ when the A′ site is occupied by Cu3+. However, when the A′ site is occupied by Mn3+, the Co3+ spin state is in a high-spin state (S = 2), indicating that a long-range magnetic phase transition occurs owing to the magnetic interaction between the Mn and Co ions.

Enhanced thermoelectric properties of Mg2Si0.3Sn0.7 via Bi-doping under high pressure

A series of n-type Mg2(Si0.3Sn0.7)1-xBix compounds with 0≤x≤0.02 were successfully synthesized through a combined approach involving solid-state reaction, high-pressure synthesis, and spark plasma sintering techniques. The method yielded homogeneously distributed single-phase materials at the micron scale, although minor compositional variations were detected within nanoscale precipitates embedded in the grains. The sample with Bi content of 0.01 exhibited enhanced thermoelectric properties, reaching a peak thermoelectric figure of merit (ZT) of 1.45 at 700 K while maintaining an average ZT of about 1.1 over the temperature range of 300−773 K. The enhancement in thermoelectric performance is ascribed to the optimized carrier concentration, band convergence, and refined microstructure. The findings suggest a simplified approach to doping that could be beneficial in creating high-performance thermoelectric materials for energy conversion.

High-Pressure Synthesis of Semiconducting PbCu3Mn4O12 with Near-Room-Temperature Ferrimagnetic Order.

A transition-metal oxide of PbCu3Mn4O12 was prepared at 1523 K and 10 GPa. An A-site-ordered quadruple perovskite structure with the space group Im3̅ is assigned for this compound. Based on bond-valence-sum calculations and X-ray absorption spectroscopy, the charge combination is determined to be PbCu32+Mn44+O12. Due to Cu2+(↑)-Mn4+(↓) antiferromagnetic coupling, a near-room-temperature ferrimagnetic phase transition is observed at approximately 287 K. PbCu3Mn4O12 exhibits a semiconducting electric transport property with the energy band gap Eg ≈ 0.2 eV. In addition, considerable low-field magnetoresistance effects are observed at lower temperatures. This study provides an intrinsic near-room-temperature ferrimagnetic semiconductor that exhibits potential applications in next-generation spintronic devices.

Effect of impurity phase and high-pressure synthesis on the superconducting properties of CaKFe4As4

AeAFe4As4 (Ae = Ca, A = K; 1144) having a transition temperature of 35 K is a stoichiometric family of iron-based superconductors (FBS). Here, we present a detailed study of a high-pressure synthesis of CaKFe4As4 bulks to investigate the impact of these conditions on the superconducting properties of the 1144 family. Additionally, these samples are also prepared by conventional synthesis method at ambient pressure (CSP) and studied the influence of impurities on the superconducting properties of CaKFe4As4. Structural, microstructural, transport and magnetization measurements have been performed to reach the final conclusions. Interestingly, the high-pressure synthesis of the parent CaKFe4As4 compound enhances the transition temperature (Tc) by 2 K and the critical current density (Jc) by one order of magnitude in the whole magnetic field range of 9 T than that of the 1144 bulks prepared by CSP. It suggests the improvement of the pinning centers and grain connections by the high-pressure synthesis approach. Interestingly, our results depict the superconducting onset transition temperature (Tconset) of this stoichiometric 1144 family is robust with the presence of the common 122 (CaFe2As2 or KFe2As2) impurity phases, which is a different behavior compared to other FBS families. However, these impurity phases reduce the grain connections and lead to the phase separation during the formation of the superconducting (1144) phase.

Preparation of High-Performance Mn-Doped SnTe Materials at High Pressure and High Temperature.

SnTe is an environmentally friendly medium-temperature thermoelectric material, but its inherent low power factor (PF) and high lattice thermal conductivity severely limit its application. In this study, based on the fact that Mn doping can induce band convergence, the high-pressure and high-temperature (HPHT) synthesis method was used to optimize the sample preparation and shorten the synthesis cycle to 30 min. The results show that the Sn0.93Mn0.10Te sample achieves the maximum PF value of 34.00 μW cm-1 K-2 at 775 K and PFave value of 21.36 μW cm-1 K-2 between 300-875 K. Microstructure analysis shows that the high-pressure synthesis method introduces abundant grain boundaries, various grain sizes, multiple defects, and pore structures into the sample. These microscopic crystal structures can effectively scatter phonons and lower the lattice thermal conductivity. The modification of these micromorphologies results in the Sn0.92Mn0.11Te sample attaining a minimum lattice thermal conductivity of 0.45 W m-1 K-1 at 625 K. The thermoelectric figure of merit (zT) of sample Sn0.92Mn0.11Te reaches a maximum value of 1.1 at 775 K, and the zTave reaches 0.63 in the range of 300-875 K. This study indicates that the synergistic effect of Mn element doping and microstructure modification can effectively optimize the thermoelectric transport performance of SnTe materials.

Improvement of thermoelectric properties of xNb:(1-x)SrTiO3 composite ceramics by high-pressure high-temperature synthesis

The high stability and low cost are considered comparative advantages of the SrTiO3 chalcogenide oxide thermoelectric material. However, the pure SrTiO3 material is characterized by low electrical conductivity and high thermal conductivity, which could eventually lead to poor overall thermoelectric performance, and limit its application in the field of high temperature thermoelectricity. The development of composite-based metal materials with SrTiO3 by using suitable methods is arising as the most promising approach to improve their electrical properties. Along these lines, in this work, xNb: (1-x) SrTiO3 composite ceramics were successfully synthesized by using the high temperature and high-pressure (HPHT) method. The Nb powder was oxidized into various niobium oxides exhibiting their own thermoelectric properties under HPHT conditions to optimize the thermoelectric properties of the Nb/SrTiO3 composites. From our analysis, it was demonstrated that with the increase of the Nb powder content, the electrical properties were significantly improved. In addition, the fabricated Nb/SrTiO3 composite ceramics possessed a special “pore” microstructure, which significantly reduced the thermal conductivity of the material. In this work, the physical phase, microscopic morphology, and thermoelectric properties of the synthesized samples were also systematically tested and analyzed, and the maximum zT value of 0.28@973 K was obtained for the final sample with x = 0.4. The implementation of the HPHT method for the preparation of chalcogenide oxide composite ceramics provides valuable insights for the improvement of their thermoelectric properties.

Stabilization of Pr4+ in Silicates─High-Pressure Synthesis of PrSi3O8 and Pr2Si7O18.

The reaction between PrO2 and SiO2 was investigated at various pressure points up to 29 GPa in a diamond anvil cell using laser heating and in situ single-crystal structure analysis. The pressure points at 5 and 10 GPa produced Pr2III(Si2O7), whereas Pr4IIISi3O12 and Pr2IV(O2)O3 were obtained at 15 GPa. Pr4IIISi3O12 can be interpreted as a high-pressure modification of the still unknown orthosilicate Pr4III(SiO4)3. PrIVSi3O8 and Pr2IVSi7O18 that contain praseodymium in its rare + IV oxidation state were identified at 29 GPa. After the pressure was released from the reaction chamber, the Pr(IV) silicates could be recovered, indicating that they are metastable at ambient pressure. Density functional theory calculations of the electronic structure corroborate the oxidation state of praseodymium in both PrIVSi3O8 and Pr2IVSi7O18. Both silicates are the first structurally characterized representatives of Pr4+-containing salts with oxoanions. All three silicates contain condensed networks of [SiO6] octahedra which is unprecedented in the rich chemistry of lanthanoid silicates.

Cationic order-related magnetoresistivity and half-metallicity in bulk Pb2FeMoO6 grown by high pressure synthesis

We investigate the electric properties of Pb2FeMoO6 (PFMO), a double perovskite that can be grown in a bulk pure phase only via High Pressure/High Temperature solid-state reaction. The as-obtained PFMO is characterized by a high degree of cationic ordering at the B site between Fe3+ and Mo5+ and a ferrimagnetic transition with TN around 275 K. A semi-metallic to half-metallic transition seems to occur when the ferrimagnetic order arises thanks to the localization of a minority fraction of electrons on the Mo site. In this thermal regime, the system displays asymmetric magneto-resistivity, with selective-polarized carriers promoted by intense negative magnetic fields applied across the Néel transition during the cooling ramp. This cation-ordering related feature vanishes when the Mo-O bond length stabilizes, indicating a strong connection between the magnetic and electrical properties of this compound.

A Computational Characterization of CH4@C60

The recently synthetically prepared endohedral CH4@C60 was characterized here using calculations—namely its structure, energetics, thermodynamics, and vibrational spectrum. The calculations were carried out with DFT (density-functional theory) methods, namely by the DFT M06-2X functional and MP2, as well as B2PLYPD advanced correlated, treatments with the standard 6-31++G** and 6-311++G** basis sets, corrected for the basis set superposition error evaluated using the approximative Boys–Bernardi counterpoise method. The symmetry of the endohedral obtained in the geometry optimizations was tetrahedral T. The energetics of CH4 encapsulation into C60 was attractive (i.e., with a negative encapsulation-energy term), producing a substantial energy gain of −13.94 kcal/mol at the most advanced computational level, B2PLYPD/6-311++G**. The encapsulation equilibrium constants for CH4@C60 were somewhat higher than previously found with the CO@C60 system. For example at 500 K, the encapsulation equilibrium constant for CH4@C60 had a value one order of magnitude larger than for CO@C60. The encapsulation thermodynamic characteristics suggest that high-pressure and high-temperature synthesis could in principle also be possible for CH4@C60.

Multiscale Length Structural Investigation and Thermoelectric Performance of Double-Filled Sr0.2Yb0.2Co4Sb12: An Exceptional Thermal Conductivity Reduction by Filler Segregation to the Grain Boundaries.

Among thermoelectric materials, skutterudites are the most prominent candidates in the mid-temperature range applications. In the multiple-filled Sr0.2Yb0.2Co4Sb12 skutterudite, with Sr and Yb as fillers, we have enhanced the thermoelectric performance of CoSb3 through the reduction of lattice thermal conductivity and the optimization of carrier concentration and electrical conductivity. The high-pressure synthesis of the double-filled derivative promotes filling fraction fluctuation. This is observed by high angular resolution synchrotron X-ray diffraction, showing a phase segregation that corresponds to an inhomogeneous distribution of the filler atoms, located at the 2a positions of the cubic space group Im3̅. In addition, scanning transmission electron microscopy (STEM) combined with EELS spectroscopy clearly shows a segregation of Sr atoms from the surface of the grains, which is compatible with the synchrotron X-ray powder diffraction results. Mean square displacement parameters analysis results in Einstein temperatures of ∼94 and ∼67 K for Sr and Yb, respectively, and a Debye temperature of ∼250 K. The strong effect on resonant and disorder scattering yields a significantly lower lattice thermal conductivity of 2.5 W m-1 K-1 at 773 K. Still, good weighed-mobility values were obtained, with high filling fraction of the Yb and Sr elements. This drives a reduced electrical resistivity of 2.1 × 10-5 Ω m, which leads to a peak zT of 0.26 at 773 K. The analysis and results performed for the synthesized (Sr,Yb)-double filled CoSb3, shed light on skutterudites for potential waste-heat recovery applications.

High-pressure synthesis of a ternary yttrium-sulfur hydride superconductor with a high Tc of approximately 235 K

High-pressure synthesis of a ternary yttrium-sulfur hydride superconductor with a high Tc of approximately 235 K

High-Pressure Synthesis and Characterization of Cr-Doped Large Single-Crystal Diamonds

High-Pressure Synthesis and Characterization of Cr-Doped Large Single-Crystal Diamonds

High-Pressure Synthesis of Corundum-Type Ga2O3:Cr3+ and Application of Its Fluorescence to the Pressure Scale.

Cr3+-doped Ga2O3 crystals with a corundum structure were synthesized at high temperature and high pressure, and their excitation as well as fluorescence properties were evaluated. The crystals were green under white light illumination but deep red when exposed to ultraviolet light. This can mainly be attributed to R1 and R2 fluorescence spectra caused by the Cr3+ transition. The pressure-dependence of their fluorescence spectra is comparable with ruby (Al2O3:Cr3+), which is currently often used as a pressure scale. The excitation spectrum was shifted to the long-wavelength side compared with ruby, which enabled excitation with long-wavelength lasers, even if the pressure effect is considered. In addition, the R1 and R2 peaks were well-separated with increasing pressure, which might have advantages over the ruby scale.

High-pressure and high-temperature synthesis of crystalline Sb3 N5.

A chemical reaction between Sb and N2 was induced under high-pressure (32-35 GPa) and high-temperature (1600-2200 K) conditions, generated by a laser heated diamond anvil cell. The reaction product was identified by single crystal synchrotron X-ray diffraction at 35 GPa and room temperature as crystalline antimony nitride with Sb3 N5 stoichiometry and structure belonging to orthorhombic space group Cmc21 . Only Sb-N bonds are present in the covalent bonding framework, with two types of Sb atoms respectively forming SbN6 distorted octahedra and trigonal prisms and three types of N atoms forming NSb4 distorted tetrahedra and NSb3 trigonal pyramids. Taking into account two longer Sb-N distances, the SbN6 trigonal prisms can be depicted as SbN8 square antiprisms and the NSb3 trigonal pyramids as NSb4 distorted tetrahedra. The Sb3 N5 structure can be described as an ordered stacking in the bc plane of bi- layers of SbN6 octahedra alternated to monolayers of SbN6 trigonal prisms (SbN8 square antiprisms). The discovery of Sb3 N5 finally represents the long sought-after experimental evidence for Sb to form a crystalline nitride, providing new insights about fundamental aspects of pnictogens chemistry and opening new perspectives for the high-pressure chemistry of pnictogen nitrides and the synthesis of an entire class of new materials.

Xylitol: Production and its applications – A Review

Xylitol is important chemical due to its various applications. The use of xylitol as a sweetener for diabetic patients has made it a high valuable special chemical. As xylitol is present in low concentrations in fruits and vegetables, therefore its extraction is unaffordable from these sources. Thus, xylitol can be produced chemically by reduction of xylose in presence of suitable reducing agents and microbial route method. Although several species of yeast, fungi and bacteria synthesize xylitol by the species of the genus Candida, Saccharomyces, Pichia, Debaryomyces, Trichosporon, Enterobacter, Corynebacterium, Mycobacterium etc. The chemical synthesis of xylitol from xylose is the dominant production method of xylitol production. The industrial process to produce xylitol involves the chemical hydrolysis of D-xylose followed by the hydrogenation of the resultant hemicellulose hydrolysate by catalysts including palladium and nickel. For the chemical synthesis of xylitol, high temperatures and high pressure are required. These processes are very expensive which makes the production costs of synthesizing xylitol because of the highly energy intensive, high temperature, pressure and metal catalyst used for a sustained period of time. Therefore, in this review article we study the microbial route of xylitol production from agricultural residues.

Experimental and numerical investigation of high-pressure methane catalytic synthesis from H2 and CO2

The catalytic synthesis of methane from H2 and CO2, which is an efficient way for the production of synthetic natural gas (SNG) by utilizing the H2 originating from carbon-free renewable power sources and the greenhouse gas CO2, was investigated in a non-isothermal channel-flow reactor coated with Ni/Al2O3 at pressures 1.5–10 bar, H2:CO2 volumetric ratios 4–6, and surface temperatures 450–760 K. In situ, spatially resolved Raman measurements of gas-phase species concentrations across the channel height were complemented by gas chromatography analysis of the exhaust gas. Two-dimensional simulations were carried out, using elementary catalytic and gaseous chemical reaction mechanisms and detailed transport. Comparisons of the Raman data and simulations revealed that the preferential diffusion of H2 drastically altered the local H2:CO2 ratios at the catalytic walls, which attained values up to 8 times higher than the corresponding inlet values. This behavior exemplified the caution needed when performing kinetic studies in the mixed kinetically/transport controlled regime. The production of methane increased with increasing pressure and decreasing H2:CO2 ratio. At the highest ratio H2:CO2 = 6, the simulations underpredicted (overpredicted) the measured reactant (product) mole fractions, however, as H2:CO2 decreased, the trend was reversed. The discrepancies reduced with increasing pressure, resulting in a model overprediction of methane by 7.4% at 10 bar. Methane was produced from C(s) via successive hydrogenation. C(s) was in turn produced from COOH(s), followed by dissociation of COOH(s) to CO(s), and finally H-assisted dissociation of CO(s) to C(s). Gas-phase chemistry was negligible over the investigated conditions. The in-channel Raman measurements in conjunction with the exhaust gas analysis facilitated the construction of a global step for the studied reaction. The methane synthesis was assessed to follow a ∼p0.41 pressure dependence over the temperature range 520–680 K.

Centrosymmetric to non-centrosymmetric transition in the Ca2-xMnxTi2O6 double perovskite system studied through structural analysis and dielectric properties.

We have used high-pressure synthesis to synthesize samples of Ca2-xMnxTi2O6 double perovskite, where x varies between 0.2 and 1. The synthesized materials were structurally characterized with powder X-ray diffraction (XRD). Rietveld refinement of the XRD patterns was used to study the change from CaTiO3 (x = 0) to the composition CaMnTi2O6 (x = 1) where half of the Ca(II) ions are replaced by smaller Mn(II) ions. We analyzed the peak shapes in the XRD patterns, as well as lattice parameters, and it appears that smooth symmetry change from the centrosymmetric space group Pbnm to the non-centrosymmetric space group P42mc occurs between x = 0.3 and x = 0.5. We also confirmed the centrosymmetric to non-centrosymmetric transition by characterizing the dielectric properties of the materials with ferroelectric measurements.