High-pressure Synthesis Research Articles

Formation of the Metastable Iron (III) Germanate Fe2GeO5 through Kinetic Control of the Oxidative Reaction

Abstract Synthesis of complex oxides requires high temperatures to overcome barriers due to the diffusion of solids. Therefore, the most stable polymorphs are obtained in general reactions. However, it is necessary to design kinetic reactions with low initial energy barriers and control the reaction path and products to synthesize novel and metastable oxides. We report the synthesis of a metastable Fe2GeO5 with a kyanite-type structure via kinetic control of oxidative reaction in Fe2GeO4. It is also found that Fe2GeO5 was not synthesized at all by the conventional method, high-pressure synthesis method, or coprecipitation method. Our result indicates that kinetic control of the oxidative reaction is a promising method for synthesizing metastable materials.

High-Pressure Synthesis of 1D Low-Bandgap Polymers Embedded in Diamond-like Carbon Nanothreads

The synthesis of hydrogenated carbon nanothreads at tens of GPa from aromatic systems is one of the most brilliant recent findings in high-pressure science. C-nanothreads combine the high tensile strength of diamond with the high flexibility of polymers, and many efforts are currently being undertaken to taylor some useful physicochemical properties by smartly modifying their local structure. We present the synthesis of double core diamond-like nanothreads with the two cores being bound by a conjugated C, polyacetylene-like backbone. The two cores also form a protecting sheath for the backbone. This material exhibits an optical bandgap of 1.74 eV, similar to polyacetyelene; it is then very attractive as a potential organic semiconductor with simultaneous outstanding mechanical properties. The synthesis was achieved by reacting diphenylacetylene in diamond anvil cells, at 25–30 GPa and room temperature, and the materials were characterized by optical spectroscopy, synchrotron X-ray diffraction, and ab initio computer simulations.

High-Pressure Synthesis of Polar and Antiferromagnetic Mn2MnMoO6

High-Pressure Synthesis of Polar and Antiferromagnetic Mn₂MnMoO₆

High-Pressure Synthesis of Light Lanthanide Dodecaborides (PrB12 and CeB12): Effects of Valence Fluctuation on Volume and Formation Pressure.

Light lanthanide dodecaborides, RB12 (R = Pr and Ce), were synthesized from a stoichiometric mixture of hexaborides and boron using a laser-heated diamond anvil cell under high-pressure and high-temperature conditions. Contrary to the expectation that lighter lanthanide elements require higher pressure to crystallize RB12, in situ X-ray diffraction experiments reveal that cerium dodecaboride crystallizes at 26 GPa, which is significantly lower than that required to form the heavier praseodymium dodecaboride (35 GPa). In addition to the lower formation pressure, an anomalous volume reduction is also observed in CeB12, which can be explained by a valence fluctuation between Ce3+ and Ce4+ indicated by X-ray absorption near-edge structure measurements. A polyhedral coordination change from a truncated cube in RB6 to a truncated octahedron in RB12 and associated shortening of the R-B bond length result in an increase in bulk modulus and hardness.

Stability of hypothetical AgIICl2 polymorphs under high pressure, revisited: a computational study

A comparative computational study of stability of candidate structures for an as-yet unknown silver dichloride AgCl2 is presented. It is found that all considered candidates have a negative enthalpy of formation, but are unstable towards charge transfer and decomposition into silver(I) chloride and chlorine within the DFT and hybrid-DFT approaches in the entire studied pressure range. Within SCAN approach, several of the “true” AgIICl2 polymorphs (i.e. containing Ag(II) species) exhibit a region of stability below ca. 20 GPa. However, their stability with respect to aforementioned decomposition decreases with pressure by account of all three DFT methods, which suggests a limited possibility of high-pressure synthesis of AgCl2. Some common patterns in pressure-induced structural transitions observed in the studied systems also emerge, which further testify to an instability of hypothetical AgCl2 towards charge transfer and phase separation.

High-Pressure Synthesis of Transition-Metal Oxyhydrides with Double-Perovskite Structures.

We report on the high-pressure synthesis, crystal structure, and magnetic properties of four novel transition-metal oxyhydrides─Ba2NaVO3H3, Ba2NaVO2.4H3.6, Ba2NaCrO2.2H3.8, and Ba2NaTiO3H3─crystallizing in the double-perovskite structure. Notably, they have a higher hydride content in their anion sites (50%-63%) than known oxyhydrides with perovskite structures do (≤33%). Vanadium and chromium oxyhydrides exhibited Curie-Weiss magnetic susceptibilities with no magnetic ordering down to 2 K, which may be due to geometrical frustration in their face-centered lattices and weak magnetic interactions. Density functional theory calculations revealed that the transition metal-hydride bonding nature of the prepared oxyhydrides is more covalent than that observed for known perovskite oxyhydrides, as evidenced by the shorter bond lengths of the former. Remarkably, our double-perovskite oxyhydrides with a high hydride content may possess a bonding character intermediate between those of known oxyhydrides and hydrides.

Exploratory Synthesis for Complex Metal Fluorides Using Solid-State Fluorine Sources

We attempted to synthesize complex metal fluorides via reaction between metal and solid-state fluorine sources and succeeded in preparing trirutile-type Li2MoF6 using LiF, the metal Mo, and CuF2. We also found a new phase of Li2MoF6 that is isostructural with trigonal Li2ZrF6 via a combination of solid-state fluorine sources and high-pressure synthesis. The reaction occurs exothermically and involves conversion and addition associated with redox reaction, and CuF2 then functions as both an oxidizing agent and fluorine source. Because the overall reaction proceeds stoichiometrically, the required amount of fluorine can be controlled by the amount of solid-state fluorine agents. The synthesis route was also applicable for the preparation of other known fluorides, Li2MF6 (M = Ti, Zr, and Nb) and β-Li3MF6 (M = Ti and V). The synthetic route using a solid-state fluorine source is suitable for the exploration of novel inorganic complex metal fluorides.

Intrinsically low thermal conductivity of tetragonal-structured PbSe2

Designing new compounds with earth-abundant constituent elements and intrinsically low thermal conductivity are crucial to the development of thermoelectric materials. In this letter, the tetragonal-structured PbSe 2 with extremely low thermal conductivity was prepared by two-step ball milling and high pressure synthesis method. Density functional theory calculation shows that the low thermal conductivity of PbSe 2 is originated from its weak interatomic bonding strength and high lattice vibration anharmonicity. We also found that the carrier concentration of PbSe 2 can be tuned effectively by Ag doping in Pb site, which leads to an enhanced figure of merit. These results indicate that PbSe 2 is a potential candidate as a thermoelectric material. • Tetragonal structured PbSe 2 was synthesized by a high-pressure method. • PbSe 2 behaves an extremal low thermal conductivity. • The carrier concentration and ZT of PbSe 2 was enhanced effectively by Ag doping.

High pressure synthesis and the valence state of vanadium ions for the novel transition metal pernitride, CuAl2-type VN2.

A novel transition metal pernitride, CuAl2-type VN2, has been synthesized at a pressure above 73.3 GPa. The bulk modulus has been determined to be K0 = 347(12) GPa. By hard X-ray absorption spectrum measurements of VN2, the valence state of transition metal ions in pernitrides has been for the first time experimentally reported.

High-pressure synthesis, crystal structure, and physical properties of NaAlB14 single crystals

Pure NaAlB14 single crystals were successfully synthesized directly from Na, Al, and B at high pressure and high temperature, different from the previously reported method, that is, synthesized from Na2B4O7, Al, and B. The growth of NaAlB14 single crystals was promoted by increasing the reaction temperature. The atomic structures of NaAlB14 single crystal along the [100], [010], [001], and [021] axes were characterized by using a scanning transmission electron microscope. The Raman spectra of NaAlB14 were investigated theoretically and experimentally, and they showed the expected oscillations of the covalent framework. In addition, photoluminescence spectra indicated that NaAlB14 is a semiconductor luminescence material with red (1.68 eV) and near-infrared (1.50 and 1.36 eV) emission characteristics. The band structure revealed that NaAlB14 is an indirect band gap semiconductor with a wide band gap of 2.22 eV.

Sc1−xErxAlO3perovskites: high-pressure synthesis, photoluminescence properties, andin vitrobioimaging

In vitrobioimaging of HEK293 cells using the green luminescent Sc0.98Er0.02AlO3compound.

The non-centrosymmetric layered compounds IrTe2I and RhTe2I.

The previously unreported layered compounds IrTe2I and RhTe2I were prepared by a high-pressure synthesis method. Single crystal X-ray and powder X-ray diffraction studies find that the compounds are isostructural, crystallizing in a layered orthorhombic structure in the non-centrosymmetric, non-symmorphic space group Pca21 (#29). Characterization reveals diamagnetic, high resistivity, semiconducting behavior for both compounds, consistent with the +3 chemical valence and d6 electronic configurations for both iridium and rhodium and the Te-Te dimers seen in the structural study. Electronic band structures are calculated for both compounds, showing good agreement with the experimental results.

Phosphorous-Based Zintl Compounds as Viable Semimetals

A black-phosphorus-derived Zintl compound, MoP4, is obtained by high-pressure synthesis. The material exhibits a non-quadratic large magnetoresistance and semi-metallic Seebeck behavior, as predicted by the first principles calculations yielding massive and non-symmorphic Dirac semimetal states.

A New High Pressure and High Temperature Synthesis Idea Preparation of Micron Polycrystalline Transparent Cubic Boron Nitride

A New High Pressure and High Temperature Synthesis Idea Preparation of Micron Polycrystalline Transparent Cubic Boron Nitride

Probing the methanol-assisted autocatalytic formation of methanol over Cu/ZnO/Al2O3 by high-pressure methanol and methyl formate pulses

Using high-pressure methanol and methyl formate pulses as a surface-sensitive operando method for high-pressure methanol synthesis over Cu/ZnO/Al2O3, the recently found autocatalytic pathway was confirmed.

NaCo2(SeO3)2(OH): competing magnetic ground states of a new sawtooth structure with 3d7 Co2+ ions

We report the high-pressure synthesis and a comprehensive study of NaCo2(SeO3)2(OH) sawtooth chain structure using bulk magnetic properties and neutron scattering.

Characterization of the (Cu,C)Ba2Ca3Cu4O single crystals grown under high pressure

By using a high pressure and high temperature (3.7 GPa, 1120 ∘C) synthesis technique, we have grown (Cu,C)Ba2Ca3Cu4O single crystals. X-ray diffraction, scanning electron microscopy, resistivity, and magnetization measurements are carried out and all show that the samples have good quality. The single crystal has onset and zero-resistance transition temperatures of about 111 and 109.6 K, indicating a very narrow transition width, which is consistent with a rather sharp magnetization transition. Magnetization hysteresis loops (MHLs) are also measured, showing a pronounced second peak effect in the intermediate temperature region. The magnetic critical current density calculated from the MHLs at 77 K and 1.5 T is about 6.4 × 104 A cm−2. By using a criterion of 1 normal state resistivity, we have determined the irreversibility line which exhibits an irreversibility field of about 8 T at 77 K. Compared with other layered systems, it is easy to find that the irreversibility line is rather high and could be further improved with the optimized transition temperature of about 118 K as previously discovered in polycrystalline samples.

The effects of Cu-substitution and high-pressure synthesis on phase transitions in Ni2MnGa Heusler alloys

The magnetic, structural, and thermal behaviors of the Cu-doped Heusler alloy Ni2Mn1−xCuxGa (0 ⩽ x ⩽ 0.4) were studied as a function of concentration x. As the Cu concentration increased, the structural transition temperatures increased, whereas the chemical order-disorder transitions and melting points decreased. The experimental results from temperature dependent X-ray diffraction reveal different crystal structures of the martensite phase at low temperatures for samples with different x, but all the samples ultimately crystallized in the L21 cubic crystal structure upon heating above their respective structural transitions. The experimental data were used to construct a comprehensive magnetic and structural phase diagram as a function of x from below their respective structural transition temperatures to their melting temperatures. The XRD analysis shows that the observed volume reduction is associated with the increasing structural transition temperature. Therefore, one of the samples was annealed under high pressure to permanently reduce its volume, and the correlation between the increasing structural transition temperatures and volumes was confirmed.

Methodological Approach to the High-Pressure Synthesis of Nonmagnetic Li2B4+B′6+O6 Oxides

High-pressure solid-state synthesis advances boost discoveries of new materials and unusual phenomena but endures stringent recipe conditions, poor yield, and high cost. A methodological approach for accelerated and precisely high-pressure synthesis is therefore highly desired. Here, we take the exotic double-perovskite-related nonmagnetic Li2B+4B′+6O6 as an example to show the pipeline of data-mining, high-throughput calculations, experimental realization, and chemical interception of metastable phases. A total of 140 compounds in 7 polymorph categories were initially screened by the convex hull, which left ∼50% candidates in chemical space on the phase diagram of pressure-dependent polymorph evolution. Li2TiWO6 and Li2TiTeO6 were singled out for experimental testing according to the predicted map of crystal structure, function, and synthesis parameters. Computation on surface energy effect and interfacial chemical strain suggested that the as-made high-pressure R3-Li2TiTeO6 polymorph cannot be intercepted below a critical nanoscale but can be stabilized in heterojunction film on a selected compressive substrate at ambient pressure. The developed methodology is expected to accelerate the big-data-driven discovery of generic chemical formula-based new materials beyond perovskites by high-pressure synthesis and shed light on the large-scale stabilization of metastable phases under mild conditions.

Superconductivity in In-doped AgSnBiTe3 with possible band inversion

We investigated the chemical pressure effects on structural and electronic properties of SnTe-based material using partial substitution of Sn by Ag0.5Bi0.5, which results in lattice shrinkage. For Sn1−2x(AgBi)xTe, single-phase polycrystalline samples were obtained with a wide range of x. On the basis of band calculations, we confirmed that the Sn1−2x(AgBi)xTe system is basically possessing band inversion and topologically preserved electronic states. To explore new superconducting phases related to the topological electronic states, we investigated the In-doping effects on structural and superconducting properties for x = 0.33 (AgSnBiTe3). For (AgSnBi)(1−y)/3InyTe, single-phase polycrystalline samples were obtained for y = 0–0.5 by high-pressure synthesis. Superconductivity was observed for y = 0.2–0.5. For y = 0.4, the transition temperature estimated from zero-resistivity state was 2.4 K, and the specific heat investigation confirmed the emergence of bulk superconductivity. Because the presence of band inversion was theoretically predicted, and the parameters obtained from specific heat analyses were comparable to In-doped SnTe, we expect that the (AgSnBi)(1−y)/3InyTe and other (Ag, In, Sn, Bi)Te phases are candidate systems for studying topological superconductivity.