High-pressure Synthesis Method Research Articles

Discovery of Rhombohedral NaIrO3 Polymorph by In Situ High-Pressure Synthesis of High-Oxidation-State Materials Using Laser Heating in Diamond Anvil Cells.

We report a new in situ synthesis method effective for discovery of high-oxidation-state materials using laser-heated diamond anvil cells. The issue of chemical reduction during thermally induced phase transitions that occur spontaneously in a noble gas pressure transmitting media (PTM) can be overcome by thermal decomposition of an oxygen-rich solid PTM (NaCl + NaClO3). To illustrate the technical challenges the method overcomes, we applied this new method for two known pentavalent A(I)B(V)O3 postperovskite compounds. We successfully synthesized the two postperovskites, NaOsO3 and NaIrO3, and quenched to ambient conditions. Furthermore, we report the discovery of a new low-pressure polymorph of NaIrO3, illustrating the high potential for new materials discovery. This new method will enable realization of new high-oxidation-state postperovskites and can be applied for many other structure families in a P, T parameter space that is not easily accessible using conventional high-pressure synthesis methods.

Thermoelectric performance of p-type CaxFe1.3Co2.7Sb12 skutterudites from high pressure synthesis

P-type CaxFe1.3Co2.7Sb12 skutterudites were successfully synthesized with a high pressure synthesis method followed by spark plasma sintering. The structure, composition and thermoelectric properties were investigated. With fixed Fe substitution level, the hole concentration was tuned with Ca filling. Compared with the unfilled Co3.25Fe0.73Sb12, Ca-filled samples possessed a relatively large effective mass, which is beneficial for enhancements in Seebeck coefficient and power factor. Moreover, the joint impurity and rattling mode scattering further suppressed the lattice thermal conductivity. Consequently, the Ca0.6Fe1.3Co2.7Sb12 sample showed the optimal ZT of 0.70 at 820 K. Composition analysis and simple electron counting suggested 0.77 hole per molecular formula for this sample, close to the value (about 0.7) we proposed for optimal filling and substitution contents in Co-rich p-type skutterudites.

High-pressure Synthesis of Ba2CoO2Ag2Te2 with Extended CoO2 Planes

Using a high-pressure synthesis method, we prepared the layered oxychalcogenide Ba2CoO2Ag2Te2 (space group: I4/mmm) with alternating stacks of CoO2 and Ag2Te2 layers, separated by Ba atoms. The CoO2 plane is greatly extended (Co-O = 2.19 Å on average) due to tensile strain from adjacent Ag2Te2 layers, causing displacement of oxide anions. Layered cobaltates with trans-CoO4X2 (X = chalcogen, halogen) coordination feature large spin-orbit coupling, which is linearly scaled by the tetrahedral factor of dCo-X/dCo-O. However, applying this relation to Ba2CoO2Ag2Te2 yields a magnetic moment of ∼4 μB, which is nearly twice the experimentally observed value of 1.87(17) μB. This result, along with a reduced Néel temperature (TN = 60 K), originates from the off-centered position of otherwise under-bonded oxide anions, which changes the crystal field splitting of Co d orbitals.

Synthesis and performance of TiB2–B4C composites by high pressure of TiC–B mixture

AbstractTiB2–B4C composites were in situ synthesized and consolidated by high pressure synthesis method from a mixture of TiC and B powders at the pressure and temperature of 5.0 GPa and 1500℃‐1900℃. The phase composition, microstructure, density, hardness, thermal conductivity, and electrical resistivity of TiB2–B4C composites were analyzed. As the increase in the synthesis temperature, the products were TiB2 and B4C phases and that crystallinity improved. TiB2–B4C composites were dense without obvious pores. TiB2–B4C composites synthesized at 1800℃ obtained the optimized performance, including the relative density of 98.2%, the Vickers hardness of 31.7 ± 1.2 GPa with the load of 9.8 N, the thermal conductivity of 30.3 ± 0.7 W/(m K), and the electrical resistivity of 3.3 × 10−3 Ω cm, respectively. The grain size of the TiB2–B4C composites changed with the increase in synthesis temperature, leading to the changes in hardness, thermal conductivity, and electrical resistivity.

Experimental Study on Preparation of Ferropericlase by Oxalate Coprecipitation

It is always a goal of scientists to develop new techniques to identify the composition of mantle materials and understand geodynamic processes accurately. Ferropericlase (Mg,Fe)O is a prominent mineral in the lower mantel. It is a common practice in the research community to prepare ferropericlase using a solid-phase synthesis method or high-pressure experiment synthesis method. This conventional method contains a number of ambiguities a great deal of time is needed. In this paper, we have addressed the drawbacks of the conventional technique using a liquid-phase synthesis method to prepare ferropericlase. During the experiment, oxalic acid was added to a mixed solution of ferrous sulfate and magnesium chloride and mixed according to the molar ratio. The formed magnesium iron oxalate precipitate was sintered and reduced into the final sample. Furthermore, the final sample was analyzed using XRD and SEM. Compared to the solid-phase method, this coprecipitation method could produce ferropericlase with a shorter sintering time, lower sintering temperature, and a reduction in the amount of gas consumed. XRD and SEM results show that the liquid-phase method produced samples with better composition homogeneity.

Near-Room-Temperature Ferrimagnetic Ordering in a B-Site-Disordered 3d-5d-Hybridized Quadruple Perovskite Oxide, CaCu3Mn2Os2O12.

A new 3d-5d hybridization oxide, CaCu3Mn2Os2O12 (CCMOO), was prepared by high-pressure and high-temperature synthesis methods. The compound crystallizes to an A-site-ordered but B-site-disordered quadruple perovskite structure with a space group of Im3̅ (No. 204). The charge states of the transition metals are determined to be Cu2+/Mn3.5+/Os4.5+ by X-ray absorption spectroscopy. Although most B-site-disordered perovskites possess lower spin-ordering temperatures or even nonmagnetic transitions, the current CCMOO displays a long-range ferrimagnetic phase transition with a critical temperature as high as ∼280 K. Moreover, a large saturated magnetic moment is found to occur [7.8 μB/formula units (f.u.) at 2 K]. X-ray magnetic circular dichroism shows a Cu2+(↑)Mn3.5+(↑)Os4.5+(↓) ferrimagnetic coupling. The corner-sharing Mn/OsO6 octahedra with mixed Mn and Os charge states make the compound metallic in electrical transport, in agreement with a specific heat fitting at low temperature. This work provides a rare example with high spin-ordering temperature and a large magnetic moment in B-site-disordered 3d-5d hybridization perovskite oxides.

Tailoring band structure and band filling in a simple cubic (IV, III)-VI superconductor

Superconductivity and its underlying mechanisms are one of the most active research fields in condensed-matter physics. An important question is how to enhance the transition temperature $T_{\rm c}$ of a superconductor. In this respect, the possibly positive role of valence-skipping elements in the pairing mechanism has been attracting considerable interest. Here we follow this pathway and successfully enhance $T_{\rm c}$ up to almost 6 K in the simple chalcogenide SnTe known as topological crystalline insulator by doping the valence-skipping element In and codoping Se. A high-pressure synthesis method enabled us to form single-phase solid solutions Sn$_{1-x}$In$_{x}$Te$_{1-y}$Se$_{y}$ over a wide composition range while keeping the cubic structure necessary for the superconductivity. Our experimental results are supported by density-functional theory calculations which suggest that even higher $T_{\rm c}$ values would be possible if the required doping range were experimentally accessible.

High-pressure-assisted design of porous topological semimetal carbon for Li-ion battery anode with high-rate performance

It has been a great challenge to develop a high-rate anode material with high-capacity, fast Li-ions diffusion and long cycling life going beyond the commercially used graphite in Li-ion battery. Here for the first time we propose a strategy combined high-pressure synthesis method with the global structure search to find a topological semimetal porous carbon as the desired anode. Our crystal-structure searching shows that we can obtain the ground state of an orthorhombic phase $\mathrm{Li}{\mathrm{C}}_{6}$ with regular pores at 30 GPa, and when the Li atoms are removed, the resulting carbon structure is the recently predicted interlocked graphene network (IGN) that is a topological semimetal with an intrinsic high electronic conductivity. Based on the state-of-the-art first-principles calculations, we further find that the Li-ion migration energy barrier in the IGN is extremely low and the estimated diffusion coefficient can reach a magnitude of ${10}^{\ensuremath{-}4}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}/\mathrm{s}$ at both low and high Li concentrations, which is three orders of magnitude larger than that of graphite anode. Moreover, the volume changes during the Li insertion and deinsertion are smaller than $3.2%$, while the theoretical specific capacity is the same as that of graphite anode. Our studies not only suggest a practical way of synthesizing the topological semimetal carbon but also propose a new anode material for Li-ion battery.

Magnetization of potassium-doped p -terphenyl and p -quaterphenyl by high-pressure synthesis

By using high pressure synthesis method, we have fabricated the potassium doped para-terphenyl. The temperature dependence of magnetization measured in both zero-field-cooled and field-cooled processes shows step like transitions at about 125 K. This confirms earlier report about the possible superconductivity like transition in the same system. However, the magnetization hysteresis loop exhibits a weak ferromagnetic background. After removing this ferromagnetic background, a Meissner effect like magnetic shielding can be found. A simple estimate on the diamagnetization of this step tells that the diamagnetic volume is only about 0.0427% at low temperatures, if we assume the penetration depth is much smaller than the size of possible superconducting grains. This magnetization transition does not shift with magnetic field but is suppressed and becomes almost invisible above 1.0 T. The resistivity measurements are failed because of an extremely large resistance. By using the same method, we also fabricated the potassium doped para-quaterphenyl. A similar step like transition at about 125 K was also observed by magnetization measurement. Since there is an unknown positive background and the diamagnetic volume is too small, it is insufficient to conclude that this step is derived from superconductivity although it looks like.

Highly oriented epitaxial CaFe2O4 thin films on TiO2 substrates grown by pulsed-laser deposition

CaFe2O4 (CFO) is an oxide semiconductor being usable for a photocathode, but its single crystal is so far grown only by a high-pressure bulk synthesis method. Using pulsed-laser deposition, we have obtained the (010)-oriented CFO films on TiO2 (100) substrates. The epitaxial structure included twin domains with 1.5° tilting from the surface normal and sixfold domains with in-plane rotations of ±70° with respect to the b axis of TiO2, which was explained by taking a number of probable arrangements between FeO6 and TiO6 octahedra into account. X-ray absorption spectroscopy and ultra-violet-visible-near-infrared spectroscopy measurements revealed the electronic properties similar to those of bulk and thus the CFO films would be suitable to the investigation of photocathodic performance.

High-pressure synthesis and thermoelectric performance of tellurium doped with bismuth

Recently, it was found that element semiconductor tellurium (Te) has a high thermoelectric performance. However, it needs to be doped with high-toxic arsenic (As) to tune the carrier concentration of Te. In this paper, low-toxic bismuth (Bi) was employed as dopant to optimize the thermoelectric performance of Te combining with a high-pressure synthesis method. The effect of substituting Bi on the electrical transport and thermal transport properties of Te has been investigated. The results show that the solubility limit of Bi in Te is about 0.1 mol%. However, the trace amounts of Bi doping can tune the carrier concentration of Te effectively and thereby optimize its power factor. The thermal conductivity of non-doped Te prepared by high pressure is much lower than that of the sample prepared at ambient pressure. And Bi doping can further decrease the value due to the phonons scattered by the heavy impurity atom. An enhanced figure of merit ZT ~ 0.72 was obtained at 517 K, which is about four times that of non-doped Te and is comparable to the state-of-the-art thermoelectric alloys with more complex composition such as Bi2Te3 and PbTe.

High pressure synthesis and thermoelectric properties of Ba-filled CoSb3 skutterudites

The filling behavior of barium into voids of CoSb3 under high pressure was investigated with the first principles calculations, revealing that the filling fraction limit can be further increased under high pressure. Inspired by the theoretical investigation result, we synthesized Ba-filled CoSb3 with a high pressure synthesis method. The products show the skutterudite structure of \(\operatorname{Im}\bar{3}\) symmetry. The maximal filling fraction of Ba in CoSb3 is increased to 0.51. The power factor is significantly enhanced meanwhile the lattice thermal conductivity is dramatically suppressed after Ba filling, and ZT of Ba0.51Co4Sb12 reaches a value of ca. 1.0 at 883 K. Compared with the traditional solid state reaction method for fabricating elemental-filled skutterudites, the high pressure synthesis method shows the advantages of fast process, broadening fillable elements, and increasing the filling fraction.

Thermoelectric properties of high pressure synthesized lithium and calcium double-filled CoSb3

Lithium and calcium are inefficient filling elements of CoSb3 at ambient pressure, but show nice filling behavior under high pressure. In this work, we synthesized Li/Ca double-filled CoSb3 with high pressure synthesis method. The products show the skutterudite structure of Im3¯ symmetry. Thermoelectric properties were effectively enhanced through Li and Ca co-filling. For the optimal Li0.08Ca0.18Co4Sb12 sample, the power factor maintains a relatively high value over the whole measurement temperature range and peaks at 4700μWm−1K−2, meanwhile the lattice thermal conductivity is greatly suppressed, leading to a maximal ZT of 1.18 at 700 K. Current work demonstrates high pressure synthesis as an effective method to produce multiple elemental filled CoSb3 skutterudites.

Scintillation properties of high-pressure-synthesized ZnO ceramics

We synthesized ZnO ceramics scintillators without or with dopants using a high-pressure synthesis method. The dense ceramics were successfully obtained, and the densified structure was confirmed by SEM observation. Doping with Ga is proven to be effective for suppressing the deep level (DL) emission as well as the long decay component in the scintillation temporal profile. Based on the pulse height spectra, the light yield is estimated to be 1500 photons/5.5-MeV alpha-ray for the undoped ceramics, and the doped ceramics exhibit similar light yields. These results indicate that the high-pressure synthesis method is effective for the synthesis of dense ZnO ceramics scintillators with a fast response.

LaMn3Ni2Mn2O12: An A- and B-Site Ordered Quadruple Perovskite with A-Site Tuning Orthogonal Spin Ordering

A new oxide, LaMn3Ni2Mn2O12, was prepared by high-pressure and high-temperature synthesis methods. The compound crystallizes in an AA′3B2B′2O12-type A-site and B-site ordered quadruple perovskite structure. The charge combination is confirmed to be LaMn3+3Ni2+2Mn4+2O12, where La and Mn3+ are 1:3 ordered at the A and A′ sites and the Ni2+ and Mn4+ are also distributed at the B and B′ sites in an orderly fashion in a rocksalt-type manner, respectively. A G-type antiferromagnetic ordering originating from the A′-site Mn3+ sublattice is found to occur at TN ≈ 46 K. Subsequently, the spin coupling between the B-site Ni2+ and B′-site Mn4+ sublattices leads to an orthogonally ordered spin alignment with a net ferromagnetic component near TC ≈ 34 K. First-principles calculations demonstrate that the A′-site Mn3+ spins play a crucial role in determining the spin structure of the B and B′ sites. This LaMn3Ni2Mn2O12 provides a rare example that shows orthogonal spin ordering in the B and B′ sites assisted by ordered A-site magnetic ions in perovskite systems.

High-Pressure Synthesis of Skutterudite-Type Thermoelectric Materials

We have developed a manufacturing system by combination of high-pressure synthesis method using a multi-anvil press, and spark plasma sintering (SPS) method. By means of the system, we have succeeded in synthesizing new filled skutterudite-type thermoelectric materials MmxCo4Sb12 (Mm=mischmetal). The thermoelectric properties of partially filled skutterudite compounds MmxCo4Sb12 synthesized under high pressure have been investigated. The Seebeck coefficient of MmxCo4Sb12 shows negative value, which means n-type conductivity. The highest dimensionless figure of merit ZT value is 0.25 for Mm0.6Co4Sb12 at 700 K.

High-Pressure Synthesis and Superconductivity of Ag-Doped Topological Crystalline Insulator SnTe (Sn1−xAgxTe with x = 0–0.5)

We have synthesized the single-phase polycrystalline samples of Sn1-xAgxTe, Ag-doped topological crystalline insulator SnTe, with a range of x = 0-0.5 using a high-pressure synthesis method. The crystal structure of Sn1-xAgxTe at room temperature is a cubic NaCl-type structure, which does not vary upon Ag substitution. Bulk superconductivity with a transition temperature of 2.4 K was observed for x = 0.15-0.25, and the optimal Ag content was x = 0.2. The Sn1-xAgxTe superconducting phase will be useful for understanding the superconductivity nature and mechanisms of the carrier-doped SnTe system.

High Pressure Synthesis of p-Type CeyFe4-xCoxSb12 Skutterudites.

Co-substituted p-Type CeFe4−xCoxSb12 skutterudites were successfully synthesized with a high pressure synthesis method. The structure, composition, and thermoelectric properties were investigated. The obtained CeyFe4−xCoxSb12 samples show the skutterudite structure of symmetry. The hole concentration decreases with elevating Co substitution level, leading to increased Seebeck coefficient and electrical resistivity. Meanwhile, the filling fraction of Ce decreases, which is unfavorable for reducing the lattice thermal conductivity. As a result, the thermoelectric performance of CeyFe4−xCoxSb12 deteriorates with higher Co content. The maximal ZT of 0.91 was achieved at 763 K for the optimal Ce0.92Fe4Sb12 sample.

High pressure synthesis of p-type Fe-substituted CoSb3 skutterudites

Fe-substituted CoSb3 skutterudites were successfully synthesized with high pressure synthesis method. The composition, structure, and thermoelectric properties were investigated. Co4−xFexSb12 samples have the skutterudite structure of \(\text{Im} \bar{3}\) symmetry. The hole concentration increases with elevating Fe substitution level. Compared with those ambient-pressure synthesized Fe-substituted CoSb3 samples, our samples exhibit enhanced power factor and suppressed thermal conductivity which benefitted from high pressure. The optimal Co3.2Fe0.8Sb12 shows a peak ZT of 0.53 at 823 K, the highest value for Co-rich p-type skutterudites with single-element substitution. Current study on Co4−xFexSb12 provides a basis for further thermoelectric performance enhancement of Co-rich p-type skutterudites.

Soft chemical synthesis and electrochemical properties of calcium ferrite-type LixMn2O4

Calcium ferrite (CaFe2O4)-type LixMn2O4 was prepared via high-pressure and soft chemical synthesis method. The framework structure of CaFe2O4-type NaMn2O4 was synthesized from the stoichiometric mixture of Na2CO3 and MnO2 annealed by 1273 K for 1 h under 4.5 GPa. Na/Li ion-exchange of the CaFe2O4-type NaMn2O4 was carried out by soaking molten LiNO3 at 633 K for 12 h.The electrochemical properties of the ion-exchanged CaFe2O4-type LixMn2O4 were measured. The initial discharge profile in the voltage range from 4.0 to 1.0 V showed 458 mAh g−1 of the discharge capacity with two plateaus near 3.7 V and 2.7 V (vs. Li/Li+). The discharge capacity was decreased with increasing the cycle number. After 30 cycles, the capacity was decreased to 375 mAh g−1. When the range was set between 4.8 and 3.0 V, the discharge capacity was 113 mAh g−1 in initial, and 111 mAh g−1 after 50th cycle.The reference CaFe2O4-type LiMn2O4 was prepared via one-step high-pressure synthesis and compared the electrochemical properties with the ion-exchanged sample. The initial discharge capacity of the one-step synthesized one was 108 mAh g−1 at 1.0 V (vs. Li/Li+), which was 73% lower than the value of the ion-exchanged one.