High-pressure Form Research Articles

In situ observation of a first-order liquid–liquid transition in phosphorus

Recently, we have found an abrupt, pressure-induced structural change between two distinct forms of liquid phosphorus at about 1 GPa by an in situ X-ray diffraction method. X-ray diffraction of liquid phosphorus was measured up to 4.6 GPa and that of red amorphous phosphorus was measured at atmospheric pressure and 3.0 GPa. A model liquid of uncorrelated P 4 molecules roughly reproduces the structure factor of the low-pressure form. On the other hand, there are similarities in the structure factors of the high-pressure form, red phosphorus and liquid arsenic, indicating that the high-pressure form has a polymeric nature.

Structural transformations in cubic ZrMo 2O 8 at high pressures and high temperatures

High-pressure high-temperature syntheses using the γ-ZrMo 2O 8 (Pa 3 ̄ , Z=4) starting material with the structure of the β-ZrW 2O 8 type are carried out in a multi-anvil apparatus. The recovered products are examined with powder x-ray diffraction at ambient conditions. The sample obtained at 1.3 GPa and 298 K is partially amorphous and contains γ-ZrMo 2O 8. Up to the onset of amorphization at 1.3 GPa, the recovered products from near room and high temperatures are α-ZrMo 2O 8 (P 3 ̄ 1 c, Z=6) and β-ZrMo 2O 8 (C2/c, Z=4), respectively. In the structure of α-ZrMo 2O 8, layers of ZrO 6 octahedra and MoO 4 tetrahedra are joined together by van der Waals forces. β-ZrMo 2O 8 is built of infinite ribbons of edge-sharing ZrO 8 polyhedra joined by MoO 5 pyramids. The crystalline compounds synthesized at pressures above 1.3 GPa and at high temperatures originate from the pressure-induced amorphous phase of γ-ZrMo 2O 8. The higher the pressure during the synthesis the higher the temperature necessary to obtain a recoverable crystalline product. Up to about 4 GPa, the synthesized material is β-ZrMo 2O 8. The recovered crystalline phases from above 4.0 GPa are the ZrO 2MoO 3 decomposition products. One of them is the high-pressure high-temperature form of MoO 3 (P2 1/m, Z=2), with all the Mo atoms in the octahedral coordination.

Iron(III) Oxides from Thermal ProcessesSynthesis, Structural and Magnetic Properties, Mössbauer Spectroscopy Characterization, and Applications

Structural and magnetic properties, methods of synthesis, and applications of seven iron(III) oxide polymorphs, including rare beta, epsilon, amorphous, and high-pressure forms, are reviewed. Thermal transformations resulting in the formation of iron oxides are classified according to different parameters, and their mechanisms are discussed. 57Fe Mossbauer spectroscopy is presented as a powerful tool for the identification, distinction, and characterization of individual polymorphs. The advantages of Mossbauer spectroscopy are demonstrated with two examples related to the study of the thermally induced solid-state reactions of Fe2(SO4)3.

The Electrochemistry of Zn3 N 2 and LiZnN : A Lithium Reaction Mechanism for Metal Nitride Electrodes

LiZnN has been isolated by way of an electrochemical conversion reaction of with Li. We show that reversibly reacts with lithium electrochemically, exhibiting a large reduction capacity of 1325 mAh/g corresponding to the insertion of 3.7 Li per Zn. Of this initial capacity, 555 mAh/g were found to be reversible. Through the use of extensive in situ and ex situ X-ray diffraction, the reaction mechanism with lithium was identified as a conversion reaction of into LiZn and a matrix of the high pressure form of Upon oxidation, LiZn transformed into metallic Zn, while contributed to the transformation into LiZnN. This is the first identification of a reversible conversion mechanism. The formation of LiZnN as the new end member of the electrochemical reaction with lithium was identified as the cause of the irreversible loss observed during the first cycle. The and LiZn oxidation into LiZnN was found to be reversible upon subsequent cycles. Poor cycle life was mainly attributed to the electromechanical grinding of the Li-Zn alloying reaction. is also introduced as a material utilizing a similar conversion reaction but exhibiting improved cycle life. © 2002 Telcordia Technologies. All rights reserved.

Theoretical Prediction of Post‐Spinel Phases of Silicon Nitride

New phases of Si3N4 that may be stable at higher pressure than spinel have been searched using a first‐principles plane‐wave pseudopotential method. The CaTi2O4‐type phase is found to be the prime candidate for the post‐spinel phase among six phases selected on the analogy to high‐pressure oxides. The phase transformation from the spinel is predicted to occur at 210 GPa. All silicon atoms of the new phase are coordinated by six anions, similar to the case of the high‐pressure forms of SiO2 and SiC. Because of its high energy at zero pressure, this new phase may be difficult to quench. The bandgap increases with an increase of pressure when compared in the same polymorph. However, the bandgap and the net charge decrease in the order of β, spinel, and CaTi2O4‐type phases at zero pressure. The theoretical bulk modulus of the CaTi2O4‐type phase is comparable with that of spinel.

Phase diagram and equations of state of BaSO4

The phase diagram and equations of state of BaSO4, were determined up to 29 GPa and 1000 K in a resistance-heating type diamond anvil cell. At room temperature, barite is the stable form of BaSO4 which undergoes a reversible phase transition at 10 GPa. The high-pressure form is tentatively determined to be triclinic. At high temperature, a similar phase transition takes place in BaSO4, but at a pressure higher than that at room temperature. Our results indicate that the phase boundary of the two polymorphs in BasO4 has a positive slope (dT/dP) of 90 K/GPa. The equations of state for both barite and its high-pressure phase are reported.

Pressure-induced phase transitions in lanthanide monoantimonides with a NaCl-type structure

By use of synchrotron radiation the powder x-ray diffraction of LnSb $(\mathrm{L}\mathrm{n}=\mathrm{l}\mathrm{a}\mathrm{n}\mathrm{t}\mathrm{h}\mathrm{a}\mathrm{n}\mathrm{i}\mathrm{d}\mathrm{e})$ with a NaCl-type structure has systematically been studied up to 40 GPa at room temperature. First-order phase transitions with the crystallographic change occur for LnSb at high pressures. The structure of the high-pressure phases of LnSb is classified into three groups. The lighter LnSb $(\mathrm{L}\mathrm{n}=\mathrm{L}\mathrm{a},$ Ce, Pr, and Nd) have the tetragonal structure (distorted CsCl-type) at high pressures. The high-pressure form of the middle LnSb $(\mathrm{L}\mathrm{n}=\mathrm{S}\mathrm{m},$ Gd, and Tb) is unknown. The heavier LnSb $(\mathrm{L}\mathrm{n}=\mathrm{D}\mathrm{y},$ Ho, Er, Tm, and Lu) show the typical NaCl-CsCl $(B1\ensuremath{-}B2)$ transition at high pressures though the same transition is not observed in the heavier LnP and LnAs. The transition pressures of LnSb increase with decreasing lattice constant in the NaCl-type structure and do not depend on the structure of their high-pressure phases. The high-pressure structural behavior of LnSb is discussed.

On equilibria of finite pressure plasma in magnetic multipoles

Separable solutions of finite plasma pressure equilibrium in a point multipole are found. Using the energy principle it is demonstrated that these solutions are interchange stable for quadripole and sextipole configurations. The low and high pressure forms of the solution in sextipole configuration are explicitly displayed.

Influence of the Structure on the Electrochemical Performance of Lithium Transition Metal Phosphates as Cathodic Materials in Rechargeable Lithium Batteries: A New High-Pressure Form of LiMPO4 (M = Fe and Ni).

Influence of the Structure on the Electrochemical Performance of Lithium Transition Metal Phosphates as Cathodic Materials in Rechargeable Lithium Batteries: A New High-Pressure Form of LiMPO₄ (M = Fe and Ni).

Alpha-Na6Pb3(PS4)4, a noncentrosymmetric thiophosphate with the novel, saucer-shaped [Pb3(PS4)4]6- cluster, and its metastable, 3-dimensionally polymerized allotrope beta-Na6Pb3(PS4)4.

Discovered in a molten polythiophosphate salt reaction, the compound α-Na6Pb3(PS4)4 is a salt containing the molecular cluster [Pb3(PS4)4].6- The C3v symmetry and the saucer shape of this cluster enable columnar stacking along the c-axis. Interestingly, fast cooling of a melt of the stoichiometric composition “Na6Pb3(PS4)4” results in the putative high-pressure form β-Na6Pb3(PS4)4 in which the molecular clusters have essentially polymerized through intercluster Pb−S bonding. β-Na6Pb3(PS4)4 converts slowly (depolymerizes) to the α-form upon annealing below the melting point.

Influence of the Structure on the Electrochemical Performance of Lithium Transition Metal Phosphates as Cathodic Materials in Rechargeable Lithium Batteries: A New High-Pressure Form of LiMPO4 (M = Fe and Ni)

Materials built from MO6 octahedra linked to XO4 tetrahedra are good candidates for studying the different factors that determine the electrode potential. Among them, olivine-like LiMPO4 (M = trans...

Crystal structure and bonding in the high-pressure form of fluorite (CaF 2)

Single crystals of CaF 2 in the PbCl 2 structure were grown at high pressure in a molten calcium hydroxide flux, and the structure was refined by single crystal X-ray diffraction ( Pnma, a=6.018(2) Å, b=3.614(1) Å, c=7.023(2) Å). Calcium is in nine-coordination in this structure, with Ca–F distances range from 2.317 to 2.774 Å. The two distinct fluorine atoms are in four and five coordination with calcium. Both the ambient pressure fluorite phase and the high pressure phase of CaF 2 have calcium in a close-packed configuration, cubic in fluorite and hexagonal in the PbCl 2 phase. This allows a simple comparison of the Ca arrays between the two phases. It is found that the close-packed array in the PbCl 2 phase is contracted along a and b by 4.7 and 6.6%, respectively, and elongated along c by 4.8%, relative to the close-packed array in fluorite.

Reaction and Formation of Crystalline Silicon Oxynitride in Si–O–N Systems under Solid High Pressure

Oxidized amorphous Si3N4 and SiO2 powders were pressed alone or as a mixture under high pressure (1.0–5.0 GPa) at high temperatures (800–1700°C). Formation of crystalline silicon oxynitride (Si2ON2) was observed from amorphous silicon nitride (Si3N4) powders containing 5.8 wt% oxygen at 1.0 GPa and 1400°C. The Si2ON2 coexisted with β‐Si3N4 with a weight fraction of 40 wt%, suggesting that all oxygen in the powders participated in the reaction to form Si2ON2. Pressing a mixture of amorphous Si3N4 of lower oxygen (1.5 wt%) and SiO2 under 1.0–5.0 GPa between 1000° and 1350°C did not give Si2ON2 phase, but yielded a mixture of α,β‐Si3N4, quartz, and coesite (a high‐pressure form of SiO2). The formation of Si2ON2 from oxidized amorphous Si3N4 seemed to be assisted by formation of a Si–O–N melt in the system that was enhanced under the high pressure.

Enthalpy of formation of CaSi 2 O 5, a quenched high-pressure phase with pentacoordinate silicon

The monoclinic titanite-like high-pressure form of calcium disilicate has been synthesized and quenched to ambient conditions to form the triclinic low-pressure phase containing silicon in four-, five- and sixfold coordination. The enthalpy of formation of the quench product has been measured by high-temperature oxide melt calorimetry. The value obtained from samples from a series of several synthesis experiments is ΔH f = (−26.32 ± 4.27) kJ mol−1 for the formation from the component oxides, or ΔH f = (−2482.81 ± 4.59) kJ mol−1 for the formation from the elements. The result is identical within experimental error to available estimates, although the previously predicted energy difference between the monoclinic and triclinic phases could not be verified.

Structural study of GeS 2 glasses permanently densified under high pressures up to 9 GPa

The structures of GeS 2 glasses permanently densified under 1.5, 3.0, 4.5, 6.0 and 9.0 GPa have been investigated by means of Ge–K EXAFS, Ge–K and S–K XANES, X-ray radial distribution, Raman scattering and optical absorption. The experimental results have been analyzed based on the structures of α (high-temperature form)-, β (low-temperature form)- and II (high-pressure form)-GeS 2 crystals. The densities of permanently densified glasses increased monotonously with increasing applied-pressure until 6.0 GPa and then reached a constant value in a pressure range from 6.0 to 9.0 GPa. With increasing densification the structure of GeS 2 glass, which is an intermediate between the structures of α-GeS 2 and β-GeS 2 at atmospheric pressure, was progressively converted into a II-GeS 2-like structure with no large hollows. The red shift of optical absorption edge in the visible region that results from densification exhibited the same pressure dependence as that observed for density.

ＮａＣｌ型構造を持つＬｎＸ（Ｌｎ＝ランタニド，Ｘ＝Ｐ， Ａｓ， Ｓｂ）の圧力誘起相転移

By use of synchrotron radiation, the powder x-ray diffraction of LnX (Ln=lanthanide, X=P, As and Sb) with a NaCl-type structure has systematically been studied at high pressures. Pressure-induced phase transitions of LnX were found at room temperature. The transition pressure is highest for LnP and lowest for LnSb. In this report the phase transitions of LnSb at high pressure are mainly described. The high-pressure form of LnSb is classified into three groups. The lighter LnSb (Ln=La, Ce Pr and Nd) have a tetragonal structure (distorted CsCl-type) at high pressures. The structure of the high-pressure phase of the middle LnSb (Ln=Sm, Gd and Tb) is unknown. The heavier LnSb (Ln=Dy, Ho, Er, Tm and Lu) shows the typical NaCl-CsCl transition at high pressures. The high-pressure structural behavior of LnX is discussed.

Investigation of hardness in tetrahedrally bonded nonmolecularCO2solids by density-functional theory

Stability and compressibility of several nonmolecular (polymeric) ${\mathrm{CO}}_{2}$ solids in structures analogous to those of ${\mathrm{SiO}}_{2}$ have been investigated with ab initio density-functional theory. Contrary to the recent experimental reports of a ``superhard'' high-pressure tridymite form of ${\mathrm{CO}}_{2},$ we find that metastable tetrahedrally bonded ${\mathrm{CO}}_{2}$ polymorphs, such as tridymite, cristobalite, and quartz, are relatively compressible, with bulk moduli K of only 1/2 to 1/3 of the reported experimental value. In addition, theory finds that the experimentally reported lattice parameters are not stable for ${\mathrm{CO}}_{2}$ ${P2}_{1}{2}_{1}{2}_{1}$ tridymite. Finally, none of the calculated x-ray spectra of the fully relaxed structures of ${\mathrm{CO}}_{2}$ polymorphs obtained from theory agrees with the experiments. The significant discrepancy between experiments and density-functional theory suggests that further studies on nonmolecular ${\mathrm{CO}}_{2}$ solids are necessary, and that the assumptions that density-functional theory can describe these materials correctly, or that the framework of the new nonmolecular ${\mathrm{CO}}_{2}$ solids contains only ${\mathrm{CO}}_{4}$ tetrahedra, must be re-examined.

A new high-pressure polymorph of NiSb 2

A new polymorph of NiSb 2 was obtained under high-pressure/temperature condition of 6 GPa and 550–650°C. The crystal structure is orthorhombic with the space group Pbca (No. 61), isostructural with the low-temperature form of NiAs 2 (pararammelsbergite). The crystallographic parameters were refined by the Rietveld analysis of the powder X-ray diffraction data ( a=0.62866(2) nm, b=0.63643(2) nm, c=1.23670(3) nm, Z=8). The structure can be regarded as an intermediate structure between the marcasite-type and the pyrite-type. The pararammelsbergite-type NiSb 2 is a high-pressure form of NiSb 2 and the density is slightly higher than that of ambient pressure form with the marcasite-type structure.

Evidence for ice VI as an inclusion in cuboid diamonds from high P-T near infrared spectroscopy

AbstractNear infrared absorption (NIR) spectra of natural morphologically cubic polycrystalline diamonds (cuboid) were obtained at room temperature, and the stretching plus bending combination band of molecular water was observed. The spectrum consisted of the main band at 5180 cm-1 due to liquid water and a shoulder at 5000 cm-1. The 5000 cm-1 band suggests the presence of a phase with stronger hydrogen bonding in inclusions in the diamond. This shoulder absorption decreased on heating to 120°C. The combination band of H2O at high pressure and temperature was measured using a resistively heated diamond cell and the pressure dependence of the peak position was obtained. Comparison with the present experimental results indicates that the spectral changes induced by heating of the cuboid corresponded to melting of a high-pressure form of ice, and the shoulder absorption at 5000 cm-1 arises from ice VI at 1.9 GPa. On the other hand, the liquid water, a main component of the fluid inclusions in the cuboid, was not under high pressure judging from the frequency of the combination band. This contrast might relate to the texture of the cuboid diamond. The spectral observation enables us to estimate the residual pressure of mantle fluid encapsulated in these diamonds. The diamond-cell data also provide high-P-T NIR fingerprint spectra that could be useful for identifying H2O phases and confining pressures in other samples.

Neutron scattering study of high-pressure phases obtained by thermobaric treatment

A technique of thermobaric quenching has been developed at the Institute of Solid State Physics RAS, which made it possible to prepare and study bulk samples of high-pressure phases in a metastable state at ambient pressure. The paper briefly discusses results of recent neutron scattering investigations of the crystal structure and lattice dynamics of high-pressure phases and forms of various alloys and compounds, such as the bulk amorphous alloys Ga-Sb, GaSb-Ge, Zn-Sb, Al-Ge, amorphous ice and metal hydrides TiH, Mn-H, PdH and NiH.