High-pressure Form Research Articles

斜方晶ZrO<SUB>2</SUB>(高圧相)の格子定数と密度に対する微量Y<SUB>2</SUB>O<SUB>3</SUB>添加の効果

斜方晶ZrO<SUB>2</SUB>(高圧相)の格子定数と密度に対する微量Y<SUB>2</SUB>O<SUB>3</SUB>添加の効果

Characterization of the electrocrystallization products of the mixed-donor system ET:MET (1:1) / I 3 / TCE: How to get crystals with the ordered ß ∗-(ET) 2I 3 structure and a T c of 4.6 K without applied pressure

Crystals that result from the electrocrystallization of a 1:1 mixture of the organic donor molecules ET and MET with the I 3- anion are superconducting at ambient pressure, T c = 4.6 K. Single crystal X-ray diffraction investigations (298 K) show that the crystals are ß-(ET) 2I 3 and little or no MET is incorporated. However, at 125 K no modulated structure is observed, instead the ethylene groups of the ET molecule are ordered. The conformation of the ET molecule is the same as that observed in ß ∗-(ET) 2I 3, the high pressure form of ß-(ET) 2I 3, with T c ∼ 8 K.

Preparation and crystal structures of some complex sulphides at high pressures

The NH 4CdCl 3 structure is a high-pressure form for some complex sulphides. Sr(Ti 1−xZr x)S 3, a mixture of hexagonal SrTiS 3 (BaNiO 3 structure) and orthorhombic SrZrS 3 (GdFeO 3 structure) at the ambient pressure, transforms to the orthorhombic NH 4CdCl 3 structure by heating at 1000°C under a pressure of 60 kbar. The NH 4CdCl 3 structure is also a high-pressure form of BaSnS 3 and SrSnS 3. In Ba(Ti 1−xZr x)S 3 having the same structural form as Sr(Ti 1−xZr x)S 3 at 0 kbar, only Ba(Ti 0.25Zr 0.75)S 3 transforms to a tetragonal perovskite structure at 900°C and 60 kbar. The volume change in Sr(Ti 1−xZr x)S 3 from the state at 0 kbar to the NH 4CdCl 3 structure is much larger than that of Ba(Ti 0.25Zr 0.75)S 3 from 0 to 60 kbar form, suggesting that Ba(Ti 1−xZr x)S 3 will also posess the NH 4CdCl 3 structure at higher pressures.

Thermodynamic properties of silicalite SiO 2

Silicalite, a polymorph of SiO 2, is a new and interesting molecular-sieve material. Low-temperature (5 to 350 K) heat-capacity, flourine-combustion, high-temperature (350 to 1500 K) drop-calorimetric, and reaction-calorimetric with HF(aq) measurements have been performed on this material. At T′ = 298.15 K, Δ f H m o( T′) = −(905.20±0.84) kJ·mol −1; C p, m o( T′) = (46.34±0.23) J·K −1·mol −1; { Δ 0 T′ S m o( T′)} = (46.29±0.23) J·K −1·mol −1; and Δ f G m o( T′) = −(852.23±0.84) kJ·mol −1. The enthalpies of reaction with 24.4 mass per cent hydrofluoric acid of silicalite at mass concentrations of 0.5, 1, 2, and 4 g·dm −3 were determined to be −(144.91±0.23), −(144.80±0.10), −(145.07±0.12), and −(145.06±0.14) kJ·mol −1, respectively. The enthalpies of reaction of silicalite with 20.1 and 15.0 mass per cent hydrofluoric acid at a silicalite mass concentration of 1 g·dm −3 were determined to be −(143.85±0.19) and −(142.68±0.08) kJ·mol −1, respectively. Because silicalite reacts rapidly with HF(aq) at 298.15 K, it has potential as a reference material for thermochemical measurements on inorganic silicates and silicate minerals. Silicalite is less stable than quartz, cristobalite, or tridymite, but more stable than SiO 2(glass) or the high-pressure forms coesite or stishovite.

The crystal structure of epitaxially grown SnO 2 thin films

It is shown by computer simulation of the transmission electron diffraction patterns and by structural considerations that the recently reported thin film form β-SnO 2 is equivalent to the high pressure form SnO 2-II. It crystallizes in a columbite-like structure either under the influence of the substrate in the case of epitaxial oxidation of α-SnO to SnO 2 or under the influence of volume contraction conditioned by enhanced pressure and/or temperature during the cassiterite- columbite transformation. The columbite-brookite-cassiterite structural relationship is given and the possibility of the existence of a thin film fluorite-like polymorph is discussed.

Crystal structure of coesite, a high-pressure form of silica, at 15 and 298 K from single-crystal neutron and x-ray diffraction data: test of bonding models

The crystal structure of a natural coesite from an eclogite rock fragment in the Roberts Victor kimberlite, South Africa, was determined at 15 K by neutron diffraction (a = 7.1357 (13) A, b = 12.3835 (26) A, c = 7.1859 (11) A, ..beta.. = 120.375 (16)/sup 0/, C2/c), and at approx.298 K by X-ray diffraction. Cell dimensions measured by neutron diffraction at 292 K (7.1464 (9), 12.3796 (19), and 7.1829 (8) A, 120.283 (9)/sup 0/) differed from those determined by X-ray diffraction, probably because of a systematic absorption error for the latter. The strongly anisotropic nature of the thermal expansion is explained qualitatively by the relatively large changes (approx.1%) in the distances between the nonbonded oxygen neighbors and the relatively small changes of Si-O-Si and O-Si-O angles in the compact three-dimensional framework. There is a good, but not perfect, negative correlation between the eight independent Si-O distances and the five independent values for sec theta(Si-O-Si) at 15 K. It is weaker than that for 298 K, and the scatter from a straight-line prediction from molecular-orbital models for small clusters (e.g., H/sub 6/Si/sub 2/O/sub 7/) implies that it is desirably to consider additional forces, including repulsive forces between nonbonded oxygen neighbors.more » The combined at a for Si-O and Si-O-Si in coesite, quartz, and cristobalite at 10-15 K show less scatter than those for approx.298 K, in accordance with the greater thermal response of framework geometry in the more open structures.« less

Unit cell parameters and densities of non-doped and 2mol% Y2O3 doped orthorhombic (high pressure form) ZrO2.

Unit cell parameters of non-doped ZrO2 (monoclinic + orthorhombic: high pressure form) and 2 mol% Y2O3 doped ZrO2 (monoclinic + orthorhombic + tetragonal) samples obtained by high pressure experiments were refined, together with those of starting materials, by the technique of whole-powder-pattern fitting without reference to a structural model. The monoclinic-to-orthorhombic transformation of ZrO2 accompanies the increase of density by 0.25 to 0.26 g/cm3. The tetragonal form has a slightly higher density than the orthorhombic form: the difference between the two phases is only 0.03 g/cm3.

Annealing and relaxation in the high-pressure phase of amorphous SiO2.

In a recent article [Phys. Rev. Lett. 52, 2379 (1984)] it was reported that irreversible changes occur in the Brillouin spectra of $a\ensuremath{-}\mathrm{Si}{\mathrm{O}}_{2}$ that has been subjected to pressures above \ensuremath{\sim} 9 GPa. Based on Raman spectra from the recovered samples it was concluded that the new "polymorph" was also amorphous. Here we report on relaxation and annealing effects in this high-pressure form which leave no doubt as to its amorphous nature.

Crystal structure of the high-pressure form of BiVO4

Abstract The crystal structure of BiVO4, which has a monoclinic, distorted scheelite structure at ambient conditions, has been determined above the high-pressure transition at 1.6 and 4.3 GPa, and 23°C. At these pressures BiVO4 has the tetragonal scheelite structure, which is also observed at high temperature above 250°C at room pressure. Vanadium tetrahedra remain rigid with no significant change in size at high pressure. Reduction of unit-cell volume is principally a result of Bi-O polyhedral compression. This behavior is similar to that observed for other scheelite-type compounds, in which tetrahedra are rigid and compression occurs in the 8-coordinated polyhedron.

Optical properties of Eu 3+-doped tetragonal lutetium oxyhydroxide

The UV and dye-laser-excited luminescence spectra of the Eu 3+-doped tetragonal high-pressure form of LuOOH were measured at 77 and 300 K. The analysis of the emission spectra yielded a complete crystal-field (c.f.) energy-level scheme for the 7F 0–4 levels. The simulation of c.f. splittings was conducted in the 25 Stark-level basis set in C 2 v and C 2 symmetries. A satisfactory simulation was obtained only with the C 2 c.f. parameter set. A comparison with the results of a c.f. analysis of the monoclinic form of LuOOH was also carried out.

On the possibility of Pr III having a thcp structure

Crystallographic calculations have been carried out for a triple hexagonal close-packed (thcp) structure using data for Pr III, a high-pressure form shown by praseodymium metal. McMahan and Young proposed thcp as an additional high-pressure phase in the rare earth metals structural sequence. As applied to Pr III data at 14.4 GPa pressure, this structure type accounts for most but not all of the diffraction lines. Thus, we are unable to establish conclusively that Pr III has a thcp structure. However, it is shown that the thcp structure fits the Pr III data as reasonably as other structural forms proposed by other authors.

Growth Rate of Polyethylene Single Crystals at High Pressure

The growth kinetics of extended-chain single crystals (ECSC) of polyethylene are studied. The results of an expertment on the growth rate and the structure of the high-pressure form suggest that the segments in the crystal slide along their own axes very easily and that the ends of the segments form uneven contour surfaces so as to minimize the boundary free energy. On such a secondary nucleus model, we assume that the elementary step of the growth is the “creeping in” of a repeating unit linked directly to a crystalline segment through the boundary surface of the nucleus. We have the normal growth rate V∝=Texp (-G*/3 kT), where ΔT is the degree of supercooling and G* is the least free energy of formation of a critical nucleus. By fitting this relation with the experimental one, we obtain G*=134/ΔT (kJ/mol) at 300 MPa, a value 1/14 of that at 0.1 MPa.

A new high pressure form of PtO2

The existence of β'-PtO2, which is a new modification of platinum dioxide with the rutile structure, is reported. The synthesis was carried out in a belt-type apparatus at a pressure of 40–60 kbar and a temperature of 500 °C. The starting materials were H2Pt(OH)6 or α-PtO2 with HClO3 or BaO2 to provide an oxidizing atmosphere. The new phase, which is a microcrystalline black powder, was characterized by X-ray powder diffraction, electron diffraction and IR spectroscopy. The X-ray powder diffraction pattern was completely indexed on a tetragonal basis and the calculated unit cell parameters were a = 4.485(1) Å and c = 3.130(2) Å. These parameters indicate an undistorted rutile structure. Thermogravimetric experiments were carried out on the new compound to study its stability field. The differences among the structural and physical properties of the various PtO2 phases are discussed.

ESR of Cu 2+ in the high pressure form of Cd 3(PO 4) 2

ESR spectra of polycrystalline Cu 2+ doped samples of the high pressure phase of Cd 3(PO 4) 2 were characteristic of the existence of two different paramagnetic centres. The spin—Hamiltonian constants of both defects were determined. Only two of the three possible substitutional cation sites are occupied by copper ions.

Rheology of ices: a key to the tectonics of the ice moons of Jupiter and Saturn

The polymorphic varieties of water ice are important rock-forming minerals in the outer Solar System. The Voyager 1 and 2 missions have shown that most of the ice moons of Jupiter and Saturn have had some form of tectonic or internal activity. Understanding of the tectonics and building reasonable models of the interior of these planets depend on our knowledge of the Theological properties and viscosity of high-pressure and low-temperature forms of ice.

Structure of lithium borate and strontium borate glasses with high modifier contents

The structure of lithium borate and strontium borate glasses with high Li 2O and SrO contents was examined using the experimental results of ESR and the optical absorption of Cu 2+ ions, and the Mössbauer spectra of Fe 3+ ions and Raman spectra of these glasses. The results indicate the existence of non-bridging oxygens belonging to orthoborate and pyroborate groups, structural groups of diborate and high pressure forms of metaborate above 30 mol% of the modifier contents in these glasses. Among these four structural groups, the diborate group rapidly decreased with an increase of the modifier contents, while the other three groups increased with an increase of the modifier contents.

ChemInform Abstract: STABILITIES OF STRUCTURES RELATED TO THE HIGH‐PRESSURE FORM OF GERMANIUM PHOSPHIDE, WHICH MAY BE DERIVED FROM ROCK SALT BY BOND BREAKING

Chemischer InformationsdienstVolume 13, Issue 28 Physical Inorganic Chemistry ChemInform Abstract: STABILITIES OF STRUCTURES RELATED TO THE HIGH-PRESSURE FORM OF GERMANIUM PHOSPHIDE, WHICH MAY BE DERIVED FROM ROCK SALT BY BOND BREAKING J. H. BULARZIK, J. H. BULARZIKSearch for more papers by this authorJ. K. BURDETT, J. K. BURDETTSearch for more papers by this authorT. J. MCLARNAN, T. J. MCLARNANSearch for more papers by this author J. H. BULARZIK, J. H. BULARZIKSearch for more papers by this authorJ. K. BURDETT, J. K. BURDETTSearch for more papers by this authorT. J. MCLARNAN, T. J. MCLARNANSearch for more papers by this author First published: July 13, 1982 https://doi.org/10.1002/chin.198228001Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume13, Issue28July 13, 1982 RelatedInformation

Stabilities of structures related to the high-pressure form of germanium phosphide, which may be derived from rock salt by bond breaking

Stabilities of structures related to the high-pressure form of germanium phosphide, which may be derived from rock salt by bond breaking

A high-pressure form of lithium vanadium dioxide –a 2 × 2 × 2 NaCl superstructure

A high-pressure form of lithium vanadium dioxide –a 2 × 2 × 2 NaCl superstructure

Electrical behavior of Eu at very high pressures and low temperatures

Normally Eu has a valence of two while its Periodic-Table neighbors Sm and Gd have valences of three. There is theoretical reason to believe that some densification of Eu by pressure would shift the balance of the $4f$ and $5d$ electrons to promote it to a valence of three and a different crystal structure. Some theoretical treatments suggest that the high-pressure form of Eu might be superconducting at sufficiently low temperatures. In our experiments, the electrical resistance of Eu specimens was observed to pressures above 400 kbar and temperature down to 2.3 K. In this range, no superconductivity was observed. Based upon reproducible discontinuities of $\frac{\mathrm{dR}}{\mathrm{dT}}$ and of $\frac{\mathrm{dR}}{\mathrm{dP}}$, and the reported observations of others, a tentative $P$,$T$ phase diagram is proposed. As the pressure is varied there is one phase below about 125-150 kbar and a different phase above. As the temperature is increased in the low-pressure phase there is a magnetic ordering transformation in the 90-75-K region, and in the high-pressure phase there is a change at about 150 K, the physical nature of which has not been established.