scholarly journals Synthesis of α-cristobalite-type CO2-SiO2under extreme conditions

2014 ◽  
Vol 70 (a1) ◽  
pp. C753-C753
Author(s):  
Julien Haines ◽  
Mario Santoro ◽  
Federico Gorelli ◽  
Roberto Bini ◽  
Olivier Cambon ◽  
...  
Keyword(s):  
Solid Solution ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Metastable Phase ◽  
Ambient Pressure ◽  
Small Variation ◽  
Unit Cell ◽  
Extreme Conditions ◽  
Oxygen Sublattice ◽  
Compact Structure

Extreme conditions change the behavior and reactivity of elements and compounds and permit the synthesis of novel materials. In the case of group IV oxides, molecular CO2and a network solid silica, which were considered to be incompatible, are found to react under HP-HT conditions. A crystalline CO2-SiO2solid solution was synthesized from molecular CO2and microporous silicalite SiO2at 16-22 GPa and temperatures above 4000 K in a laser heated diamond anvil cell [1]. Synchrotron X-ray diffraction data show that the crystal adopts a densely packed α-cristobalite structure (space group P41212) with carbon and silicon in 4-fold coordination. This occurs at pressures at which SiO2normally adopts a 6-fold coordinated rutile-type stishovite structure. The P-T conditions used in this study represent a compromise between the respective stabilities of 3- and 4-fold coordination in CO2and 4- and 6-fold coordination in SiO2. This solid solution can be recovered at ambient pressure at which the unit cell volume is 26% lower than that of α-cristobalite SiO2. This is due to the incorporation of much smaller carbon atoms, resulting in the collapse of the oxygen sublattice. The unit cell volume and the different C and Si sites identified in Raman spectroscopy are consistent with a C:Si ratio of 6(1):4(1). The tetragonal c/a ratio increases from 1.283 at 16 GPa to 1.303 at ambient pressure and is lower than that of SiO2due to the more compact structure of the new material and essentially corresponds to that of the dense rutile-type oxygen sublattice. This can explain the small variation in volume observed for this phase corresponding to a bulk modulus of about 240 GPa. Due to the incorporation of silicon atoms, this hard solid based on CO4tetrahedra can be retained as a metastable phase. This strongly modifies standard oxide chemistry and shows that carbon can enter silica giving rise to a new class of hard, light, carbon-rich oxide materials with novel physical properties.

Characterization of the pressure-induced second-order phase transition in the mixed-valence vanadate BaV6O11

2009 ◽  
Vol 65 (3) ◽  
pp. 326-333 ◽  
Author(s):  
Karen Friese ◽  
Yasushi Kanke ◽  
Andrzej Grzechnik
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Ambient Pressure ◽  
Mixed Valence ◽  
Volume Effect ◽  
Unit Cell ◽  
Additional Degree ◽  
Diamond Anvil

The pressure dependence of the structure of the mixed-valence vanadate BaV6O11 was studied with single-crystal X-ray diffraction in a diamond–anvil cell. The compressibility data could be fitted with a Murnaghan equation of state with the zero-pressure bulk modulus B 0 = 161 (7) GPa and the unit-cell volume at ambient pressure = 387.1 (3) Å^3 (B′ = 4.00). A phase transition involving a symmetry reduction from P63/mmc to P63 mc can be reliably detected in the high-pressure data. The estimated transition pressure lies in the range 1.18 < P c < 3.09 GPa. The transition leads to a breaking of the regular Kagomé net formed by part of the V ions. While in the ambient pressure structure all V—V distances in the Kagomé net are equal, they split into inter-trimer and intra-trimer distances in the high-pressure phase. In general, these changes are comparable to those observed in the corresponding low-temperature transition. However, the pressure-induced transition takes place at a lower unit-cell volume compared with the temperature-induced transition. Furthermore, overall trends for inter-trimer and intra-trimer V—V distances as a function of the unit-cell volume are clearly different for datapoints obtained by variation of pressure and temperature. The behavior of BaV6O11 is compared with that of NaV6O11. While in the latter compound the transition can be explained as a pure volume effect, in BaV6O11 an additional degree of freedom related to the valence distribution among the symmetrically independent vanadium sites has to be taken into account.

FexCu1-xBa2YCu2O7+y SUPERCONDUCTORS SYNTHESIZED BY HIGH PRESSURE

2005 ◽  
Vol 19 (01n03) ◽  
pp. 221-223 ◽  
Author(s):  
Y. H. LIU ◽  
G. C. CHE ◽  
K. Q. LI ◽  
Z. X. ZHAO ◽  
Z. Q. KOU ◽  
...  
Keyword(s):  
High Pressure ◽  
Cell Volume ◽  
Oxygen Content ◽  
Unit Cell Volume ◽  
Ambient Pressure ◽  
Lattice Parameter ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
X Ray ◽  
Oxygen Coordination

Systematic studies of x-ray diffraction(XRD), superconductivity and Mössbauer effect on Fe x Cu 1-x Ba 2 YCu 2 O 7+y ( x =0.00~0.70) superconductors synthesized by high pressure (HP) were summarized. All the HP-samples have tetragonal structure, smaller lattice parameter c and unit-cell volume than the AM-samples (synthesized by ambient pressure). The HP-samples have higher oxygen content than the AM-samples. Moreover, for the HP-sample with x =0.5, all of the Fe located in the CuO x chains have fivefold-oxygen coordination.

In situ XRPD study of the ambient-pressure synthesis of nonstoichiometric Ag3O from Ag–Ag2O thin films: Phase abundance, unit-cell parameters, and c/a as a function of temperature and time

2020 ◽  
Vol 35 (4) ◽  
pp. 247-261
Author(s):  
Paul J. Schields ◽  
Nicholas Dunwoody ◽  
David Field ◽  
Zachary Wilson
Keyword(s):  
Thin Films ◽  
Cell Volume ◽  
Room Temperature ◽  
Unit Cell Volume ◽  
Ambient Pressure ◽  
Thermal Reaction ◽  
Unit Cell ◽  
Unit Cell Parameters ◽  
Cell Parameters

Ag3O was synthesized by jet-milling magnetron-sputtered Ag–Ag2O thin films. Heating the jet-milled powders in air and N2 from 40 to 148 °C at ambient pressure produced Ag3O-rich powders. The phase composition and unit-cell parameters of the jet-milled powders were measured as a function of temperature with in situ X-ray powder diffraction experiments from −186 to 293 °C. Ag3O was also produced by ball milling and sonicating jet-milled films at ambient conditions. The phase composition, unit-cell parameters, and thermal-reaction rates indicate nonstoichiometric Ag3O was produced from the reaction of metastable, nonstoichiometric Ag2O (cuprite structure) and ccp Ag. The thermal expansion of Ag3O is anisotropic; below 25 °C, the a-axis expansion is about twice the c-axis expansion resulting in a negative slope of c/a(T). The reversal of the sign of c/a(T) near 25 °C is dramatic. The thermal reaction is arrested when the temperature is rapidly increased from ambient to 130 °C. Ag3O is metastable and decreases its unit-cell volume during kinetic decomposition to Ag when heated above ambient temperature in air and nitrogen. The relative volume expansion of Ag3O is about 80% less than Ag at room temperature and below. The suite of nonstoichiometric Ag3O produced by heating displays a linear relation between c/a and unit-cell volume at room temperature. The c/a and unit-cell volume of a hydrothermally grown Ag3O single crystal reported in a published structure determination was the Ag-rich, low-volume end member of the linear series. The c/a and unit-cell volume are sensitive indicators of the oxygen content and state of disorder.

scholarly journals Allanite at high temperature: effect of REE on the thermal behaviour of epidote-group minerals

2021 ◽  
Vol 48 (9) ◽  
Author(s):  
G. Diego Gatta ◽  
Francesco Pagliaro ◽  
Paolo Lotti ◽  
Alessandro Guastoni ◽  
Laura Cañadillas-Delgado ◽  
...  
Keyword(s):  
Cell Volume ◽  
Thermal Behaviour ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Atomic Scale ◽  
Elastic Behaviour ◽  
Positive Trend ◽  
Cell Parameters ◽  
Thermal Anisotropy ◽  
Different Temperatures

AbstractThe thermal behaviour of a natural allanite-(Ce) has been investigated up to 1073 K (at room pressure) by means of in situ synchrotron powder X-ray diffraction and single-crystal neutron diffraction. Allanite preserves its crystallinity up to 1073 K. However, up to 700 K, the thermal behaviour along the three principal crystallographic axes, of the monoclinic β angle and of the unit-cell volume follow monotonically increasing trends, which are almost linear. At T > 700–800 K, a drastic change takes place: an inversion of the trend is observed along the a and b axes (more pronounced along b) and for the monoclinic β angle; in contrast, an anomalous increase of the expansion is observed along the c axis, which controls the positive trend experienced by the unit-cell volume at T > 700–800 K. Data collected back to room T, after the HT experiments, show unit-cell parameters significantly different with respect to those previously measured at 293 K: allanite responds with an ideal elastic behaviour up to 700 K, and at T > 700–800 K its behaviour deviates from the elasticity field. The thermo-elastic behaviour up to 700 K was modelled with a modified Holland–Powell EoS; for the unit-cell volume, we obtained the following parameters: VT0 = 467.33(6) Å3 and αT0(V) = 2.8(3) × 10–5 K−1. The thermal anisotropy, derived on the basis of the axial expansion along the three main crystallographic directions, is the following: αT0(a):αT0(b):αT0(c) = 1.08:1:1.36. The T-induced mechanisms, at the atomic scale, are described on the basis of the neutron structure refinements at different temperatures. Evidence of dehydroxylation effect at T ≥ 848 K are reported. A comparison between the thermal behaviour of allanite, epidote and clinozoisite is carried out.

scholarly journals Study of Structural, Magnetic, and Mossbauer Properties of Dy2Fe16Ga1−xNbx (0.0 ≤ x ≤ 1.0) Prepared via Arc Melting Process

2021 ◽  
Vol 7 (3) ◽  
pp. 42
Author(s):  
Jiba N. Dahal ◽  
Kalangala Sikkanther Syed Ali ◽  
Sanjay R. Mishra
Keyword(s):  
Isomer Shift ◽  
Cell Volume ◽  
Intermetallic Compounds ◽  
Unit Cell Volume ◽  
Rietveld Analysis ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
X Ray ◽  
Arc Melting ◽  
Nb Content

Intermetallic compounds of Dy2Fe16Ga1−xNbx (x = 0.0 to 1.00) were synthesized by arc melting. Samples were investigated for structural, magnetic, and hyperfine properties using X-ray diffraction, vibration sample magnetometer, and Mossbauer spectrometer, respectively. The Rietveld analysis of room temperature X-ray diffraction data shows that all the samples were crystallized in Th2Fe17 structure. The unit cell volume of alloys increased linearly with an increase in Nb content. The maximum Curie temperature Tc ~523 K for x = 0.6 sample is higher than Tc = 153 K of Dy2Fe17. The saturation magnetization decreased linearly with increasing Nb content from 61.57 emu/g for x = 0.0 to 42.46 emu/g for x = 1.0. The Mössbauer spectra and Rietveld analysis showed a small amount of DyFe3 and NbFe2 secondary phases at x = 1.0. The hyperfine field of Dy2Fe16Ga1−xNbx decreased while the isomer shift values increased with the Nb content. The observed increase in isomer shift may have resulted from the decrease in s electron density due to the unit cell volume expansion. The substantial increase in Tc of thus prepared intermetallic compounds is expected to have implications in magnets used for high-temperature applications.

scholarly journals Neutron diffractometer covering protein crystals with large unit cell at J-PARC

2014 ◽  
Vol 70 (a1) ◽  
pp. C1746-C1746
Author(s):  
Kazuo Kurihara ◽  
Katsuaki Tomoyori ◽  
Taro Tamada ◽  
Ryota Kuroki
Keyword(s):  
Cell Volume ◽  
Unit Cell Volume ◽  
Structural Information ◽  
Unit Cell ◽  
Proton Accelerator ◽  
Neutron Guide ◽  
Time Dimension ◽  
Hydrogen Atoms ◽  
Large Unit ◽  
Large Unit Cell

The structural information of hydrogen atoms and hydration waters obtained by neutron protein crystallography is expected to contribute to elucidation of protein function and its improvement. However, many proteins, especially membrane proteins and protein complexes, have larger molecular weight and then unit cells of their crystals have larger volume, which is out of range of measurable unit cell volume for conventional diffractometers. Therefore, our group had designed the diffractometer which can cover such crystals with large unit cell volume (target lattice length: 250 Å). This diffractometer is dedicated for protein single crystals and has been proposed to be installed at J-PARC (Japan Proton Accelerator Research Complex). Larger unit cell volume causes a problem to separate spots closer to each other in spatial as well as time dimension in diffraction images. Therefore, our proposed diffractometer adopts longer camera distance (L2 = 800mm) and selects decoupled hydrogen moderator as neutron source which has shorter pulse width. Under the conditions that L1 is 33.5m, beam divergence 0.40and crystal edge size 2mm, this diffractometer is estimated to be able to resolves spots diffracted from crystals with a lattice length of 220 Å in each axis at d-space of 2.0 Å. In order to cover large neutron detecting area due to long camera distance, novel large-area detector (larger than 300mm × 300mm) with a spatial resolution of better than 2.5mm is under development. More than 40 these detectors plan to be installed, providing the total solid angle coverage of larger than 33%. For neutron guide, ellipsoidal supermirror is considered to be adopted to increase neutron flux at the sample position. The final gain factor of this diffractometer is estimated to be about 20 or larger as compared with BIX-3/4 diffractometers operated in the research reactor JRR-3 at JAEA (Japan Atomic Energy Agency) [1,2].

X-ray powder diffraction data for tetrazene nitrate monohydrate, C2H9N11O4

2021 ◽  
pp. 1-3
Author(s):  
J. Maixner ◽  
J. Ryšavý
Keyword(s):  
Cell Volume ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Powder Diffraction Data ◽  
Unit Cell Parameters ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters

X-ray powder diffraction data, unit-cell parameters, and space group for tetrazene nitrate monohydrate, C2H9N11O4, are reported [a = 5.205(1) Å, b = 13.932(3) Å, c = 14.196(4) Å, β = 97.826(3)°, unit-cell volume V = 1019.8(4) Å3, Z = 4, and space group P21/c]. All measured lines were indexed and are consistent with the P21/c space group. No detectable impurities were observed.

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