New view of the high-pressure behaviour of GdFeO3-type perovskites

2004 ◽  
Vol 60 (3) ◽  
pp. 263-271 ◽  
Author(s):  
J. Zhao ◽  
N. L. Ross ◽  
R. J. Angel
Keyword(s):  
High Pressure ◽  
Bond Distance ◽  
Bond Valence ◽  
Structural Behaviour ◽  
Cation Site ◽  
Higher Symmetry ◽  
Induced Changes ◽  
Cation Sites ◽  
Type Orthorhombic ◽  
Average Bond

Recent determinations of the structures of several GdFeO3-type orthorhombic perovskites (ABO3) show that the octahedra in some become more tilted with increasing pressure. In others the octahedra become less tilted and the structure evolves towards a higher-symmetry configuration. This variety of behaviour can be explained in terms of the relative compressibilities of the octahedral and dodecahedral cation sites in the perovskite structure. If the BO6 octahedra are less compressible than the AO12 sites then the perovskite will become more distorted with pressure, but the perovskite will become less distorted if the BO6 site is more compressible than the AO12 site. In this contribution we use the bond-valence concept to develop a model that predicts the relative compressibilities of the cation sites in oxide perovskites. We introduce the site parameter M i defined in terms of the coordination number N i , average bond length at room pressure R i , and the bond-valence parameters R 0 and B,M_i = ({R_i N_i }/ B)\exp [({{R_0 - R_i }) / B}].M i represents the variation in the bond-valence sum at the central cation in a polyhedral site because of the change of the average bond distance. Experimental data suggest that the pressure-induced changes in the bond-valence sums at the two cation sites within any given perovskite are equal. With this condition we show that the ratio of cation-site compressibilities is given by \beta _B /\beta _A = M_A /M_B. This model, based only upon room-pressure bond lengths and bond-valence parameters, correctly predicts the structural behaviour and some physical properties of the oxide perovskites that have been measured at high pressure.

scholarly journals High-pressure structural behaviour of nanocrystalline Ge

2007 ◽  
Vol 19 (15) ◽  
pp. 156217 ◽  
Author(s):  
H Wang ◽  
J F Liu ◽  
Y He ◽  
Y Wang ◽  
W Chen ◽  
...  
Keyword(s):  
High Pressure ◽  
Structural Behaviour

Leucite-pollucite structure-type variability and the structure of a synthetic end-member calcium wairakite (CaAl2Si4O12·2H2O)

1998 ◽  
Vol 62 (2) ◽  
pp. 165-178 ◽  
Author(s):  
C. M. B. Henderson ◽  
A. M. T. Bell ◽  
S. C. Kohn ◽  
C. S. Page
Keyword(s):  
Rietveld Analysis ◽  
Structure Type ◽  
Magic Angle Spinning ◽  
Resonance Spectroscopy ◽  
Magic Angle ◽  
Synthetic Sample ◽  
Cation Site ◽  
Wide Range ◽  
Angle Spinning ◽  
Cation Sites

AbstractThe structure of a synthetic end-member wairakite (CaAl2Si4O12·2H2O) has been determined using Rietveld analysis of high-resolution, synchrotron X-ray powder diffraction data, and 29Si and 27Al magic angle spinning nuclear magnetic resonance spectroscopy. The framework in the synthetic sample is more disordered than that in natural wairakite. Ca is distributed over the cavity cation sites M2, M12A, M12B in the approximate proportions 0.8:0.1:0.1, respectively, with M11 being vacant. 29Si MAS NMR data are consistent with about 80% of the Si occupying tetrahedral T11 and T12 sites linked to two Al atoms [Q4(2Al) silicons]. Tetrahedral and cavity cation site disorder are coupled so that Al mainly occupies T2 sites, with Ca in M12A and M12B being balanced by Al in T12A and T12B; T11A and T11B sites appear to only contain Si, in agreement with the M11 site being vacant. The crystal chemistries of the wide range of stoichiometries which crystallize with the leucite/pollucite structure-type are also reviewed, with particular attention being paid to the tetrahedral ordering configurations present in these phases, and the implications to crystallographic phase transitions.

scholarly journals Synthesis, Structure and Magnetic Properties of NiFe3O5

2022 ◽  
Author(s):  
Ka Hong ◽  
Elena Solana ◽  
Mauro Coduri ◽  
Clemens Ritter ◽  
Paul Attfield
Keyword(s):  
Exchange Interactions ◽  
Neutron Diffraction Data ◽  
Cation Site ◽  
Cell Parameters ◽  
Site Distribution ◽  
Rich Variety ◽  
Ordered Phases ◽  
The Rich ◽  
Cation Size ◽  
Cation Sites

Abstract A new CaFe3O5-type phase NiFe3O5 (orthorhombic Cmcm symmetry, cell parameters a = 2.89126(7), b = 9.71988(21) and c = 12.52694(27) Å) has been synthesised under pressures of 12-13 GPa at 1200 °C. NiFe3O5 has an inverse cation site distribution and reveals an interesting evolution from M2+(Fe3+ )2Fe2+O5 to Fe2+(M2+ 0.5Fe3+ 0.5)2Fe3+O5 distributions over three distinct cation sites as M2+ cation size decreases from Ca to Ni. Magnetic susceptibility measurements show successive transitions at 275, ~150, and ~20 K and neutron diffraction data reveal a series of at least three spin-ordered phases with evolving propagation vectors k = [0 0 0] [0 ky 0]  [½ ½ 0] on cooling. The rich variety of magnetically ordered phases in NiFe3O5 likely results from frustration of Goodenough-Kanamori exchange interactions between the three spin sublattices, and further interesting magnetic materials are expected to be accessible within the CaFe3O5-type family.

Quality changes in high pressure processed tan mutton during storage

2020 ◽  
pp. 108201322097078
Author(s):  
Dongdong Li ◽  
Yaling Peng ◽  
Yingmei Tao ◽  
Dunhua Liu ◽  
Haihong Zhang
Keyword(s):  
High Pressure ◽  
Troponin T ◽  
Quality Characteristics ◽  
Structural Proteins ◽  
Stress Relaxation Test ◽  
Test Application ◽  
Sds Page ◽  
Textural Changes ◽  
Induced Changes ◽  
Water Holding

The current study investigated the effects of high pressure (HP) treatment at 200 MPa and 500 MPa on quality characteristics of post-rigor tan mutton stored for 7 days at 4 °C, and textural changes were monitored during storage by means of the stress relaxation test. Application of 500 MPa high pressure significantly increased the elasticity and stiffness of meat after 7 days of storage ( P < 0.05), accompanied by a lighter and less red appearance and markedly enhanced centrifugal loss during storage campared to untreated ( P < 0.05). High pressure treatment at 200 MPa also substantially increased the lightness of samples throughout storage ( P < 0.05), and showed a significant increase in stiffness at the end of storage ( P < 0.05). Immunoblotting and electrophoresis (SDS-PAGE) analysis of key structural proteins revealed that myosin heavy chain denaturation began at 200 MPa, while actin denaturation occurred at 500 MPa. Troponin-T was continuously degraded in different treatments as storage progressed, and 200 MPa treatment and untreated represented similar degradation patterns, while 500 MPa treatment displayed more intense intact troponin-T at 38 kDa degradation. Results suggest that HP induced changes in cytoskeleton proteins, thereby affecting texture, water holding properties and lightness.

High Oxidation State Alkali-Metal Late-Transition-Metal Oxides

2000 ◽  
Vol 658 ◽  
Author(s):  
David B. Currie ◽  
Andrew L. Hector ◽  
Emmanuelle A. Raekelboom ◽  
John R. Owen ◽  
Mark T. Weller
Keyword(s):  
High Pressure ◽  
Solid State ◽  
Transition Metal Oxides ◽  
Late Transition Metal ◽  
High Oxidation State ◽  
Powder Neutron Diffraction ◽  
Nmr Study ◽  
High Oxidation ◽  
Late Transition ◽  
Cation Sites

ABSTRACTLi2NaCu2O4 has been prepared by solid state reaction under high-pressure (250 Atm) oxygen. A structural study, using time-of-flight powder neutron diffraction on a sample made with 7Li, shows a material isostructural with Li3Cu2O4, with sodium occupying the octahedral and lithium the tetrahedral A-cation sites. A 7Li MAS-NMR study of Li3Cu2O4, Li2NaCu2O4 and Li2CuO2 has been used to confirm the Li/Na site ordering.

scholarly journals High-pressure study of binary thorium compounds from first principles theory and comparisons with experiment

2014 ◽  
Vol 70 (3) ◽  
pp. 459-468 ◽  
Author(s):  
V. Kanchana ◽  
G. Vaitheeswaran ◽  
A. Svane ◽  
S. Heathman ◽  
L. Gerward ◽  
...  
Keyword(s):  
High Pressure ◽  
Equations Of State ◽  
Structural Phase ◽  
Experimental Results ◽  
Full Potential ◽  
Generalized Gradient ◽  
Structural Behaviour ◽  
Cscl Type ◽  
Lmto Method ◽  
Thorium Compounds

The high-pressure structural behaviour of a series of binary thorium compounds ThX(X= C, N, P, As, Sb, Bi, S, Se, Te) is studied using the all-electron full potential linear muffin-tin orbital (FP-LMTO) method within the generalized gradient approximation (GGA) for the exchange and correlation potential. The calculated equlibrium lattice parameters and bulk moduli, as well as the equations of state agree well with experimental results. New experiments are reported for ThBi and ThN. Calculations are performed for the ThXcompounds in the NaCl- and CsCl-type crystal structures, and structural phase transitions from NaCl to CsCl are found in ThP, ThAs, ThSb and ThSe at pressures of 26.1, 22.1, 8.1 and 23.2 GPa, respectively, in excellent agreement with experimental results. ThC, ThN and ThS are found to be stable in the NaCl structure, and ThBi and ThTe in the CsCl structure, for pressures below 50 GPa. The electronic structures of the ThXcompounds are studied using the quasiparticle self-consistentGWmethod (G: Green function,W: dynamically screened interaction).

Ca10V5.2Fe0.8O24, a Novel Oxometalate with Discrete Complex Anions

2003 ◽  
Vol 58 (11) ◽  
pp. 1112-1116 ◽  
Author(s):  
Kurt O. Kleppa ◽  
Norbert A. Harringer ◽  
Hubert Preßlinger
Keyword(s):  
Crystal Structure ◽  
Single Crystals ◽  
Bond Distance ◽  
Structure Type ◽  
The Other ◽  
Nominal Composition ◽  
Average Bond ◽  
Complex Anions ◽  
Trigonal Prismatic ◽  
Discrete Complex

Abstract Lustrous needle shaped prismatic single crystals of the new compound Ca10V5.2Fe0.8O24 were obtained out of a sample with nominal composition Ca2Fe1.6V0.4O5 prepared at 1400 °C. The crystals are opaque and stable to humid air. Ca10V5.2Fe0.8O24 crystallizes with a new structure type, space group Pnma with a = 6.803(3), b = 16.015(8), c = 10.418(7)Å , Z = 2, R = 0.041. The crystal structure is characterized by two mononuclear tetrahedral species, MO4, which differ significantly from each other with respect to their M-O bond lengths. One with an average bond distance of 1.709(8)Å represents an orthovanadate ion. The other with a significantly larger value d(M-O) = 1.744(6) Å corresponds to a mixed occupation of its centre according to [V0.8Fe0.2O4]3.5−. In the crystal structure the complex anions are arranged in separate sheets parallel to the (010) plane. They are separated from each other by three crystallographically independent Ca2+ ions which are each coordinated by 7 oxygen atoms in distorted pentagonal bipyramidal and trigonal prismatic configurations, respectively.

scholarly journals High-pressure structural behaviour of HoVO4: combined XRD experiments andab initiocalculations

2014 ◽  
Vol 26 (26) ◽  
pp. 265402 ◽  
Author(s):  
Alka B Garg ◽  
D Errandonea ◽  
P Rodríguez-Hernández ◽  
S López-Moreno ◽  
A Muñoz ◽  
...  
Keyword(s):  
High Pressure ◽  
Structural Behaviour

scholarly journals Double salt crystal structure of hexasodium hemiundecahydrogenα-hexamolybdoplatinate(IV) heminonahydrogenα-hexamolybdoplatinate(IV) nonacosahydrate: dihydrogen disordered-mixture double salt

2015 ◽  
Vol 71 (10) ◽  
pp. 1250-1254 ◽  
Author(s):  
Hea-Chung Joo ◽  
Ki-Min Park ◽  
Uk Lee
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Hydrothermal Reaction ◽  
Bond Distance ◽  
Bond Valence ◽  
Double Salt ◽  
Charge Balance ◽  
Salt Crystal ◽  
Bond Valence Sum ◽  
Difference Fourier

The title double salt containing two distinct, differently protonated hexamolybdoplatinate(IV) polyanions, Na6[H5.5α-PtMo6O24][H4.5α-PtMo6O24]·29H2O, has been synthesized by a hydrothermal reaction atcapH 1.80. The positions of the H atoms in the polyanions were established from difference Fourier maps and confirmed by the interpolyanion hydrogen bonds, bond-distance elongation, and bond-valence sum (BVS) calculations. The fractional numbers of H atoms in each polyanion are required for charge balance and in order to avoid unrealistically short H...H distances in the interpolyanion hydrogen bonds. Considering the disorder, the refined formula of the title polyanion, {[H5.5α-PtMo6O24]; polyanion (A) and [H4.5α-PtMo6O24]; polyanion (B)}6−, can be rewritten as a set of real formula,viz. {[H6α-PtMo6O24]; polyanion (A). [H4α-PtMo6O24]; polyanion (B)}6−and {[H5α-PtMo6O24]; polyanion (A). [H5α-PtMo6O24]; polyanion (B)}6−. The polyanion pairs both form dimers of the same formula,viz. {[H10α-Pt2Mo12O48]}6−connected by seven interpolyanion O—H...O hydrogen bonds.

scholarly journals Synthesis and superstructural characterization of Fe1.89Mo4.11O7

1994 ◽  
Vol 9 (4) ◽  
pp. 891-897 ◽  
Author(s):  
George L. Schimek ◽  
Robert E. McCarley ◽  
L. Scott Chumbley
Keyword(s):  
Structure Type ◽  
Tetrahedral Coordination ◽  
X Ray Diffraction ◽  
Cation Site ◽  
X Ray ◽  
Transmission Electron ◽  
The Family ◽  
Regular Arrangement ◽  
Cation Sites

Superstructuring in the new compound Fe1.89Mo4.11O7 has been elucidated by transmission electron microscopy. This compound is a member of the family M2MO4O7 and has both iron and molybdenum atoms occupying octahedrally coordinated sites in the structure, represented by Fet(Fe0.89M0.11)0Mo4O7. The superstructuring, detected only by electron diffraction, involved tripling of all three lattice parameters of the subcell. The subcell was structured by single crystal x-ray diffraction [Imma, no. 74, a = 5.9793(5) Å, b = 5.7704(4) Å, and c = 17.036(1) Å]. This structure type contains a close-packed arrangement of Mo4O7 units, which are infinite chains of trans edge-shared molybdenum octahedra running parallel to b*. Two different coordination environments are observed for the cations. Parallel to the a* direction, infinite edge-sharing MO6 (M = 89% Fe or 11% Mo) octahedra are observed. The second cation site, with nearly tetrahedral coordination by oxygen, is filled solely by iron. The superstructure can be rationalized by a regular arrangement of iron and molybdenum atoms in the octahedrally coordinated cation sites.

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