Incommensurate crystal structure of PbHfO3

2020 ◽  
Vol 76 (1) ◽  
pp. 7-12 ◽  
Author(s):  
Alexei Bosak ◽  
Volodymyr Svitlyk ◽  
Alla Arakcheeva ◽  
Roman Burkovsky ◽  
Vadim Diadkin ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Amplitude Modulation ◽  
Intermediate Phase ◽  
Unit Cell ◽  
Lead Ions ◽  
Diffraction Experiment ◽  
Pure Compound ◽  
Synchrotron Diffraction ◽  
Structure Modulation ◽  
Modulation Vector

Controversy in the description/identification of so-called intermediate phase(s) in PbHfO3, stable in the range ∼420–480 K, has existed for a few decades. A synchrotron diffraction experiment on a partially detwinned crystal allowed the structure to be solved in the superspace group Imma(00γ)s00 (No. 74.2). In contrast to some previously published reports, in the pure compound only one distinct phase was observed between Pbam PbZrO3-like antiferroelectric and Pm3m paraelectric phases. The modulation vector depends only slightly on temperature. The major structure modulation is associated with the displacement of lead ions, which is accompanied by a smaller amplitude modulation for the surrounding O atoms and tilting of HfO6 octahedra. Tilting of the octahedra results in a doubling of the unit cell compared with the parent structure.

scholarly journals Crystal structure interconnections in a family of hydrated phosphate-sulfates

2014 ◽  
Vol 70 (a1) ◽  
pp. C1091-C1091
Author(s):  
Olga Yakubovich ◽  
Ian Steele ◽  
Oxana Karimova
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Unit Cell ◽  
Crystal Chemical ◽  
Synchrotron Diffraction ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Triclinic Structure ◽  
Hydrated Phosphate ◽  
Fibrous Mineral

The phosphate-sulfate family incorporates several water-containing hypergene minerals with various structures. We determined the crystal structure of lately discovered [1] fibrous mineral arangasite, [Al2F(H2O)6(PO4)(SO4)]·3(H2O) using single-crystal synchrotron diffraction at 100 K (a =7.073(1), b=9.634(2), c=10.827(2) Å, β=79.60(1)0, P2/a, Z=2). Its crystal chemical interpretation has allowed us to reveal some interesting features in a title group of compounds. The arangasite crystal structure is dominated by chains extending in the [100] direction and built of pairs of corner-shared Al octahedra joined through bridging F atoms and P tetrahedra. They alternate in the [001] with S tetrahedra forming layers parallel to the ac plane through a system of hydrogen bonds. Along [010] the complex layers are separated by layers of H2O molecules. Hydrogen bonding serves here as the only mechanism providing linkage between the main structural fragments. The Al/ P chains are topologically identical to the chains built from Fe octahedra and P tetrahedra in the triclinic structure of destinezite, Fe2(OH)(PO4)(SO4)(H2O)6[2]. The repeating subunit of both chains consists of two octahedra and one tetrahedron sharing vertices. A main difference among the chains arises from their chemistry; Al octahedra in arangasite form pairs by sharing the F vertex of neighboring polyhedra, whereas pairs of Fe octahedra in destinezite are linked together through the oxygen vertex of an OH group. As a result, the larger size of the Fe octahedra compared to Al octahedra causes a larger c = 7.31 Å along the chain in destinezite. Additional SO4tetrahedra here are attached to these chains along their periphery through an oxygen vertex bridge with Fe octahedra. The monoclinic sanjuanite, Al2(PO4)(SO4)(OH)(H2O)9structure [3] is composed of Al/P chains, parallel to a = 6.11 Å. These chains are also built from three-member units that include corner-sharing pairs of octahedra connected by PO4tetrahedron, but they are not topologically equivalent to the chains in the arangasite and destinezite structures. Similar to arangasite, sulfate groups and H2O molecules reside between chains in the sanjuanite structure with hydrogen bonding. Thus, similar the crystal chemical formulae of sanjuanite and arangasite differ with respect to the (OH) → F substitution, which results in contrasting unit cell parameters. Note, that the unit cell volume of sanjuanite, is twice as large as arangasite.

The crystal structure of eugaAl

1992 ◽  
Vol 50 (2) ◽  
pp. 1452-1453
Author(s):  
H. Brigitte Krause ◽  
Yonglin Qian
Keyword(s):  
Crystal Structure ◽  
Electron Microscope ◽  
Zone Axis ◽  
Unit Cell ◽  
Polycrystalline Specimen ◽  
Lattice Constants

A polycrystalline specimen of nominal formula EuGaAl with unknown crystal structure was investigated by various electron microscope techniques; EDS-, SED-, and CBED data were taken on a Philips 400 electron microscope operated at 100kV, HREM data on a Hitachi 9000 microscope operated at 300kV. The EDS data confirmed the composition for the bulk of the material but, in addition, revealed particles with other fractions of the elements. Only the EuGaAl particles were further investigated. The unit cell was determined to be orthorhombic with a ratio: a/b=0.969(2) , a/c=0.234(2) and b/c=0.234(2). The lattice constants are a=4.54(5)Ȧ, b=4.68Ȧ and c=19.97(20)Ȧ. Based on systematic extinctions for hkl reflections with h+l=2n+l, the unit cell was found to be b-centered. CBED patterns of the [001], [100], and [010] zone axes are shown in Fig. 1. The zone axis patterns are in agreement with the above stated data except for diffused (2m+l,2n+l,0)- reflections, not compatible with the above stated systematic absences. But these occurred only occasionally in conjunction with a complicated noncommensurate superlattice pattern.

scholarly journals Crystal Structure Refinements of Four Monazite Samples from Different Localities

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1028 ◽  
Author(s):  
M. Mashrur Zaman ◽  
Sytle M. Antao
Keyword(s):  
Crystal Structure ◽  
Electron Probe ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
X Ray ◽  
Cell Parameters ◽  
Large Unit Cell ◽  
A Site

This study investigates the crystal chemistry of monazite (APO4, where A = Lanthanides = Ln, as well as Y, Th, U, Ca, and Pb) based on four samples from different localities using single-crystal X-ray diffraction and electron-probe microanalysis. The crystal structure of all four samples are well refined, as indicated by their refinement statistics. Relatively large unit-cell parameters (a = 6.7640(5), b = 6.9850(4), c = 6.4500(3) Å, β = 103.584(2)°, and V = 296.22(3) Å3) are obtained for a detrital monazite-Ce from Cox’s Bazar, Bangladesh. Sm-rich monazite from Gunnison County, Colorado, USA, has smaller unit-cell parameters (a = 6.7010(4), b = 6.9080(4), c = 6.4300(4) Å, β = 103.817(3)°, and V = 289.04(3) Å3). The a, b, and c unit-cell parameters vary linearly with the unit-cell volume, V. The change in the a parameter is large (0.2 Å) and is related to the type of cations occupying the A site. The average <A-O> distances vary linearly with V, whereas the average <P-O> distances are nearly constant because the PO4 group is a rigid tetrahedron.

LaMg11 with a giant unit cell synthesized by hydrogen metallurgy: Crystal structure and hydrogenation behavior

2010 ◽  
Vol 58 (7) ◽  
pp. 2510-2519 ◽  
Author(s):  
Roman V. Denys ◽  
Andrey A. Poletaev ◽  
Jan Ketil Solberg ◽  
Boris P. Tarasov ◽  
Volodymyr A. Yartys
Keyword(s):  
Crystal Structure ◽  
Unit Cell

The crystal chemistry of the uranyl carbonate mineral grimselite, (K, Na)3Na[(UO2)(CO3)3](H2O), from Jáchymov, Czech Republic

2012 ◽  
Vol 76 (3) ◽  
pp. 443-453 ◽  
Author(s):  
J. Plášil ◽  
K. Fejfarová ◽  
R. Skála ◽  
R. Škoda ◽  
N. Meisser ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Czech Republic ◽  
Structure Refinement ◽  
Unit Cell ◽  
Carbonate Mineral ◽  
X Ray Diffraction ◽  
The Czech Republic ◽  
Cell Parameters ◽  
Uranyl Carbonate ◽  
Diffraction Peaks

AbstractTwo crystals of the uranyl carbonate mineral grimselite, ideally K3Na[(UO2)(CO3)3](H2O), from Jáchymov in the Czech Republic were studied by single-crystal X-ray diffraction and electron-probe microanalysis. One crystal has considerably more Na than the ideal chemical composition due to substitution of Na into KO8 polyhedra; the composition of the other crystal is nearer to ideal, and similar to synthetic grimselite. The presence of Na atoms in KO8 polyhedra, which are located in channels in the crystal structure, reduces their volume, and as a result the unit-cell volume also decreases. Structure refinement shows that the formula for the sample with the anomalously high Na content is (K2.43Na0.57)Σ3.00Na[(UO2)(CO3)3](H2O). The unit-cell parameters, refined in space group P2c, are a = 9.2507(1), c = 8.1788(1) Å, V = 606.14(3) Å3 and Z = 2. The crystal structure was refined to R1 = 0.0082 and wR1 = 0.0185 with a GOF = 1.33, based on 626 observed diffraction peaks [Iobs>3σ(I)].

Pseudo-C11b Phase Formation of Titanium Disilicide During the C49 to C54 Transition

1997 ◽  
Vol 481 ◽  
Author(s):  
Patrick L. Smith ◽  
Richard Ortega ◽  
Bill Brennan
Keyword(s):  
Thin Films ◽  
Plane Wave ◽  
Intermediate Phase ◽  
Unit Cell ◽  
Silicon Substrates ◽  
Unit Cell Parameters ◽  
Titanium Disilicide ◽  
Cell Parameters ◽  
Chemical Signatures ◽  
Pseudo Potential

ABSTRACTThe formation of TiSi2 thin films using the SALICIDE process on doped and undoped silicon substrates was studied. XRD TEM, AES, RBS and four probe Rs were used to characterize the material. Unit cell parameters and energetics were determined. Results confirm electrical and chemical signatures consistent with the known C49 conversion to C54. However, XRD indicated a structurally different intermediate phase occurs during the C49 to C54 transformation. Modeling was performed based on C11b structure (14/mmm) type, with the Ti and Si atoms arranged similarly to those in MoSi2. The unit cell was determined to be a = 4.428 Å, b = 4.779 Å, c = 9.078 Å with a Fmmm space group and total pseudo-potential plane wave calculations based on crystallographic simulations of −103.96 ev/Atom.

NQR and Crystal Structure of 4,5-Dichloroimidazole, C3H2N2Cl2

1992 ◽  
Vol 47 (1-2) ◽  
pp. 177-181 ◽  
Author(s):  
Shi-Qi Dou ◽  
Alarich Weiss
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Temperature Dependence ◽  
Room Temperature ◽  
Unit Cell ◽  
Space Group ◽  
Temperature Range ◽  
Temperature Coefficients ◽  
Group D

AbstractThe two line 35Cl NQR spectrum of 4,5-dichloroimidazole was measured in the temperature range 77≦ T/K ≦ 389. The temperature dependence of the NQR frequencies conforms with the Bayer model and no phase transition is indicated in the curves v ( 35Cl)= f(T). Also the temperature coefficients of the 35Cl NQR frequencies are "normal". At 77 K the 35Cl NQR frequencies are 37.409 MHz and 36.172 MHz and at 389 K 35.758 MHz and 34.565 MHz. The compound crystallizes at room temperature with the tetragonal space group D44-P41212, Z = 8 molecules per unit cell; at 295 K : a = 684.2(5) pm, c = 2414.0(20) pm. The relations between the crystal structure and the NQR spectrum are discussed.

NQR, NMR, and X-ray crystal structure studies of [4-C2H5-C6H4NH3]2MBr4 (M=Zn, Cd)

2018 ◽  
Vol 73 (9) ◽  
pp. 611-616
Author(s):  
Hideta Ishihara ◽  
Hisashi Honda ◽  
Ingrid Svoboda ◽  
Hartmut Fuess
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Temperature Dependence ◽  
Benzene Ring ◽  
Structural Phase Transition ◽  
Structural Phase ◽  
Unit Cell ◽  
Organic Layers ◽  
Nuclear Magnetic Resonance Spectra ◽  
Quadrupole Resonance

AbstractThe crystal structure of [4-C2H5-C6H4NH3]2ZnBr4 (1) has been determined at 150(2) K: triclinic, P1̅, a=724.82(2), b=1194.20(4), c=1322.26(4) pm, α=74.151(3), β=80.887(3), γ=80.434(3)°, and Z=2. There are two crystallographically independent cations in the unit cell of 1: one has its benzene ring perpendicular to the crystallographic a axis of the unit cell and the other one has its benzene ring perpendicular to the c axis. These cations are alternatingly located along the c axis and form organic layers, and the ZnBr4 anions form inorganic layers in between. Zn–Br···H–N hydrogen bonds are formed between cations and anions. In accordance with the crystal structure, four nuclear quadrupole resonance (NQR) lines of 81Br were observed. The temperature dependence of the 81Br NQR frequencies between 77 and 320 K shows a peculiar feature which is not due to a structural phase transition. The measurement of 13C nuclear magnetic resonance spectra at around T=340 K indicates a redistribution of cations. The temperature dependence of 81Br NQR frequencies and differential thermal analysis measurements show that [4-C2H5-C6H4NH3]2CdBr4 (2) undergoes a structural phase transition at around 190 K.

Primäre und sekundäre Ethyl-und i-Propylsulfoniumsalze sowie Kristallstruktur von i-C3H7SH2+SbF6- [1]

1996 ◽  
Vol 51 (2) ◽  
pp. 277-285
Author(s):  
Rolf Minkwitz ◽  
Ulrike Lohmann ◽  
Hans Preut
Keyword(s):  
Crystal Structure ◽  
Structure Analysis ◽  
Bond Distance ◽  
Crystal Structure Analysis ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
Spectroscopic Methods ◽  
Sulfonium Salt ◽  
Space Group

Abstract The synthesis of salts of the type RnSH3-n+MF6- (R = C2H5, i-C3H7; n = 1, 2; M = As, Sb) by protonation of the corresponding thiols and sulfides in the superacid systems HF/MF5 is reported. The salts have been characterized by vibrational and NMR spectroscopic methods. Isopropylsulfonium hexafluoroantimonate is the first known example of a sulfonium salt, for which a SH bond distance has been determined by a crystal structure analysis, i-C3H7SH2+SbF6- crystallizes in the monoclinic space group P21/m with a = 568.0(4), b = 801.1(6), c = 1019.7(8) pm, β = 82.63(6) °, with two formula units per unit cell.

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