Zeitschrift fur Kristallographie - Crystalline Materials
2194-4946
2196-7105
Đức
Cơ quản chủ quản: Walter de Gruyter GmbH , de Gruyter
Lĩnh vực:
Inorganic ChemistryMaterials Science (miscellaneous)Condensed Matter Physics
Các bài báo tiêu biểu
First principles methods using CASTEP Abstract
The CASTEP code for first principles electronic structure calculations will be described. A brief, non-technical overview will be given and some of the features and capabilities highlighted. Some features which are unique to CASTEP will be described and near-future development plans outlined.
Tập 220 Số 5-6 - Trang 567-570 - 2005
CRYSTAL: a computational tool for the <i>ab initio</i> study of the electronic properties of crystals Abstract
CRYSTAL [1] computes the electronic structure and properties of periodic systems (crystals, surfaces, polymers) within Hartree-Fock [2], Density Functional and various hybrid approximations.
CRYSTAL was developed during nearly 30 years (since 1976) [3] by researchers of the Theoretical Chemistry Group in Torino (Italy), and the Computational Materials Science group in CLRC (Daresbury, UK), with important contributions from visiting researchers, as documented by the main authors list and the bibliography.
The basic features of the program CRYSTAL are presented, with two examples of application in the field of crystallography [4, 5].
Tập 220 Số 5-6 - Trang 571-573 - 2005
Mathematische Theorie der Regelung nach der Korngestah bei affiner Deformation
Tập 81 Số 1-6 - Trang 285-297 - 1932
Refinement of the Fe<sub>4</sub>Al<sub>13</sub> structure and its relationship to the quasihomological homeotypical structures Abstract
The crystal structure of Fe4 Al13 was refined using single crystal diffractometer data: Pearson symbol mC102, space group C 2/m ; a = 15.492(2) Å, b = 8.078(2) Å, c = 12.471(1) Å, β = 107.69(1)°; RF
= 0.053, RF
(w ) = 0.044 for 1127 reflections and 137 refined parameters. The coordination numbers of atoms are 9, 10. 11 for iron and 10, 12, 13, 14 for aluminium. The shortest interatomic distances are: Fe–Fe – 2.902 Å, Fe–Al – 2.374 Å, Al–Al – 2.533 Å. A preferred occupation of pentagonal prismatic coordinated positions by aluminium was found. The structural relationship between the Fe4 Al13 structure and chemically homologous and homeotypical structures of aluminium and gallium containing systems with the 3d transition metals is discussed. The greatest similarity was found concerning the coordination polyhedra, especially that of transition metal atoms. The main common feature of these homeotypical structures is the presence of pentagonal “channels”, which is strongly dependent on the chemical composition. With increasing atomic number of the 3d transition metal, the stability range of these structures shifts to the transition metal-rich concentration. It is concluded that there is a connection between the occurrence of aluminium and gallium-containing decagonal and icosahedral phases and the existence of the infinite one-dimensional pentagonal channels in the intermetallic compounds showing a similar chemical composition.
Tập 209 Số 6 - Trang 479-487 - 1994
Clinoptilolite: the distribution of potassium atoms and its role in thermal stability Abstract
The crystal structure of clinoptilolite has been worked out, based on C2/m , using two crystals from two different localities: one from Kuruma Pass, Japan, a = 17.660(4) Å, b = 17.963(5) Å, c = 7.400(3) Å, β = 116.47(3)°, and the other from Agoura, U. S. A., a = 17.662(4) Å, b = 17.911(5) Å, c = 7.407(3) Å, β = 116.40(3)°. In the tetrahedral framework of the heulandite type there are recognized four kinds of main cation positions, M(l), M(2), M(3), and M(4). At M(l) and M(2), which have so far been known as cation positions in the heulandite structure, Na and C'a are located ; M(l) tends to accommodate more Na than M(2). The new position, M(3), which is specific for K, is located almost at the center of the eight-membered ring of the channel parallel to a . This position is coordinated by six framework oxygen atoms and three water molecules. At M(4), which is octahedrally coordinated by six water molecules, Mg is located. It is very likely that these four positions are characteristic of all members of the heulandite-group zeolites. The difference between clinoptilolite and heulandite is primarily in the difference of site content: for clinoptilolite, M(l) and M(2) are rich in Na, while for heulandite, they are rich in Ca. The occupancy of K at M(3) in clinoptilolite is, in general, higher than that of heulandite. The location and coordination of K explain the evidence that the presence of K in the structure is one of the controlling factors of the thermal behaviour of the heulandite-group zeolites.
Tập 145 Số 3-4 - Trang 216-239 - 1977
The role of OH and H<sub>2</sub>O in oxide and oxysalt minerals Abstract
Hydrogen plays an extremely important role in the structure and chemistry of the oxide and oxysalt minerals. The characteristics of this role can be profitably analyzed in a simple and intuitive fashion using bond-valence theory. For any crystal structure, the structural unit may be defined as the strongly bonded part of the structure; structural units are linked together by interstitial species , usually alkali or alkaline earth cations and (H2 O)0 groups that are involved in much weaker bonding. This scheme gives a binary representation of even the most complex structure. The interaction between the structural unit and the interstitial species can be quantitatively evaluated using the valence-matching principle (Brown, 1981).
As components of the structural unit, (OH)− and (H2 O)0 play a major role in dictating the dimensional polymerization of the structural unit because of the very asymmetric nature of the donor-hydrogen and hydrogen…acceptor interactions. As an interstitial component, (H2 O)0 can play three different roles. Interstitial (H2 O)0 may bond to an interstitial cation, essentially forming a complex cation . In this role, (H2 O)0 acts as a bond-valence transformer, moderating the Lewis acidity of the interstitial cations such that it matches the Lewis basicity of the structural unit and the valence-matching principle is satisfied. Interstitial (H2 O)0 need not bond to an interstitial cation to occupy well-ordered atomic positions; a stable hydrogen-bonded network can occur in the interstitial regions between structural units. The role of such (H2 O)0 is to satisfy the bond-valence requirements of H atoms that are part of the structural unit, propagating the bonding across the interstitial space to other parts of the structural unit. Occluded (H2 O)0 may occur in some minerals. Such (H2 O)0 is not bonded to interstitial cations and does not participate in a static ordered hydrogen-bond network. However, this type of (H2 O)0 will still affect many of the physical properties of a mineral.
Tập 201 Số 3-4 - Trang 183-206 - 1992
The Crystal Structure of TlSe, Thallous Thallic or Thallosic Selenide
Tập 101 Số 1-6 - Trang 396-405 - 1939
The crystal structure of the binary iridium-aluminum IrAl<sub>2.75</sub> and rhodium-aluminum RhAl<sub>2.63</sub> phase Abstract
The crystal structures of IrAl2.75 (“Ir2 Al5 ”) and RhAl2.63 (“Rh2 Al5 ”) phases have been studied with single crystal methods: space group P 23, IrAl2.75 , a = 7.674(1) Å, Z = 8, RF
= 0.053 (457 hkl , 29 parameters) and RhAl2.63 , a = 7.6692(1) Å, RF
= 0.042 (684 hkl , 29 parameters). The unit cell contains three transition metal sites and five aluminum sites. Most aluminum sites reveal strong defects in the occupations, some of them are described as being split. The overall number of atoms in the unit cell is 30(1) for IrAl2.75 and 29.0(3) for RhAl2.63 . Ordering and full occupation lead either to the AuZn3 (space group Pm [unk]n ) or to the hypothetical “Ir4 Al13 ” structure (space group Pm [unk]).
Tập 212 Số 6 - Trang 439-444 - 1997
High-pressure crystal chemistry of binary intermetallic compounds Abstract
Effects of high pressure on intermetallic compounds are reviewed with regards to structural stability and phase transitions. Changes of bonding properties and electronic structure are examplified by means of the elemental metals caesium and titanium, the latter forming an internal intermetallic compound at high pressures. After a short systematic overview regarding pressure effects, structural transformations in selected classes of intermetallic compounds like Zintl phases and AlB2 -type arrangements precedes sections concerning high-pressure synthesis of Laves phases and intermetallic clathrates.
Tập 221 Số 5-7 - Trang 420-434 - 2006