bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystallographic point and space group symmetries in the one-and two-body density of crystals and generalized Patterson functions: Fourier path integral Monte Carlo case studies of novel high-temperature/high-pressure4He quantum crystals
Authors: Gernoth Klaus A.
Published: December 2003

We present a complete formal analysis of crystallographic point and space group symmetries in the local one- and two-body densityρ(x) andρ2(x1,x2) of crystals and from there develop the mathematical theory of generalized Patterson functions. The two-body densityρ2(x1,x2) andρ(x1)ρ(x2) may be written as symmetrized lattice Fourier series over all reciprocal lattice vectorsKwith Fourier transforms that are functions of the relative vectorr=x1–x2. In the new formalism derived here the usual Patterson function turns out to be the lowest-lyingK= 0 lattice Fourier transform in the Fourier series representation of the uncorrelated productρ(x1)ρ(x2) of one-body densities. All otherK≠ 0 Fourier transforms in the Fourier series ofρ(x1)ρ(x2) may be regarded as generalized Patterson functions. In complete analogy to these generalized Patterson functions the Fourier transform functions in the Fourier series of the fully correlated two-body densityρ2(x1,x2) may be regarded asK= 0 andK≠ 0 fully correlated generalized Patterson functions. It is shown that the former generalized Patterson functions represent the uncorrelated long-range limits for large interparticle distances of the latter, fully correlated, generalized Patterson functions. Both types of generalized Patterson functions may be cast in the form of symmetry-adapted trigonometric series with expansion functions that depend on the relative distancer= |r| and on the polar angle ofr. The symmetrized trigonometric series representations of the generalized Patterson functions are given here explicitly in specific applications of the new formalism to crystallographic space groupP63/mmc. In exact path integral Monte Carlo case studies of novel high-temperature/high-pressure4He quantum crystals in the hexagonal close-packed structure we present and discuss exact numerical results for the one-body densityρ(x) and for expansion functions, for both types of generalized Patterson functions, in the symmetrized trigonometric series representations of the generalized Patterson functions. The numerical results for the two types of generalized Patterson functions are compared to each other.
In situandex situinvestigation of the displacive phase transformations Ag3Sn(h) → Ag3Sn(l) and Ag3Sb(h) → Ag3Sb(l)
Authors: Ellner M. , Mittemeijer E. J.
Published: December 2003

The occurence of the polymorpic phase transformations Ag3Sn(h) → Ag3Sn(l) and Ag3Sb(h) → Ag3Sb(l) was demostratedin situprimarily by means of high-temperature X-ray powder diffracion and thermal analysis as well as byex situX-ray powder diffraction. Both solid- and liquid-quenched aloys were investigated. The structure of the high-temperature phases Ag3Sn(h) and Ag3Sb(h) is isotypic with Mg (Pearson symbolhP2, space groupP63/mmc); unit cell parameters are:a= 2.9863(8) Å,c= 4.784(2) Å for Ag3Sn(h) anda= 2.9944(9) Å,c= 4.812(3) Å for Ag3Sb(h). The low temperature phases Ag3Sn(l) and Ag3Sb(l) are orthorhombic displacive homeotypes of the hexagonal close-packed structure, isotypic with withβ-TiCu (oC4,Cmcm). The unit cell parameters are for Ag3Sn(l):a= 2.9973(5) Å,b= 5.1618(8) Å,c= 4.786(1) Å,b/a= 1.722 < √3; and for Ag3Sb(l):a= 2.9947(3) Å,b= 5.2497(5) Å,c= 4.8495(7) Å,b/a= 1.753 > √3. The crystal structures and the phase transformations werde discussed in terms of the valence electron concentration.
Geometrical isomerism in uranyl chromates II. Crystal structures of Mg2[(UO2)3(CrO4)5](H2O)17 and Ca2[(UO2)3(CrO4)5](H2O)19
Authors: Krivovichev Sergey V. , Burns Peter C.
Published: December 2003

Geometrical isomerism of uranyl chromate sheets occurs in the structures of Mg2[(UO2)3(CrO4)5](H2O)17 and Ca2[(UO2)3(CrO4)5](H2O)19. Both compounds were prepared by evaporation from aqueous solutions. Compound 1 is orthorhombic, Pbca, a = 19.9206(10), b = 21.0526(10), c = 18.4966(9) Å, V = 7757.1(7) Å3; R
1 = 0.050 for 6332 unique reflections with |F
o| ≥ 4σF
. Compound 2 is monoclinic, P21/m, a = 11.0359(5), b = 17.5364(7), c = 11.5056(5) Å, β = 118.178(1)°, V = 1962.8(2) Å3; R
1 = 0.037 for 6209 unique reflections with |F
o| = 4σ
F. Both structures contain sheets of composition [(UO2)3(CrO4)5] involving corner-sharing UO7 pentagonal bipyramids and CrO4 tetrahedra. The sheets are parallel to (100) in both structures. Mg2+ and Ca2+ cations are coordinated by H2O molecules and are located in the interlayer. The topology of the [(UO2)3(CrO4)5] sheets in both structures is the same, whereas their geometrical structures are different, and they are geometrical isomers. The sheets differ in the orientations of non-shared corners of chromate tetrahedra relative to the plane of the sheet. In order to describe the geometrical structure of the isomers, the concept of orientation matrix of tetrahedra is introduced. It has been shown that there are at least three geometrical isomers of the [(UO2)3(CrO4)5] sheet in uranyl chromates that differ in their orientation matrices of the tetrahedra.
Dimorphism in mercury(II) tellurite(IV) tellurate(VI): preparation and crystal structures of α- and β-Hg2Te2O7
Authors: Weil Matthias
Published: December 2003

The mixed-valent mercury(II) tellurite(IV) tellurate(VI), Hg2Te2O7, is dimorphous and crystallizes in two modifications with slightly different density, named α-(high density) and β-(low density). Colourless single crystals of both modifications were prepared simultaneously by chemical transport reactions, starting from stoichiometric mixtures of HgO, TeO2 and TeO3 in sealed and evacuated silica glass ampoules. A temperature gradient of 600 → 550°C was applied and small amounts of HgCl2 served as transport agent. The crystal structures (α-Hg2Te2O7: C2/c, Z = 8, a = 12.910(4), b = 7.407(2), c = 13.256(4) Å, β = 112.044(5)°, 1711 structure factors, 73 parameters, R[F
2 > 2σ(F
2)] = 0.0325, wR(F
2 all) = 0.0796; β-Hg2Te2O7: Aea2, Z = 16, a = 7.4405(12), b = 23.713(4), c = 13.522(2) Å, 3528 structure factors, 132 parameters, R[F
2 > 2σ(F
2)] = 0.0430, wR(F
2 all) = 0.0738) are not directly correlated by a supergroup-subgroup relation but show similar building units which are also found in the structure of the mixed-valent Te(IV,VI) compound BaCuTe2O7. Characteristic structural feature of both polymorphs is a slightly distorted hexagonal array made up of isolated 1
∞[TeVIO4/1O2/2] chains running parallel to [010] for the α- and to [100] for the β-modification. The chains are interconnected via [TeIVO4] polyhedra to form infinite Te2O7
4- layers with a different topology for both structures. In α-Hg2Te2O7 the layers are linearly ordered and spread parallel to (101̅) whereas in β-Hg2Te2O7 the zig-zag arranged layers extend parallel to (001). The lone-pairs of the TeIV atoms are stereochemically active and protrude into the cavities of the structure. For both structure types the mercury atoms are situated in-between the anionic sheets and interconnect the layers into the three-dimensional network. The coordination numbers of the mercury atoms range from 6–8 in both modifications with the typical Hg–O distances between 2.03–3.0 Å.
(Na-15-Krone-5)2ReCl6·4 CH2Cl2, eine Struktur mit CH2Cl2-Molekülen in pseudohexagonalen Kanälen
Authors: Müller Ulrich , Noll Andrea
Published: December 2003

The monoclinic crystal structure of (Na-15-crown-5)2ReCl6·4 CH2Cl2 was determined by X-ray diffraction (P21/c, Z = 4, R
1 = 0.061). It contains octahedral ReCl6
2- ions that are joined on two opposite octahedron faces to two Na+ ions; each Na+ is coordinated with one crown ether molecule. One of the crown ether molecules is disordered in two orientations. The resulting ‘Kro-Re-Kro’ units have a nearly cylindrical shape and are stacked to rods that run parallel to c. The rods form a pseudohexagonal rod packing in which one third of the rods is missing. The channels in the places of the missing rods are filled with solvent molecules showing high thermal motion. Another description is that of a hexagonal-closest packing of Kro-Re-Kro units, the channels resulting from the strings of face-sharing octahedral voids of the packing. Group–subgroup relations show that the deviation of the Kro-Re-Kro packing from hexagonal symmetry is astonishingly small. The crystal structure of ‘(P(C6H5)4)2ReCl6·2 CH3CN’ is confirmed; however, the chemical formula must be corrected, it is (P(C6H5)4)2ReCl6·4 CH3CN).
X-ray study of the pseudopolymorphism of the azithromycin monohydrate
Authors: Montejo-Bernardo J. M. , García-Grande Santiago , Bayod-Jasanada M. S. , Lavona-Díaz L. , Llorente I.
Published: December 2003

A combination of X-ray powder diffraction and single crystal studies on azithomycin pseudopolymorphs give the precise solid state composition of all monohydrate pseudopolymorphs reported. According to the X-ray results the four monohydrates of azithromycin studied have the same crystallographic parameters. Furthermore, the analysis of the relative intensities from the powder patterns points to very similar chemical compositions and crystal structures. This result has been confirmed by the single crystal studies. The single crystal studies show that the solid state conformation of the azithromycin molecules is affected by the presence of solvents. The solvent methanol molecules were found disordered probably due to the existence of many positions where the hydrogen bonding is favoured and the large size of the available space to host the solvents.
Hydrogen in novel solid-state metal hydrides
Authors: Yvon K.
Published: December 2003

Solid-state metal hydrides display hydrogen densities close to that of liquid hydrogen and thus provide a safe and efficient way of storing hydrogen. As a result of recent neutron and synchrotron diffraction work some novel metal hydrides have been characterized that shed new light on the nature of metal-hydrogen interactions. While hydrogen appears as an anion surrounded by a large inventory of cation configurations in ionic hydrides such as Ca4Mg3H14, Ca19Mg8H54, Eu2MgD6, Eu6Mg7D26 and Eu2Mg3D10, it acts as a terminal ligand in covalently bonded hydride complexes based on p-elements such as [BH4]– and d-elements such as [IrH5]4– and [IrH4]5– in the complex hydrides LiBH4 and Mg6Ir2H11, respectively. Surprisingly, hydride complexes and hydride anions can also be discerned in typically metallic (interstitial) hydrides such as NdMgNi4H4 (= Nd3+Mg+2·[Ni4H4]5–) and LaMg2NiD7 (= La3+Mg+2
2·[NiH4]4–·3H–). Some hydrides also reveal other interesting features such as a hydrogenation induced Ce4+ → Ce3+ valence change in CeMn1.8Al0.2H4.4 at room temperature that is accompanied by a Mn/Al metal atom exchange over distances of ~2.6 Å, and a hydrogen induced metal-to-nonmetal transition near ambient conditions that leads from the metallic compound Mg3Ir to the red colored hydride Mg6Ir2H11. In this article recent work and some methodological aspects are highlighted.
Recrystallisation of HDA ice under pressure by in-situ neutron diffraction to 3.9 GPa
Authors: Klotz S. , Hamel G. , Loveday J. S. , Nelmes R. J. , Guthrie M.
Published: December 2003

We have studied by in-situ neutron diffraction the recrystallisation behaviour of HDA ice in the pressure range 0.3–3.9 GPa, i.e. the entire stability range of HDA. We report quantitative and detailed structural information on the various high pressure ice phases formed metastably at low temperatures. We find that between ~0.4–0.7 GPa, HDA transforms at 175 K to mainly phases IV and V, and XII, and at 1–1.2 GPa to a mixture of ice VI and XII. On isothermal compression at 100 K, HDA recrystallises to an ice VII-like structure which is either partially ordered or mixed with ice VIII. Full structural data obtained by Rietveld refinements are reported for all these phases at low temperatures. Phases IV, V and XII are fully hydrogen disordered when obtained from HDA. The transformation behaviour in the 0.5–1.2 GPa range is in good agreement with the picture reported from quenched-recovered samples, although some differences persist in the recrystallisation to IV/XII mixtures. The recrystallisation behaviour of HDA over the entire pressure range appears to follow closely that of liquid water under pressure.
The determination of anharmonic probability densities from static and dynamic disorder by neutron powder diffraction
Authors: Boysen H.
Published: December 2003

Atomic probability densities as derived from a careful analysis of the Debye-Waller factors contain important information about the average static and dynamic disorder in crystals. Although the inclusion of anharmonic terms often requires single crystal data, in favourable cases, in particular at high temperatures, it is possible or even necessary to rely on neutron powder experiments too. This is illustrated by several examples including the anharmonic motion of the atoms in ZnS, the anionic diffusion and the static disorder in zirconia based super-ionic conductors, and the critical behaviour at the structural phase transition in PbTiO3. Anharmonic and split models are compared on the example of Zr—Mg—O—N.
Structural analysis of complex materials using the atomic pair distribution function — a practical guide
Authors: Proffen Th. , Billinge S. J. L. , Egami T. , Louca D.
Published: December 2003

Modern materials and their properties are often characterized by varying degrees of disorder. Routine crystallographic structure solution only reveals the average structure. The study of Bragg and diffuse scattering yields the local atomic arrangements holding the key to understanding increasingly complex materials. In this paper we review the pair distribution function technique used to unravel the local structure. We aim to give a practical overview and make this method easily accessible to the wider scientific community.
Stroboscopic neutron diffraction from spatially modulated systems
Authors: Eckold G. , Gibhardt H. , Caspary D. , Elter P. , Elisbihani K.
Published: December 2003

The combination of stroboscopic techniques and neutron diffraction can be used to study the kinetics of structural changes in condensed matter on a microscopic level. Transient states may be identified and characterized on time-scales down to the microsecond regime. Hence, valuable information about the underlying mechanisms can be obtained from time-resolved experiments. Particularly interesting subjects for this type of investigation are spatially modulated systems which undergo phase transitions or phase separation. The potential of stroboscopic neutron diffraction is demonstrated using three different examples in which samples are periodically perturbed by the variation of temperature, mechanical stress or electric field and their structural response is characterized by time-resolved diffraction. Spinodal decomposition in ionic crystals of the silver-alkali halide type is shown to be dominated by two different processes on different time-scales. The stress-induced phase transition into the incommensurate phase of quartz involves relaxation processes which are reflected by different kinetic behaviours of Bragg peaks and satellite reflections, respectively. Finally, metastable transient states are observed during the field induced lock-in transition in ferroelectric Rb2ZnCl4which are most probably due to strain fields and pinning effects.
Single-crystal neutron diffractometry — Recent developments and trends
Authors: Graf H. A.
Published: December 2003

An overview is given over recent developments and trends in single-crystal neutron diffractometry. Special emphasis is put on instrumental developments which have considerably enhanced the efficiency of neutron scattering experiments over the last years by improving monochromator and/or detector systems. Not discussed are developments in the field of polarised neutrons. Examples from the Berlin Neutron Scattering Center (BENSC) are given for the measurement of short-range magnetic order using the flat-cone diffractometer E2 of BENSC and of the study of long-range magnetic order making use of a high-field cryomagnet at BENSC. The perspectives of neutron diffractometry within the next 5 to 10 years are discussed with view on the new powerful spallation sources SNS (under construction in the United States), JSNS (under construction in Japan) and ESS, the European Spallation Source, planned to be constructed in Europe.
A review of sample environments in neutron scattering
Authors: Bailey I. F.
Published: December 2003

Sample environment equipment, cryostats, furnaces, pressure cells etc. are an essential adjunct to most neutron scattering experiments to induce the sample being studied into a phase or state of particular interest. He we give a brief overview of the diverse range of Sample Environment equipment that is currently in use, a background to its development and also some recent trends.
High resolution neutron protein crystallography. Hydrogen and hydration in proteins
Authors: Niimura N. , Chatake T. , Ostermann A. , Kurihara K. , Tanaka I.
Published: December 2003

Neutron diffraction provides an experimental method of directly locating hydrogen atoms in proteins, and the development of the neutron imaging plate (NIP) became a breakthrough event in neutron protein crystallography. The general features of the NIP are reviewed. A high resolution neutron diffractometer dedicated to biological macromolecules (BIX-3) with the NIP has been constructed at Japan Atomic Energy Research Institute and this has enabled 1.5 Å resolution structural analyses of several proteins to be carried out. The specifications of BIX-3 and LADI (a quasi-Laue type diffractometer installed in the Institut Laue-Langevin) are compared. The crystal structures of myoglobin, wild type rubredoxin and a mutant of rubredoxin have been carried out using BIX-3. From these studies, several topics, such as the location of hydrogen bonds and certain acidic hydrogen atoms, the identification of methyl hydrogen atoms, details of H/D exchange and dynamical behavior of hydration structures have been investigated, and important information has been extracted from the structural results. Finally, a systematic procedure to grow large single crystals of proteins or nucleic acids is described.
Chemical, thermal, and theoretical analysis of the α—β phase transition of Ba3Tt4 compounds
Authors: Zürcher F. , Leoni S. , Nesper R.
Published: December 2003

The α to β phase transition of Ba3Tt4 (Tt = Si, Ge; Ba3Ge4 and Ba3Si4 structure type, respectively) has been investigated experimentally by differential thermal analysis (transition temperature 628 K) and variation of the composition Ba3Si
x
Ge4–

x
which shows that the transition is clearly dependent on the compositional parameter (0.4 ≤ x ≤ 0.5). The five new Zintl compounds Ba3Si1.89Ge2.11, Ba3Si1.05Ge2.95, Ba3Si0.57Ge3.43 (Ba3Si4 structure type) and Ba3Si0.31Ge3.69, Ba3Si0.16Ge3.84 (Ba3Ge4 structure type) were synthesized and structurally characterized. We have also developed a topological model for the description of the phase transition which is based on the Periodic Nodal Surface (PNS) approach.
Geminography — The science of twinning applied to the early-stage derivation of non-merohedric twin laws
Authors: Nespolo Massimo , Ferraris G.
Published: December 2003

The recognition of twinning and the determination of the twin laws are nowadays often entrusted to "black-box" software packages. This approach may be both risky and uneconomical. It is risky because never a procedure should be blindly applied. It is uneconomical if procrastinates the analysis of twinning at the very late stage of structure solution and refinement, whereas in many cases this analysis can and should be applied much earlier. In this paper we present a brief survey of the working strategies to be applied to the structural study of twinned crystals, emphasizing the role of the crystallographer, rather than that of the machine.
Pentagonal and trigonal quasilattices and their approximants
Authors: Subramaniam Anandh , Lord E. A.
Published: December 2003

The Strip Projection Method is used to generate pentagonal and trigonal 2-dimensional quasilattices as rational approximants to the icosahedral quasilattice. Further, 3-dimensionally periodic structures are generated as rational approximants to these 2-dimensional quasilattices. A simplified approach based on uniform distortions of perpendicular space is put forth for the analyses.
Thermal expansion of lattice parameters of La3Nb0.5Ga5.5O14, La3Ta0.5Ga5.5O14 and La3SbZn3Ge2O14
Authors: Pavlovska A. , Schneider J. , Werner S. , Maximov B. , Mill B. , Baetz C.
Published: December 2003

The thermal expansion of trigonal La3Nb0.5Ga5.5O14 (LNG), La3Ta0.5Ga5.5O14 (LTG) and monoclinic La3SbZn3Ge2O14 (LSZG) was studied with X-ray powder diffraction technique. The trigonal crystal structures of LNG and LTG are stable under elevated temperature and no phase transition was detected up to 1123 K, whereas the monoclinic LSZG undergoes a phase transition at temperature 523(50) K, presumably to trigonal space group P321. The thermal expansion of LNG, LTG and LSZG is anisotropic. This can be explained by the layer structure of title compounds. The mean coefficients in the monoclinic a, b and c directions for LSZG from room temperature to 523(50) K are 8.20, 8.47 and 6.22 [10-6/K], respectively. The mean coefficients in the trigonal a and c directions are 8.141 and 6.162 [10-6/K] for LNG; 7.653 and 5.344 [10-6/K] for LTG from room temperature to 1123 K.
A neutron diffraction study of quartz-type FePO4: high-temperature behavior and α–β phase transition
Authors: Haines J. , Cambon O. , Hull S.
Published: December 2003

The structural evolution of quartz-type iron phosphate, FePO4, was studied by time-of-flight neutron powder diffraction from 294 K up to 1073 K. The refined structural parameters of the low-temperature α phase tend towards the values obtained for high-temperature β-quartz-type FePO4. In particular, the Fe—O—P bridging angles increase and the tetrahedral tilt angles decrease strongly as the α–β phase transition at 980 K is approached. Important discontinuities in these structural parameters are observed at this first-order transition. Thermal expansion in the α phase is strongly non-linear and dominated by these angular variations. There is essentially no thermal expansion in the β phase due to the absence of these mechanisms. The behavior in the α phase is distinct from those of other α-quartz homeotypes in that the angular variations are greater than for the other materials, including SiO2 and AlPO4, and do not scale with the initial structural distortion. This may be an indication of a dynamic instability in α-quartz-type FePO4.
The pyroxene-spinel polysomatic system
Authors: Zvyagin Boris B. , Merlino St.
Published: December 2003

Modules 〈P〉 and 〈S〉 which taken separetely constitute the structures of pyroxene and spinel respectively, may give rise, in combination, to a wide polysomatic system ranging between these two minerals as end members. The system is firstly discussed on the basis of complex layers 〈PmSnPm〉, built up by somatic parts of both spinel and pyroxene, from the 〈(P/2)S(P/2)〉 modules, which are the OD layers giving rise to the sapphirine family, to the general 〈Pm/2SnPm/2〉, which includes 〈(P/2)Sn(P/2)〉 (characterizing the structure of calcium aluminium ferrite and SFCA-I compound) and 〈PSP〉 (characterizing the surinamite-type structures). Afterwards the system is discussed on the basis of 〈Pm〉 and 〈Sn〉 layers, with derivation of a new polytypic family closely related to that of sapphirine. Finally the possible stacking sequences of single modules 〈S〉, giving rise to the spinelloid series and the stacking and condensation of single 〈P〉 modules, giving rise to the whole biopyriboles series, are presented and discussed.
9,10 Phenanthrenequinone, not your average structure
Authors: Rae A. David , Willis A. C.
Published: December 2003

9,10-phenanthrenequinone, C14H8O2, is both polymorphic and polytypic. The β form can have different symmetries arising from different stackings of ordered layers perpendicular to c
p*. These structure options are best understood using occupancy wave modulations of a 1 : 1 disordered parent structure in space group P21/c. The disorder is resolved by having ordered layers of C1̅ symmetry in a cell with a = 2a
p, b = 2b
p. Ordering the stacking sequence allows two orientations of a Z = 8, Cc, c = c
p structure and two orientations of a Z = 16, F1̅, c = 2c
p structure. It was found that for some crystals it is necessary to model the reflection data assuming uncorrelated mosaic blocks of different space group symmetry as well as orientation. Reliable geometry for both the Cc and F1̅ components were then obtained. Likewise, the α form can be described as arising from a 1 : 1 disordered parent structure in space group Pnmn where the disorder is resolved by having ordered layers of P2/c symmetry perpendicular to a
p* in a cell with b = b
p, c = 2c
p. Ordering the stacking sequence allows two orientations of a Z = 4, P21
cn structure with a = a
p and two orientations of a Z = 8, B2/c structure with a = 2a
p (a non standard setting of P2/c).
A comparative study of pressure-induced lattice strain of α- and γ-polymorphs of glycine
Authors: Boldyreva E. V. , Ahsbahs H. , Weber H.-P.
Published: December 2003

The effect of hydrostatic pressure up to 4 GPa on the two polymorphs of glycine α — s.g. P21/n, and γ — s.g. P31 (P32)) was studied by X-ray powder diffraction using a synchrotron radiation source (λ = 0.7 Å, a MAR345 image plate detector). No polymorphic transformations were detected. Relative volume changes and the aniso tropy of structural distortion of the two polymorphs were compared. The directions of maximum and minimum lattice strain were related to the directions of weak and strong hydrogen bonds in the structures.
Correlations, convolutions and the validity of electron crystallography
Authors: Dorset Douglas L.
Published: December 2003

Although often an object of controversy, electron crystallography has emerged as a useful technique for characterization of the microcrystalline state, capable of elucidating crystal structures of unknown substances. Despite the complicated multiple scattering perturbations to diffracted intensities, experimental conditions can be adjusted to favor data collection where the experimental Patterson function still resembles the autocorrelation function of the actual crystal structure. Satisfying this condition is often sufficient to permit structure solution from such data by direct methods. While the application to organic structures may seem obvious, there are surprising successes with data sets from inorganic materials. The account given in this paper, in part, portrays work leading to the A. L. Patterson Award to the author from the American Crystallographic Association.
The quantitative analysis of electrostatic potential and study of chemical bonding by electron diffraction structure analysis
Authors: Avilov A. S.
Published: December 2003

The development of the electron diffractometry methods jointly the analytical methods of electrostatic potential (ESP) reconstruction and its topological analysis allowd one to proceed to the quality new level of electron diffraction structure analysis (EDSA): investigation inner crystalline electrostatic field, which knowledge permitts to study the relation of the atomic structure with physical properties of crystals. The review of the last achivements in this direction, obtained in the Institute of Crystallography of Russian Academy of Sciences, in which EDSA method was discovered, is done. The possibility of the EDSA method to solve precise problems of quantitative analysis of the electrostatic potential is shown on the examples of investigations of the ESP distributions and chemical bonding in crystals with NaCl-type structure and covalent crystal Ge. It is also shown that quantitative data on the potential distribution considerably enlarge conceptions on the nature of interatomic and inetrmolecular interactions in crystals.
Electron crystallography on polymorphic organics
Authors: Kolb U. , Matveeva G. N.
Published: December 2003

Organic materials, such as non-linear optical active compounds (1-(2-furyl)-3-(4-aminophenyl)-2-propene-1-one (FBAPPO) and 1-(2-furyl)-3-(4-benzamidophenyl)-2-propene-1-one (FAPPO)), polymeric materials like the metal coordinated polyelectrolyte (Fe(II) [ditopic bis-terpyridin] (MEPE)) or polymorphic materials (e.g. Cu-phthalocyanine), which do not crystallize big enough for single crystal x-ray structure analysis have been investigated by electron diffraction (ED) at 100 and 300 kV acceleration voltage. Sample preparation (direct crystallization, ultra sonication, ultra microtomy), diffraction strategies (selected area diffraction, nano diffraction, use of double-tilt rotation holder), data collection and data processing as well as structure solution strategies have been chosen dependent on the different requirements of the compounds under investigation. Structure analysis was carried out by simulation usingab initioquantum-mechanical methods like density functional theory (DFT), semi-empirical approach (MNDO/AM1/PM3) and force field packing energy calculations (DREIDING). The structure models resulting from simulation were refined kinematically as rigid bodies. Subsequently, refinements by multi-slice least squares (MSLS) procedures taking dynamical scattering into account were performed. The described combination of different methods which was used successfully on crystallizable materials is also adaptable to insoluble organic materials (e.g. pigments) and polymorphic systems.
Electron diffraction structure analysis: structural research with low-quality diffraction data
Authors: Weirich Th. E.
Published: December 2003

Electron Diffraction Structure Analysis (EDSA) with data from standard selected-area electron diffraction (SAED) is still the method of choice for structure determination of nano-sized single crystals. The recently determined heavy atom structure α-Ti2Se (Albe & Weirich, 2003) is used as an example to illustrate the developed procedure for structure determination from two-dimensionally SAED data via direct methods and kinematical least-squares refinement. Despite the investigated crystallite had a relatively large effective thickness of about 230 Å as determined from dynamical calculations, the obtained structural model from SAED data was found in good agreement with the result from an earlier single crystal X-ray study (Weirich, Pöttgen & Simon, 1996). Arguments, which support the validity of the used quasi-kinematical approach, are given in the text. The influences of dynamical and secondary scattering on the quality of the data and the structure solution are discussed. Moreover, the usefulness of first-principles calculations for verifying the results from EDSA is demonstrated by two examples, whereas one of the structures was unattainable by conventional X-ray diffraction.
Effect of diffraction crystallography on HREM
Authors: Li Fang-hua
Published: December 2003

A simple image contrast theory in high-resolution electron microscopy (HREM) is introduced to demonstrate that below a certain critical crystal thickness the intensity of the Scherzer focus image is linear to the projected potential of an artificial crystal that is isomorphic to the examined one. It has become the theoretical base of electron crystallographic image processing techniques relying on the weak-phase-object approximation and kinematical diffraction. Two techniques of image processing are introduced. One of them aims at determining crystal structures by combining electron diffraction data and applying diffraction analysis methods. To reduce various kinds of electron diffraction intensity distortion the diffraction data are corrected by means of an empirical method set up by referring to the heavy atom method and Wilson statistic. The other one aims at revealing crystal defects at atomic resolution from the image taken with a medium-voltage field-emission high-resolution electron microscope. The dynamical effect is corrected by forcing the integral amplitudes of reflections in the diffractogram of image equal to the amplitudes of corresponding structure factors for the perfect crystal. The principle of the two techniques is briefly introduced, and examples of applications to crystal structure and defect determination are given.
Electron crystallography of aluminum alloy phases
Authors: Gjønnes J. , Hansen V. , Andersen S. J. , Marioara C. D. , Li X. Z.
Published: December 2003

A series of structure analyses during 1994-2001 by electron crystallographic techniques applied to phases in aluminum alloys are reviewed. Methods for structure solution employ electron diffraction intensity data collected by the precession technique, by selected area micro-diffraction and by the convergent-beam technique. High-resolution electron microscope images (HRTEM) are treated by different kind of processing, including exit wave reconstruction. Crystallographic calculations are performed either by direct method or Patterson and Fourier procedures, assuming kinematical scattering, or by refinement from models derived from HRTEM images. Dynamical scattering calculations can be introduced in the refinement stage or as a correction procedure applied to part of the intensity data. The phases studied include primary Al-Fe-(Si) particles, Al-Mn-Si dispersoids, Al-Co quasicrystals and two types of precipitate phases in age-hardening Al-Mg-Si and Al-Zn-Mg alloys.
Visual computing in electron crystallography
Authors: Wan Z. , Liu Y. , Fu Z. , Li Y. , Cheng T. , Li F. , Fan H.
Published: December 2003

VECis a program package forVisual computing inElectronCrystallography. The program is written mainly in C++ and Fortran and is for running underMS Windows95, 98, NT and 2000. Apart from its user-friendly interface, sophisticated text-sensitive online helps and tutorials,VECincludes same unique crystallographic methods. They are direct-method image-processing techniques,ab-initiosolution of incommensurate crystal structures and algorithms for searching one-dimensionally modulated atoms in 4-dimensional Fourier maps. Examples are given in details.
Minerals - a special area of electron diffraction structure analysis
Authors: Zvyagin Boris B. , Zhukhlistov Anatoliy P. , Nickolsky Maxim S.
Published: December 2003

The role of electron diffraction structure analysis in mineralogy is discussed with special reference to developments in the former Soviet Union and the current Russian Federation.
Anomalous thermal expansion behaviour of Na8[AlSiO4]6(NO3)2-sodalite:P4̅3ntoPm3̅nphase transition by untilting and contraction of TO4units
Authors: Rüscher C. H. , Gesing Th.M. , Buhl J.-Ch.
Published: December 2003

X-ray single crystal, X-ray powder and specific heat investigations were carried out on alumosilicate NaNO3-sodalite between 290 K and 1100 K. Single crystal structure determinations at 295 K, 505 K and 720 K reveal the sodalite structure in its partially collapsed form in space groupP4̅3nwhereas at 935 K the z coordinate of the framework oxygen is shifted toz= 0.5 according to an untilted sodalite framework inPm3̅n. The sodium ions are located on 8e(x, x, x) position inP4̅3nand become statistically distributed on 16i(x, x, x) inPm3̅n. The displacements of the nitrate atoms are extraordinarily enlarged at 935 K compared to the values at the lower temperatures. Analysis of the X-ray powder data show a discontinuity in the thermal expansion behaviour atTc= 930 K with the temperature dependence of the lattice parameter described by

acalc=a1—A(Tc—T)0.5,a1=BT+a0

(A= 0:57 pm K–0.5,B= 5:84 · 103pm K–0.5,a0= 909.9 pm,Tin K) which is related to a square root decrease of the volume strain. The anomalous thermal expansion compromises a gradual contraction of TO4units and the disappearence of structural tilt with increasing temperature. The refined data reveal a change of z coordinate of O1 proportional to (Tc-T)1/4inP4̅3nwhich is considered as an effective order parameter in a Landau tricritical description of the phase transition triggered by the displacement of the cage filling ions.
Crystal structure of new hexahydrate dicobalt pyrophosphate Co2P2O7·6H2O: comparison with Co2P2O72H2O, α-, β- and γ-Co2P2O7
Authors: Capitelli F. , Harcharras M. , Assaaoudi H. , Ennaciri A. , Moliterni A. G. G. , Bertolasi V.
Published: December 2003

A new dicobalt pyrophosphate, Co2P2O7·6H2O, has been synthesized and characterized by single crystal X-ray diffraction. The compound belongs to the mono clinic space group P21/n, and its unit cell dimensions are: a = 7.2077(2), b = 18.3373(5), c = 7.6762(2) Å, β = 92.4356(15)°, V = 1013.64(5) Å3, Z = 4. The structural parameters were refined to an R index of 0.0570 for 1937 reflections with I>2σ(I
o). The framework of this pyro phosphate is made by the packing of layers of discrete CoO6 octahedra connected by double tetrahedra P2O7 groups. The (P2O7)4– anion group shows bent eclipsed conformation. A comparative study among anhydrous (α-, β- and γ-Co2P2O7) and hydrated forms (Co2P2O7·2H2O) of dicobalt pyrophosphates known in literature is presented.
Crystal structures and Raman spectra of Cu(OH)F and Cu3(OH)2F4
Authors: Giester G. , Libowitzky E.
Published: December 2003

Crystals of Cu(OH)F and Cu3(OH)2F4have been synthesized at low-hydrothermal conditions in sizes up to 0.3 mm. The structures were solved from CCD X-ray single-crystal data and refined toR= 0.033 and 0.019, respectively.

Cu(OH)F: space groupP21/a,Z= 4,a= 5.301(1) Å,b= 6.376(1) Å,c= 5.074(1) Å,β= 112.90(1)°, andV= 157.98(5) Å3.

Cu3(OH)2F4: space groupP21/n,Z= 2,a= 5.501(1) Å,b= 4.766(1) Å,c= 8.462(1) Å,β= 92.28(1)°, andV= 221.68(7) Å3.

In both compounds the copper atoms are 4 + 2 coordinated to their ligands (Jahn-Tellerdistortion). Cu(OH)F is isotypic to Cu(OH)Cl, forming layers of edge-sharing Cu(OH)3F3polyhedra, which are interconnected by hydrogen bonds. The structure of Cu3(OH)2F4is characterized by chains of edge-sharing Cu(OH)2F4polyhedra running along [1 0 0], which are linked to each other via corners to form a framework. Hydrogen bonds of the type O—H···F occur with O···F distances of 2.619 and 2.697 Å in Cu(OH)Fand Cu3(OH)2F4, respectively. The observed O—H stretching frequencies of 3129 and 3306 cm–1, respectively, in Raman spectra are in excellent agreement with expected values from distance — frequency correlations. Moreover, the pleochroism of the bands corresponds in both compounds to the O—H orientation found in the structure determination.
Crystal chemistry of lead oxide phosphates: crystal structures of Pb4O(PO4)2, Pb8O5(PO4)2 and Pb10(PO4)6O
Authors: Krivovichev Sergey V. , Burns Peter C.
Published: December 2003

Crystals of three Pb oxide phosphates, Pb4O(PO4)2, Pb8O5(PO4)2 and Pb10(PO4)6O, were synthesized from mixtures of PbO and NH4H2PO4 heated to 950 °C. The crystal structure of Pb4O(PO4)2 (monoclinic, P21/c, a = 9.4894(8), b = 7.1402(6), c = 14.4077(13) Å, β = 104.549(2)°, V = 944.91(14) Å3) was solved by direct methods and refined to R1 = 0.044 (wR = 0.103). It contains isolated OPb4 tetrahedra that are linked through Pb—O bonds to O atoms of PO4 tetrahedra. The crystal structure of Pb8O5(PO4)2 (monoclinic, C2/m, a = 10.6427(4), b = 10.2078(4), c = 14.3530(6) Å, β = 98.325(1)°, V = 1542.86(11) Å3) was solved by direct methods and refined to R1 = 0.032 (wR = 0.068). It is based upon a complex sheet with composition [O5Pb8]. The basic element of the sheet is a cluster of composition [O5Pb10] that consists of four OPb4 tetrahedra that share edges. The adjacent [O5Pb10] clusters are linked by sharing Pb atoms, resulting in sheets that are parallel to (001). The PO4 tetrahedra are located in the interlayers between the sheets. The crystal structure of Pb10(PO4)6O (hexagonal, P63/m, a = 9.8650(3), c = 7.4306(3) Å, V = 626.25(4) Å3) has been solved by direct methods and refined to R1 = 0.040 (wR = 0.106). Pb10(PO4)6O crystallizes with an apatite-type structure. The structure contains a single O atom that is not part of a PO4 tetrahedron; it has a site occupancy factor of 0.25 and is located on the 63 axis.
Synthesis, structural and spectral studies of N-p-methylbenzyliden-N-phenyl-p,p′-dimethoxybenzoyl acetic acid hydrazide
Authors: Ülkü D. , Arıcı C. , Ercan F. , Saçmacı M. , Sarıpınar E. , Akçamur Y.
Published: December 2003

The structure of the organic derivative of N-p-methylbenzyliden-N-phenyl-p,p′-dimethoxybenzoyl acetic acid hydrazide, [C32H28N2O5], has been determined by X-ray diffraction. The structure derived from the NMR spectroscopy, the IR spectra and elemental analysis is consistent with that of the X-ray diffraction. The compound crystalizes in the monoclinic system with space group P21/c, a = 16.234(1), b = 9.399(2), c = 19.389(1), β = 110.924(3)°, V = 2763.3(5) Å3 and Z = 4. In the crystal, there is one weak C—H…O type intermolecular hydrogen bond interaction.
Crystal structure of an inclusion complex between chiral monoaza-15-crown-5 and S(–)-1-phenyl-ethyl ammonium percholorate
Authors: Özbey Süheyla , Kaynak F. B. , Toğrul M. , Demirel N. , Hoşgören H.
Published: December 2003

A new type of inclusion complex, S(–)-1 phenyl ethyl ammonium percholorate complex of R-(–)-2-ethyl - N - benzyl - 4, 7, 10, 13 - tetraoxa -1- azacyclopentadecane, has been prepared and studied by NMR, IR and single crystal X-ray diffraction techniques. The compound crystallizes in space group P21 with cell dimensions a = 10.0000(8), b = 12.281(2), c = 12.331(1)Å, β = 102.052(7), Z = 2 The host-guest complex is held together by a strong system of hydrogen bonds between the two protons of the ammonium ion as well as the nitrogen and four oxygen atoms of the crown ether The C—O and C—C distances of the 15-membered ring average 1.418 and 1.501 Å while the O—C—C and C—O—C angles average 110.2 and 113.3°. The average N—C distance is 1.476 Å.
Crystal structure of the K, Ti analogue of ilímaussite-(Ce), (Ba,K,Na,Ca)11–12(REE,Fe,Th)4(Ti,Nb)6(Si6O18)4(OH)12·4.5 H2O: revision of structure model and structural formula
Authors: Krivovichev Sergey V. , Yakovenchuk V. N. , Armbruster Th. , Pakhomovskiy Y. A. , Depmeier W.
Published: December 2003

The crystal structure of the K, Ti analogue of il¡maussite-(Ce), (Ba,K,Na,Ca)11–12(REE,Fe,Th)4(Ti,Nb)6(Si6O18)4(OH)12·4.5 H2O, from the Yukspor mountain, Khibiny massif, Kola peninsula, Russia, has been solved by direct methods and refined to R
1 = 0.077 on the basis of 1762 reflections with |F
o| ≥ 4σ
F. The mineral is rhombohedral, R32, a = 10.708(2), c = 60.073(11) Å, V = 5965.2(17) Å3. The structure is based upon a heteropolyhedral framework that consists of layers of corner-linked polyhedra. The SiO4 tetrahedra share corners to form 6-membered rings which are further interlinked via REEO6 trigonal prisms and Tiφ
6 octahedra (φ = O, OH). The obtained structure model is different from that recently reported by Rastsvetaeva et al. (2003) which is considered incorrect.
Analytic expressions for the vertex coordinates of quasiperiodic lattices
Authors: Naumis G. G. , Aragón J. L.
Published: December 2003

Using the generalized dual method, closed analytical expressions for the coordinates of quasiperiodic lattices, derived from periodic or quasiperiodic grids, are given. The obtained formulae constitute a useful and practical tool to generate and perform calculations in quasi periodic structures.
The hydrogen bond system of Mn-leonite: neutron diffraction results in comparison with IR spectroscopic data
Authors: Hertweck B. , Libowitzky E. , Schultz A. J.
Published: December 2003

Single-crystal Time-Of-Flight (TOF) neutron diffraction data of Mn-leonite, K2Mn(SO4)2·4 H2O, were obtained at 110, 185 and 295 K. Two reversible phase transitions at low temperatures have been previously confirmed by optical, calorimetric, and X-ray data. The cause for the phase transitions of Mn-leonite is a dynamic disorder of sulphate groups at room temperature (C2/m), that freeze to an ordered structure (I2/a) at 205(1) K. At 169(1) K the crystal structure switches to another ordered phase (P21/a).In general, the investigation by neutron diffraction confirms the structures of the three phases and, in addition, reveals the changes of the hydrogen bond configurations which influence the cooperative arrangement of the tetrahedra during the two successive phase transitions observed in Mn-leonite. IR spectroscopic measurements in the range of the O—H stretching frequencies yield a broad absorption band at ~3200 cm–1 that can only be resolved at low temperatures. A distance-frequency plot, calculated from the experimental data of low temperature neutron diffraction and IR spectroscopy is in agreement with correlation data from literature.
High pressure mixed alkali disilicates in the system Na2— xKxSi2O5: hydrothermal synthesis and crystal structures of NaKSi2O5-II and Na0.67K1.33Si2O5
Authors: Rakić S. , Kahlenberg V. , Schmidt B. C.
Published: December 2003

Single crystal growth experiments for NaKSi2O5 and Na0.67K1.33Si2O5 have been successfully performed by hydrothermal crystallization of two glasses at 500°C and 1 kbar during 24 hours. For a glass with a Na : K ratio of 1 : 1 a previously unknown NaKSi2O5 modification named phase II was obtained. The structure of NaKSi2O5-II has been solved from a single crystal diffraction data set and refined to a residual of R(|F|)= 0.032 for 1186 independent reflections. The compound is monoclinic with space group P21/c (a = 4.852(1) Å, b = 13.594(2) Å, c = 7.463(1) Å, β = 91.20(2)° V = 492.1(2) Å3, Mr
= 198.27 u, Z = 4, Dx
= 2.68 g/cm3, μ(MoKα
) = 1.58 mm–1) and belongs to the group of double chain silicates. Individual double chains can be described as being built by the condensation of zweier single chains of SiO4-tetrahedra running parallel to the a-axis. Each chain contains four-membered rings. Alkali-atoms are 6- and 8-fold coordinated by the oxygen ligands. NaKSi2O5-II is isotypic with the structure of NaRbSi2O5 which has been synthesized at room-pressure. Hydrothermal treatment of a second glass with composition Na0.5K1.5Si2O5 resulted in the formation of single-crystalline material of Na0.67K1.33Si2O5, slightly Na-richer than the starting composition. The platy crystals showed twinning by pseudo-merohedry, a feature we took account of by separating the reflections from the different twin individuals during the data collection. Structure solution has been accomplished by direct methods. The subsequent refinement converged to a residual of R(|F|) = 0.037 for 1543 independent reflections. The compound is mono clinic as well with space group I2/a (a = 12.731(2) Å, b = 7.321(1) Å, c = 17.827(3) Å, β = 100.85(2)° V = 1631.9(6) Å3, Mr
= 206.32 u, Z = 12, Dx
= 2.53 g/cm3, μ(MoKα
) = 1.78 mm–1) and belongs to the group of single layer silicates. A single layer consists of four-, six- and eight-membered rings, which are parallel to (100), and can be described as being built by the condensation of unbranched dreier single chains running along the b-axis. The stacking of the layers results in a three-dimensional structure in which the alkali cations reside between the layers for charge compensation. The distribution of the alkali atoms among the three crystallographically different positions M(1), M(2) and M(3) shows a definite preference of the larger potassium for the M(1) and M(2) site; the M(3) site is K-free. The alkali-atoms are 5- and 6- fold coordinated by the oxygen atoms. The geometrical and topological features of the single tetrahedral sheets in Na0.67K1.33Si2O5 are very similar to those observed in the phase I of NaKSi2O5. Differences can be attributed to different ways of stacking of adjacent sheets, and different sequences of up and down pointing tetrahedra within the rings.