Showing papers in "Zeitschrift Fur Kristallographie in 1990"

Geometrische Größen und einfache Modellrechnungen für BO4-Gruppen

Abstract: Most B04-groups deviate significantly from a regulär tetrahedron with symmetry 4 3 m T h e geometry of these deviations and the extent of the distortions are the main topics of this study. The shaf>es of 256 borate groups in 128 Compounds have been investigated. In BOs-groups with O • • • HO 3 distances shorter than 3 Ä the boron atom is displaced from the plane of the BOs-group towards the fourth oxygen atom. The displacement increases as the O • • • B distance decreases. Borate groups in orthorhombic and cubic boracites seem to represent the extreme distortions of OB'^ ''O3and Bt'^'04-groups, respectively. Mean B O distances of the 242 groups Vary from 1.444 to 1.534 Ä, individual B—O distances from 1.373 to 1.699 Ä [mean value = 1.476(35)Ä], individual O B 0 angles from 95.72 to 119.43° [mean value = 109.44(2.78)°]. Two simple models, e.g. a variant of a hybrid orbital model and a ligand repulsion model, have been used to calculate the shape of B04-groups with trigonal symmetry, which are in good agreement with those exjwrimentally determined.

The structure of quasicrystals

Abstract: The aim of the present article is to give a review of the state-ofthe-art on quasicrystal structure analysis. After a short discussion of the term \"crystal\" in chapter 1, the geometrical generation of quasilattices is touched in chapter 2. In the following the higher-dimensional description of Id, 2d and 3d quasi-crystals is demonstrated in detail as well as the derivation of structure factor equations and symmetry relationships in the higher-dimensional space. Chapter 4 shows the experimental techniques and structure determination methods for the study of quasicrystals. The experimental results of structural studies performed with different techniques are critically reviewed in chapter 5. Some of the results of the literature research are that five years after the detection of the first quasicrystal not a single quantitative (in terms of a regular structure determination) analysis of its structure has been carried out, and that the famous Mackay-icosahedra do not play the important role as the basic structural building elements as one supposed before. 1. What is a quasicrystal?

Structural hierarchy in M[6]T[4]ϕn minerals

Abstract: A large number of minerals have the general stoichiometry Αχ[ΜΎ*φΛ]γφζ, where A are large high-coordination number cations such as alkalis and alkaline earths, M are [6]-coordinate divalent to quadrivalent cations, T are [4]-coordinate trivalent to hexavalent cations, and φ are unspecified simple anions; the square brackets denote the more strongly bonded part of the structure, called the structural unit. This way of expressing a structural formula essentially gives a binary representation of the structure, whereby the structural unit can be considered as a very complex oxyanion that interacts with the A species that constitute the cationic part of the structure; the φ anions outside the square brackets are anions only very weakly held in the structure. There are two important features of expressing the formula in such a manner: (i) very complex interactions within the structure are reduced to a simple binary interaction that is susceptible to quantitative analysis using bond-valence theory; (ii) an hierarchical structural scheme may be set up by considering the graphical/ topological properties of the structural unit. Such a structure hierarchy is set up here for minerals with structural units of the general formula [MT<£„], based on the hypothesis that crystal structures may be ordered according to the polymerization of the coordination polyhedra of higher bond-valences. The structures are arranged into groups according to the dimension of polymerization of the structural unit, and are arranged within these groups in terms of increasing degree of polymerization. There is definitely a preferred sequence of polyhedral linkage with increasing degree of condensation: from a completely disconnected structural unit, there is linkage between octahedra and tetrahedra, followed by linkage between octahedra, followed by linkage between tetrahedra. Along with this is a systematic change in the stoichiometry of the structural unit; this suggests 2 Frank C. Hawthorne that in a chemical formula, there is much more structural information than we currently realize. The possible clusters of [M2T2„] stoichiometry are derived using graph theoretic and combinatorial techniques, subject to the boundary conditions that certain polyhedral linkages (e.g. face-sharing between tetrahedra) will not occur. There are 76 completely connected clusters of the form [M2T2<£„], but only 6 are found as fundamental building blocks in the structures of the 96 minerals considered here (in addition, there are a few minerals with structures based on fundamental building blocks larger than those considered here). The graphical characteristics of the clusters can be represented by the ordered integer string [abcdef], in which each integer represents the kind of linkage between different polyhedra. Defining 5 = (a + b + c + d + e + 0, S may take values in the range 3 — 8 for fully connected clusters subject to imposed stereochemical boundary conditions. Observed clusters fall in the range 3 — 6, the highly-connected clusters not being favoured. For S = 3, 4 and 5, there is one important cluster that is the basis of most structures for a given value of 5; for 5 = 6, there are two important clusters, one in which the tetrahedra share corners, and one in which the tetrahedra are not linked to each other. It seems that Nature selects only a few of the stereochemically possible clusters as fundamental building blocks, and produces structural diversity by polymerizing them in different ways. Introduction The \"rock-forming\" minerals are an extremely small subset of the mineral kingdom. Nevertheless, they have had the lion's share of scientific attention, particularly with regard to their role(s) in petrologic and geochemical processes. The structures of these minerals have one common characteristic: they are stable over a wide range of pressure, temperature and/or composition, one of the principal reasons why they are \"rock-forming\". The rest of the mineral kingdom is usually thought of as being composed of rare minerals that are not important in geological processes. Of course, this is not the case. Although they may be not as common as the rock-forming minerals, their very existence is a challenge to our understanding of geological processes. In addition, such minerals are important in many geological processes and environments. It is just that most of their occurrences are not fashionable to work on at the present time, as they tend to be resistant to conventional approaches based on equilibrium thermodynamics. In this class, we have such examples as highly fractionated pegmatites, the more chemically complex saline lakes, weathered zones over ore-bodies, soils, etc. Not only do such environments contain a large number of complicated minerals, but they often contain minerals of several different chemical types (e.g. silicates, phosphates, oxides, sulphates, sulphides and sulphosalts); such systems tend to resist the conventional approach to petrologic inΜ Ι61Τ141ψ„ minerals 3 terpretation. Moore (1973) and Hawthorne (1979) have suggested that the paragenetic sequences of minerals in such complex environments should be related to the crystal structures of the observed minerals. In this regard, it is useful to contrast the mineralogy of such environments with that observed in common rocks such as granites, granitoids, basalts, limestones, shales, etc. Whereas the latter consist of a small number of rock-forming minerals that adjust their chemistry (and structural state) in response to changing conditions, the former consist of large numbers of minerals that adjust their structure, i.e. break down to form new minerals (often of closely-related structure), in response to (even small) changes in ambient conditions. In common igneous and metamaorphic rocks, one normally follows the progressive evolution of the system via the changing chemistry (and structural state) of the consituent minerals. For those instances in which the structure rather than the chemistry changes with progressive evolution of the system, it makes sense to try and monitor such an evolving system through the progressive change in the crystal structures of the constituent phases. With this view in mind, hierarchical organization of mineral structures is necessary to interpret the crystallization processes that gave rise to the observed assemblages. Progress in the development of such a scheme for minerals has been intermittent over the past sixty years. Until recently, such schemes were forced to be rather specialized, as the structures of only a few common (normally rock-forming) minerals were known. The explosion in crystal structure work over the past twenty years has radically changed this situation. The structures of a considerable fraction of the accredited minerals have now been characterized, and this logistical barrier to a deeper understanding of mineral structures has been removed. Accordingly, there has been an increasing effort in this area over the past 10 years, particularly in the work of Liebau (1980, 1985), Lima-de-Faria (1983), Makovicky (1981, 1985), Moore (1982, 1984), Sabelli and Trosti-Ferroni (1985) and Hawthorne (1984 a, 1985,1986). All work has involved the character of the polymerization of structural units, but differs in detail, according to the general philosophy of the scheme or the exigencies of a particular structural group. Hawthorne (1983, 1985) has made the following proposals: (1) mineral structures may be ordered according to the polymerization of those cation polyhedra of higher bond-valence. (2) higher bond-valence polyhedra bond together to form homoor heteropolyhedral clusters that constitute the fundamental building block (FBB) of the structure. (3) the FBB is repeated (often polymerized) by translational symmetry operators to form the structural unit. For oxide and oxysalt structures, the structural unit constitutes a complex anionic polyhedral array (not necessarily connected) whose excess charge is balanced by the presence of (linking) large low-valence interstitial cations. 4 Frank C. Hawthorne General considerations Bond-valence theory (Brown, 1981) is a useful way of thinking about the structural chemistry of minerals, particularly when combined with the above three proposals. Of particular interest are the definitions of Lewis acid and base strengths, whereby the Lewis acid (base) strength of a cation (anion) is equal to the average bond-valence to that cation (anion), and the notion that base-strength can be defined for a complex anion. Also of interest is the bond-valence sum rule, whereby the sum of the bond-valences around an ion is approximately equal to the magnitude of the formal ion valence, and the valence-matching principle, which states that the most stable structures will form when the Lewis acid-strength of the cation(s) most closely matches the Lewis base-strength of the anions. From these definitions, one can than treat the structural unit as a complex anion, and calculate it's Lewis base strength; similarly one can calculate the Lewis acid strength of the interstitial cations. Doing this, one ends up with a binary representation of structure: a (usually) complex anion interacts (via the valence-matching principle) with the (often multiple) interstitial cations in the structure. I should emphasize that the structures are considered in this way not to convey the most complete picture of the bond-connectivity, but to express structure in a way such that one may apply bond-valence arguments to problems of structural chemistry. Thus one takes a complex structure and reduces it to a binary representation which may then be simply examined within the framework of bond-valence theory. Hawthorne (1985) has applied these proposals to set up a structural hierarchy for minerals based on tetrahedrally (T) and octahedrally (M) coordinated cations, and with the simplified formula MT20„, where φ = unspecific ligands. The present paper will co

The crystal structure of berlinite AIPO4 at high pressure

Abstract: La variete quartz du AlPO 4 cristallise dans P3 1 21 avec a=4,941 et c=10,940 A dans des conditions normales et a=4,605 et c=10,558 A a une pression de 8,51 GPa. L'augmentation de la presion entraine l'augmentation du rapport c/a et la diminution des angles (Al-O-P). Le changement du mode d'empilement de l'oxygene induit par l'augmentation de la pression est responsable du comportement a haute pression de AlPO 4 . L'influence des ions Al 3+ et P 5+ se manifeste en deformations locales dans le mode d'empilement

The crystal structures of CdAl2S4, HgAl2S4, and HgGa2S4

Abstract: CdAl 2 S 4 et HgGa 2 S 4 cristallisent dans I4. Les parametres de position du S sont x=0,2660, y=0,2770, Z=0,1352, affinement jusqu'a R=0,032 pour CdAl 2 S 4 et x=0,2718, y=0,2675, Z=0,1374, affinement jusqu'a R=0,042 pour HgGa 2 S 4 . HgAl 2 S 4 cristallise dans I42m. Hg est situe dans le site special (2a), 0,0,0 Al1 dans (2b) 0,0,1/2, tandis que Al 2 et la lacune sont distribues au hasard en (4d) 0,1/2, 1/4, affinement jusqu'a R=0,046. Les parametres de position pour S dans (8i) X, X, Z sont X=0,2272 et Z=0,3633

The solid phases of deuterium sulphide by powder neutron diffraction

Abstract: Powder neutron diffraction studies confirm that D2S has 3 solid-state phases at ambient pressure. Phases I and II are cubic and orientationally disordered with space groups Fm3m (a = 5.8486(8) angstrom at 160 K) and Pa3- (a = 5.7647(6) angstrom at 120 K), respectively. The deuterium scattering density arising from the disorder is modelled using symmetry-adapted spherical harmonic functions, which show a reduction from "twelve-fold" to "six-fold" disorder on cooling from phase I to phase II. For the fully ordered low-temperature phase III, a new structure has been determined which bears little resemblance to that reported in previous neutron diffraction study. The structure is orthorhombic, space group Pbcm, with a = 4.0760(1) angstrom, b = 13.3801(5) angstrom and c = 6.7215(3) angstrom at 1.5 K. The structure is essentially hexagonally close-packed, with distortions to accommodate the hydrogen atoms. The structure is antiferroelectric with the alignment of the molecular dipoles along the a direction.

Polarity determination in (001)-oriented AIII — BV compound semiconductors by the Kossel technique and chemical etching

Abstract: Analyse des profils de Kossel dans le but de determiner la polarite des composes semiconducteurs III-V orientees (001). Etant donne l'importance exceptionnelle de la differenciation entre les directions [110] et [110] sur la face (001) dans le cas des materiaux optoelectroniques, ces resultats ont ete compares aux resultats d'attaque chimique. Les axes longs des figures d'attaque sur la surface (001) s'alignent toujours parallelement a la direction [110]

Bestimmung der Kristallstruktur von T-Na3PO4 mit Röntgen- und Neutronenpulvertechniken

Abstract: Cristallisation dans P42 1 c avec a=1080,84, c=681,78 pm, (a T<601 K). Affinement jusqu'a R=0,041 (RX) et 0,080 (neutrons). Dans la phase a T<601 K les positions de Na et P ne changent pas par rapport a H-Na 3 PO 4 . Par contre, les groupes PO 4 sont completement ordonnes par rapport a leurs orientations

The crystal structure of δ-yttrium pyrosilicate, δ- Y2Si2O7

Abstract: The Single crystal structure of the high temperature phase, ^-YzSijOv, has been established by X-ray diffraction. Crystal data: YjSizOv, M = 346.0; orthorhombic, Pnam, a = 13.655(5), b = 5.016(3), c = 8.139(3) Ä; V = 557.5 Ä^ D, = 4.121 g c m ^ Z = 4. A(MoKa) = 0.71069 Ä, ß{yio-KoL) = 21.2 mm\" ^ /1[000) = 648 electrons, room temperature; Ä = 0.077 for 294 reflections. The structure proves to be similar to that proposed in the space group Pnal, for GdjSizOv by Smolin and Shepelev (Acta Crystallogr. 26B (1970) 484 492). The present work suggests that the space group Pnam provides an adequate representation of this structure type in the case of Y2Si207.

Crystal structure of mimetite, Pb5(AsO4)3Cl

Abstract: Mimetite Pb(AsO)Cl, M=1488.21 Daltons, space group P6/m, a=10.250(2), c=7. 454(1)A, U=678.214(2)A, Z=2, D=7.26 g cm, λ=1.237A, μ(neutron)=2.85 cm. The structure of the lead chloroarsenate mineral, mimetite, an isomorph of apatite, was refined using single crystal neutron diffractometry [R(189 hkl)=0. 057].

Crystal structures of rare earth elements rich apatite analogues

Abstract: The crystal structures have been determined for britholite-(Ce) and lessingite-(Ce) from the type localities and a third sample ('min X') showing chemical similarities to both britholite-(Ce) and lessingite-(Ce). This sample is from the Ilimaussaq intrusion in Greenland. They are rare earth elements (REE) rieh apatite analogues. Based on the X-ray diffraction results they were assigned to the hexagonal system with cell dimensions slightly larger than those of apatite. The three structures have been refined in the space group P63 to R values: 0.033 [britholite-(Ce)], 0.039 [lessingite(Ce)] and 0.036 ('min X'). The site occupancy factors for the REE atoms are in good qualitative agreement with results from electron-microprobe analysis. The lowering of the Space group symmetry relative to the apatite structure originates in differences in the oxygen positions. There is only analogy between one of the oxygen atoms of the SiOj\" and the oxygen atoms in apatite. The two REE sites found on threefold axis which correspond to Ca(l) in apatite are both nine-coordinated, but display significant variations in their REE — O distances. The REE found in a general position is seven-coordinated and similar to Ca(2) in apatite.

High-Resolution Transmission Electron Microscopy and Associated Techniques

Abstract: Many people are trying to be smarter every day. How's about you? There are many ways to evoke this case you can find knowledge and lesson everywhere you want. However, it will involve you to get what call as the preferred thing. When you need this kind of sources, the following book can be a great choice. high resolution transmission electron microscopy and associated techniques is the PDF of the book.

Neutron powder investigation of CuI

Abstract: Cul is known to undergo two phase transitions at T^ = 367° C and 7̂ 2 = 407° C. The structural changes involve a rearrangement of the anions and disordered distributions of the cations. The low temperature 7-phase has zincblende structure, space group F43m [a = 6.0337(3) A, Z = 4], The intermediate /S-phase belongs to the hexagonal system with a hcp anion lattice [a = 4.289(9) Ä), c = 7.189(5) Ä, Z = 2], space group P6m2 (coexisting with yor a-phase). The high temperature a-phase is cubic again, the anions form a fcc lattice and the c^ions are randomly distributed Over all tetrahedral sites, space group Frrßm [a = 6.148(1) Ä, Z = 4]. A modified powder profile refinement program, which includes anharmonic temperature factors, was used for the refinement of Cul at different temperatures and probability density functions were calculated to elucidate the diffusion paths of this high temperature superionic conductor. Different models were tried with anharmonic coefTicients upto the fourth order and split models with anisotropic temperature factors. With increasing temperature the density of Cu cations begins to spread from the center of the tetrahedra towards the vacant octahedral interstices. Aproaching the (x-ß transition from above the lobes near the tetrahedral faces become more pronounced indicating a transition from a diffusion to a more static (jump) behaviour near the phase transition. * This research werk was supported by funds of the BMFT (03SC1LMU). Permanent address: Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China. 8 0 Yu Yude. H. Boysen and H. Schulz

Single crystal structure refinement of MnCl2

Abstract: Confirmation de la cristallisation dans R3m, type structural C-19; avec a=3,711 et c=17,59 A, affinement jusqu'a R=0,105. Les octaedres MnCl 6 sont legerement aplatis suivant l'axe d'ordre trois

Elastic and thermoelastic properties of isotypic KClO4, RbClO4, CsClO4, TlClO4, NH4ClO4, TlBF4, NH4BF4 and BaSO4

Abstract: Elastic and thermoelastic constants of single crystals of KCIO4, RbC104, CsC104, T1C104, NH4C104, T1BF4, NH4BF4 and BaS04 have been determined from ultrasonic resonance frequencies. All members of this isotypic group exhibit similar elastic properties in respect to absolute magnitude, anisotropy and temperature dependence. Perchlorates possess slightly larger elastic constants compared to those of fluoroborates. The ammonium salts show a depression of the elastic stiffnesses due to a smaller exponent of the repulsive potential. Similar elastic properties are observed for BaS04. However, the mean elastic stiffness is much smaller than that estimated from a simple ionic model. Furthermore, the thermoelastic constants of BaS04 are also about a factor 1/3 smaller in absolute magnitude than those of the isotypic Perchlorates and fluoroborates.

The crystal structure of barite, β-BaS04, at high temperatures

Abstract: The crystal structure of barite: ^-BaS04 (orthorhombic, Pnma, Z = 4, = 4.48 g/cm^ at 25°C, /i = 120 cm\"' at 25°C, ß ->• a. transition temjjerature 1090°C) has been studied with Single crystal X-ray diffraction methods at temperatures up to 1035°C. The a-axis keeps expanding at elevated temperatures, while the expansion of the i-axis nearly ceases, and that of the c-axis ceases from 1010° C. The scatter of the interatomic Ba—O and Ba—S distances tends to decrease at temperatures above 900° C, while that of the S 0 distances increases. Inspection employing the O'KeeffeVoronoi polyhedron constructed around Ba reveals a change in coordination character above 900° C. The results suggest that a premonitory movement of the atoms begins at temperatures between 900° C and 1000°C and the final transition is triggered by excessively strained arrangements of the atoms within the structure.

A neutron powder diffraction study of the β to γ phase transformation in NaFeO2

Abstract: Etude de la transformation de phase β, (basse temperature, Pn2 1 a) en γ (haute temperature, PH 1 2 1 2) dans NaFeO 2 par analyse de Rietneld des donnees de diffraction de neutrons, dans le domaine de temperatures compris entre 298 et 1373 K. La transformation comporte des rotations cooperatives des tetraedres FeO 4 , des relocalisations des atomes d'oxygene autour des atomes de sodium, l'augmentation de l'angle Fe-O-Fe et des effets de memoire

Crystal growth and properties of rubidium titanium oxide phosphate, RbTiOPO4

Abstract: Les monocristaux de RbTiOPO 4 obtenus par la methode du fondant atteignent les dimensions 15×44×34 mm. Determination de differents parametres: cristallins, optiques, electrooptiques et electriques. Discussion sur la conductivite et le phenomene de courant spontane, ainsi que sur la transition ferroelectrique. La variation avec la temperature de la constante dielectrique indique une transition de phase du 2eme ordre a 829+1 o C

The crystal structure of lintisite, Na3LiTi2[Si2O6]2O2· 2H2O, a new titanosilicate from Lovozero (USSR)

Abstract: Na 3 LiTi 2 Si 4 O 14 2H 2 O cristallise dans C2/c avec a=28,583, b=8,600, c=5,219 A, β=91.03˚, affinement jusqu'a R=0,033. La structure consiste en chaines des tetraedres de [SiO 4 ], chaines des octaedres (a une arete commune) de [TiO 6 ] et [Na(O,H 2 O) 6 ], colonnes des tetraedres (a une arete commune) de [LiO 4 ] et cubes deformes de [NaO 8 ]

Crystal structure refinements of CoSO4 and NiSO4: very short interpolyhedral O — O contacts

Abstract: Nouvel affinement des structures orthorhombiques centrees de CoSO 1 et NiSO 4 jusqu'a R=0,0034 et 0,049. Ces composes cristallisent dans Cmcm avec a=5,192 et 5,166, b=7,856 et 7,846, c=6,530 et 6,362 A, C=4. Les octaedres metalliques MeO6 forment des chaines s'etendant le long de [001] et liees entre elles par des tetraedes SO 4 . L'octedre est plus deforme dans le compose du cobalt. La distance O-O enterpolyedre est particulierement courte dans ces composes: 2,687 A dans NiSO 4 , 2,722 A pour CoSO 4

Syntheses and crystal structures of α methyl alaninium dihydrogen monophosphate and Lβ methyl alaninium dihydrogen monophosphate. An approach for the design and preparation of polar organic-inorganic materials

Abstract: [(CH 3 ) 2 C(NH 3 )COOH] + •H 2 PO 4 − (α MADP) cristallise dans P1 avec a=10,060, b=7,634, c=5,852 A, α=97,32, β=107,5, γ=81,16 o , Z=2, affinement jusqu'a R=0,026; [CH 3 CH 2 CH(NH 3 ) COOH) + •H 2 PO 4 − (LβMADP) cristallise dans P2, avec a=7,164, b=6,533, c=9,458 A, β=105,48 o ; Z=2, affinement jusqu'a R=0,033. La structure en couches de αMADP et la structure en chaines de LβMADP mettent en evidence l'importance de l'ion polymere H 2 PO 4 − et son utilisation possible dans le dessin de la structure des materiaux inorganique polaires

The crystal structure of Ca0.8Mg1.22Si2O6clinopyroxene (Di80En20) atT= -130°, 25°, 400° and 700°C

Abstract: Le clinopyroxene synthetique du titre cristallise dans C 2 /c, l'affinement varie entre 2,9 et 4,9% (a des temperatures comprises entre −130 et 700 o C). On observe la deformation du polyedre M2, avec l'augmentation de la temperature entrainant la diminution de 8 a 6 de la coordination du Ca. La deformation du polyedre M2 et le deplacement de la chaine tetraedrique permettent la maintenance des longueurs raisonnables des liaisons par la liberation de deux des quatre O3

Crystal growth and structure determination of potassium zirconium phosphate K2Zr(PO4)2

Abstract: Les cristaux obtenus en solutions fondues sont macles par merohedrie. K 2 Zr(PO 4 ) 2 cristallise dans P3 avec a=5,176, c=9,011 A, Z=1, affinement jusqu'a R=0,029. La structure consiste en couches de ZrO 6 compactes et perpendiculaires a l'axe c. Les tetraedres PO 4 sont legerement deformes

Crystal structure of 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTDA)

Abstract: C 14 H 4 O 6 cristallise dans P2 1 /c avec a=7,867, b=5,305, c=12,574 A, β=72,73 o , Z=2, affinement jusqu'a R=0,042. La molecule presente un centre d'inversion. Il y a un bon accord entre les longueurs des liaisons equivalentes chimiquement, confirmant la distance carbonyle courte (1,185 A). Le cristal est constitue d'empilements suivant b des molecules NTDA qui se recouvrent seulement d'une facon partielle

Die Kristallstruktur von Ag6[B12O18(OH)6] ⋅ 3 H2O, einem neuen Dodekaborat

Abstract: Cristallisation dans P2 1 /c avec a=1178,4, b=1065,4, c=1011,6 μm, β=112,10 o , Z=2, affinement jusqu'a R=4,7%. La structure contient l'ion [B 12 O 18 (OH) 6 ] 6− . Deux ions Ag + occupent statistiquement leurs positions avec une molecule H 2 O par maille unitaire

Verfeinerung der Kristallstruktur von p-PtP2

Abstract: Affinement de la structure cristalline du PtP 2 de type pyrite par diffraction Rx sur monocristal. L'amelioration des parametres structuraux donne un affinement de R=1,7%. Les parametres 4 sont respectivement 0,38956 et 0,3896 (a=569,68 pm, 295 K)