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The work function for emission of alkali ions M+ (M = Li, Na, K, Rb, Cs) from two different types of alkali aluminosilicates, MAlSi2O6 and MAlSiO4, has been investigated by means of thermionic emission. The work functions w fall in a range between 1.0 and 2.5 eV. The work function decreases in the order w(Li+) > w(Na+) > w(K+) > w(Rb+) > w(Cs+). This decrease is correlated with a concomitant increase in the ionic radius of the alkali ion. The work function also increases with increasing ionization energy of the neutral alkali atom.

Partial vapour pressure of oxygen in contact with materials is considered as a key parameter which influences the oxidation processes stimulating the formation of variety of oxidation products. In this work manganese oxide nanorods; Mn 5 O 8 and β-MnO 2 have been prepared by isothermal decomposition of manganite (28 nm) precursor in air. Calcination temperature and amount of oxygen accessible to the precursor are crucial parameters that affect the decomposition pathway. X-ray single phase Mn 5 O 8 is obtained by calcination of manganite at 350 °C in small size glass tube for 1 h; the case in which slight amount of oxygen is in close contact with the surface of the precursor. Using large size tube β-MnO 2 is produced. Morphological investigations showed that the precursor has rod like morphology and the transformations to the corresponding oxide are isomorphous approaches. The studies of the magnetic properties of Mn 5 O 8 showed the existence of tiny amount of impurities related to the presence of the spinel Mn 3 O 4 (0.4%) into the sample. Presence of these impurities is explained on the base of accumulation of some unreacted Mn(OAc) 2 over the surface of manganite precursor which is evidenced by IR analysis. By annealing of manganite at higher temperatures, Mn(OAc) 2 decomposes leading to formation of the spinel.

In this study, three distinct preparative routes to nanocrystalline (nc) CoOOH yielding compositionally and structurally specifiable materials, which are all closely related to clean CoOOH are presented. Simple precipitation–oxidation and oxidation–precipitation routes using atmospheric oxygen or Br2 dissolved in an aqueous solution of NaOH as an oxidising agent lead to the various products. The purified solids were characterised by means of X-ray powder diffraction (XRPD), chemical, thermal and thermogravimetric analyses, magnetic measurements, and, based on synchrotron data, by means of pair distribution function (PDF) analyses. The chosen routes led to nanocrystalline materials differing in the mean size of the coherently scattering domains (7 nm and 24 nm), in the lattice parameter c, in the relative amount of released mass in the course of conversion into cobalt oxide spinel and the residual relative amount of non-oxidised Co(II). The incomplete oxidation of Co(II) is associated with a molar ratio nH/nO > 0.5 that is found to be the origin of stacking fault disorder in the materials. Possible models of disorder were derived from structural considerations and tested by DIFFaX simulations. A recursive routing for refining the microstructure by global and local optimisation of the measured powder patterns was applied to each sample. Crystal intergrowth of the (AcB)(BaC)(CbA) stacking pattern of clean CoOOH and that of (AcB)(AcB) brucite type Co(OH)2 was identified as a main feature of the microstructures of the three diverse CoOOH-type samples. PDF analyses corroborate the derived microstructural models.

Transition metal dichalcogenides (TMDC) are important representatives in the emerging field of two-dimensional materials. At present their combination with molecular films is discussed as it enables the realization of van der Waals bound organic/inorganic hybrids which are of interest in future device architectures. Here, we discuss the potential use of molybdenum disulfide (MoS2) as supporting substrate for the growth of well-defined, crystalline organic adlayers. By this means, hybrid systems between the TMDC surface and organic compounds can be prepared, allowing for the profound investigation of mutual optical and electronic coupling mechanisms. As model system, we choose pentacene and perfluoropentacene as prototypical organic semiconductors and analyze their film formation on MoS2(001) surfaces. In both cases, we observe smooth, crystalline film growth in lying molecular configuration, hence enabling the preparation of well-defined hybrid systems. By contrast, on defective MoS2 surfaces both materials adopt an upright molecular orientation and exhibit distinctly different film morphologies. This emphasizes the importance of highly ordered TMDC surfaces with low defect density for the fabrication of well-defined hybrid systems.

Nanocrystalline cobalt hydroxide oxide (nc-CoOOH) particles were synthesized via a precipitation-oxidation mechanism with different oxidation agents. Since the choice of the oxidative compound is of great practical importance, we compared the properties of the nc-CoOOH particles obtained from the oxidation with O2 and Br2. The particles from both synthesis routes were fully characterized with X-ray powder diffraction (XRPD), infrared spectroscopy (IR), superconducting quantum interface device (SQUID) measurements, X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) measurements. It was found that the choice of the oxidation agent greatly affects the properties of the resulting nanoparticles; the most significant differences concern particle size and magnetic moment, due to residual Co2+. Although both, Br2 and O2, lead to the formation of nc-CoOOH, particles obtained from the synthesis involving O2 show a three times larger particle size than their counterparts obtained from the synthesis using Br2 (24 nm vs. 8 nm). Furthermore, using Br2 during the synthesis leads to an 8-fold increase of the amount of residual Co2+ impurities, which, in fact, induce a magnetic moment. A possible enrichment of those Co2+ impurities on the surface of the nanoparticles is discussed based on XPS and NEXAFS data.

We investigated the compound 1T-Cu

In this report, fructose-derived carbonaceous spheres were utilized as sacrificial templates for the fabrication of metal oxide hollow spheres (MOHSs) by a facile hydrothermal approach. Hollow spheres of a series of crystalline metal oxides (α-Fe2O3, Cr2O3, Co3O4, NiO, and ZnO) have been fabricated, utilizing the metal chloride as the oxide precursors. Heating of an aqueous solution of the metal chloride and fructose to moderate temperature in an autoclave affords a spherical composite consisting of a metal precursor shell sheathing a carbonaceous core. Subsequent removal of the interior carbonaceous cores by thermal treatment through oxidation in air produces free-standing crystalline oxides hollow spheres. The MOHSs were characterized by means of SEM, TEM, XRD, IR spectroscopy, energy dispersive X-ray (EDX) and sorption measurements. The results show convincingly that using fructose as a sacrificial template after application of a hydrothermal synthesis route could be a favourable sacrificial template for the fabrication of various MOHSs.

We investigated the synthesis of carbonaceous spheres(CSs) via hydrothermal hydrolysis of aqueous solution of monosaccharides (glucose and fructose) in closed system. Different synthesis parameters such as temperature, reaction time, and sugar concentration are important for tuning the diameter of the CSs. In addition, control over the size of the CSs can be achieved using acetic acid as a size-determining agent. The results show that important differences have been observed between both glucose and fructose derived CSs. For the production of well defined CSs the hydrothermal hydrolysis of fructose show lower reaction temperature and shorter reaction time if compared with hydrothermal hydrolysis of glucose. The particle sizes, however, are smaller when glucose is utilized as source of the CSs.

A simple series of test-tube experiments is all it takes to quantify a largely neglected nano-effect responsible for a dramatic increase-by orders of magnitude-in the surface-area-normalized rate of dissolution of nanocrystals. Though the observed variation in this specific rate as a function of size is unprecedented, the effect may be rationalized in terms of the classic atomistic theory of crystal growth and dissolution.

While HRTEM is the well-established method to characterize the structure of dodecagonal tantalum (vanadium) telluride quasicrystals and their periodic approximants, phase-contrast imaging performed on an aberration-corrected scanning transmission electron microscope (STEM) represents a favorable alternative. The (Ta,V)151Te74 clusters, the basic structural unit in all these phases, can be visualized with high resolution. A dependence of the image contrast on defocus and specimen thickness has been observed. In thin areas, the projected crystal potential is basically imaged with either dark or bright contrast at two defocus values close to Scherzer defocus as confirmed by image simulations utilizing the principle of reciprocity. Models for square–triangle tilings describing the arrangement of the basic clusters can be derived from such images.

The eightfold 2a0×2b0×2c0 superstructures of 6R-CuxTa1+yS2 are reported for crystal A with x = 0.237 and y = 0, and crystal B with x = 0.23 and y = 0.06. Compelling evidence is presented for the self-intercalation of tantalum onto octahedral sites, based on the diffraction data and crystal chemical arguments. The eightfold superstructure is formed by partial vacancy ordering within planes of intercalated atoms, while the stacking of TaS2 layers remains that of the 6R polytype. Temperature-dependent X-ray diffraction experiments show that the superstructure exists between T = 14 K and at least 370 K. Intercalated atoms enter the compound at octahedral and tetrahedral sites in alternating Van der Waals gaps. Intercalation is inhomogeneous, with average occupancies varying between 0.11 for octahedral sites within one Van der Waals gap and 0.23 for the tetrahedral sites within another Van der Waals gap. It is proposed that partial vacancy ordering is governed by the principle of maximum separation between intercalated atoms.

It is pointed out that the most important open question posed by the anomalous uncompensated magnetic moment of nanosized antiferromagnets is largely overlooked today, 54 years after Richardson’s discovery of the phenomenon and 49 years after Néel’s explanation of it.

A hydrothermal route to synthesize tantalum pentoxide (Ta 2 O 5 ) hollow spheres (TPHSs) using tantalum pentaethoxide (Ta(OET) 5 ) as the oxide precursor and glucose-derived carbonaceous spheres (CSs) as the sacrificial templates have been described. The carbonaceous spheres (CSs) were first prepared by hydrothermal carbonization of glucose, then a controlled coating of the template surface by Ta 2 O 5 nanoparticles via the hydrolyzing of tantalum pentaethoxide at ambient temperature was implemented. Subsequent removal of the interior carbonaceous cores by pyrolytic treatment through oxidation in air produces freestanding TPHSs. The obtained TPHSs were characterized by means of SEM, TEM, XRD, and IR spectroscopy.

We investigated the compound 1T-Cu x Ta1-x S2 with respect to its synthesis, homogeneity range, structure and electronic properties. The average structure of 1T-Cu x Ta1-x S2 resembles that of the high-temperature phase of the layered transition metal dichalcogenide 1T-TaS2 in which tantalum is partially substituted by copper. 1T-Cu x Ta1-x S2 readily decomposes at elevated temperatures and can only be prepared and stabilized by a sufficiently high amount of sulfur excess. XPS and NEXAFS measurements reveal that copper has the oxidation state +I in 1T-Cu x Ta1-x S2, which is supported by quantum chemical calculations. The disorder introduced by copper doping causes an Anderson-type localization of the conduction electrons as manifested by a strong increase of the electrical resistivity and a Curie-type paramagnetism at low temperatures as in other doped systems 1T-M x Ta1-x S2 with higher valent metals. Quantum chemical calculations support this interpretation.

An analysis of certain types of multiplicative congruential generators--otherwise known for their application to the sequential generation of pseudo-random numbers--reveals their relation to the coordinate description of lattice points in two-dimensional primitive sublattices. Taking the index of the lattice-sublattice transformation as the modulus of the multiplicative congruential generator, there are special choices for its multiplier which induce a symmetry-preserving permutation of lattice-point coordinates. From an analysis of similar sublattices with hexagonal and square symmetry it is conjectured that the cycle structure of the permutation has its crystallographic counterpart in the description of crystallographic orbits. Some applications of multiplicative congruential generators in structural chemistry and biology are discussed.

The monoclinic phase in the Al–Ta system has been identified by means of X-ray single-crystal structure analysis as Al19+ x Ta24− x (x = 1.6), Pearson symbol mP86. Al20.58Ta22.42 crystallizes in the space group P21/n, with a = 987.86 pm, b = 990.12 pm, c = 1489.45 pm and β = 99.958°. Twinned crystals of the title compound can be obtained by iodine-promoted reactions of the elements. In the experiments described here, the reactions took place in sealed tantalum ampoules at 1400°C. Single-phase samples were obtained by a metallurgical powder method, which minimizes aluminium loss by incongruent vapourization. The composition was found to span the range 0.51 ≤ x Ta ≤ 0.53. Al19+ x Ta24− x decomposes in the solid state at 1450°C into Al69Ta39 and σ-AlTa2. The crystal structure is analyzed in relation to tetrahedral close-packed structures. The kinship with Cr3Si-type and H-type structures is accentuated.

The boundary conditions and scope of catalytically stimulated synthesis of ordered intermetallics from solid metals are elucidated. The method is applied to the preparation of AlPd5. Its crystal structure has been determined by means of x-ray powder diffractometry. AlPd5 forms a structurally unmatched ordered variant of the cubic close-packing of spheres. Above 900 K AlPd5 is merged in the fcc boundary solid solution AlxPd1−x by a first order phase transition. The particular arrangement of the minority component Al and the associated structural distortions are analysed with regard to chemical bonding against the background of the enthalpy-driven disorder-order transition.

We present single-crystal studies of Pd(0.213)Cd(0.787) and Pd(0.235)Cd(0.765), synchrotron powder studies of Pd(1-x)Cd(x), 0.755or =xor =0.800, and LDA-DFT and extended Hückel (eH) calculations on these or related phases. The two single-crystal structures have a, b, and c axis lengths of 9.9013(7), 14.0033(10), 37.063(24) and 9.9251(3), 14.0212(7), 60.181(3) A, respectively and they crystallize in the space groups Ccme and F2mm, respectively (solved as (3+1)-dimensional crystals their most convenient superspace group is Xmmm(00gamma)s00). The structures have two different structural components each with their own separate axis parameters. Powder data shows that the ratio of these separate axes (S/L) varies from 1.615 to 1.64, values near the golden mean (1.618). For Pd(0.213)Cd(0.787), different Pd and Cd site occupancies lead to variation in the R factor from 2.6-3.6 %. The site occupancy pattern with the lowest R factor (among the 26 820 variants studied) is the exact site occupancy pattern predicted by LDA-DFT parameterized eH Mulliken charge populations. The phases can be understood through a chemical twinning principle found in gamma-brass, the parent structure for the above phases (a relation with the MgCu(2) Laves phase is also noted). This twinning principle can be used to account for Cd and Pd site preferences. At the same time there is a clean separation among the Cd and Pd atoms for the two separate chain types at height b=0 and 1/2. These results indicate that Cd:Pd stoichiometry plays a role in phase stability.

A series of metal oxides hollow spheres (Cr2 O3 , α-Fe2 O3 , Co3 O4 , NiO and ZnO) have been fabricated using the glucose derived-carbonaceous spheres as sacrificial templates and the metal chlorides as precursors for the metal oxides in a sacrificial templating process. Heating of an aqueous solution of the metal chloride and glucose in an autoclave at 180 oC affords - as indicated by transmission electron microscopy (TEM) - a nanospherical composite consisting of a metal precursor shell sheathing a carbonaceous core. Consequently, hollow crystalline oxides spheres are obtained by removal of the carbonaceous cores through calcination in air. Correlations between the particle size and the various synthesis conditions such as glucose concentration, the molar concentration ratio between glucose and metal chloride, temperature, reaction time and the addition of acetic acid as a catalyst are uncovered. The obtained metal oxides hollow spheres were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray powder diffraction (XRD), infrared spectroscopy (IR), and nitrogen adsorption/desorption isotherms (BET).

The crystal structure of the title compound has been determined by X-ray diffraction means. Pt 29 Zn 49 forms a complex superstructure of a defective AlB 2 -type derivative of the order 58: a = 279.0(1) pm, b = 11895.2(4) pm, c = 698.0(1) pm, space group Amm2 , Z = 2. Ordering of vacancies is accompanied by a particular distortion of defective graphite-like 6 3 nets consisting exclusively of Zn atoms. The ordering induces a modulation of the structure along a h of an AlB 2 -type structure with a periodicity of nearly 12 nm. A mechanistic model is proposed elucidating how Pt 29 Zn 49 evolves from the eutectoid decomposition of the inter-mediate high temperature precursor Pt 7 Zn 12 .

The synthesis, phase relations, and crystal structures of two truly ternary, partially ordered Laves phases occurring in the V—Co—Si system are reported. The phases termed L1 V(Co1–xSix)2 are found in two distinct phase fields next to TiMnSi-type VCoSi. This so-called E-phase emerges in the centre of the miscibility gap which separates the Co- and Si-rich Laves phase fields. Both fields accommodate several structurally distinct L-phases. The L1-phases V(Co1–xSix)2 (x = 0.43 and 0.56) crystallise in √3a × √3a superstructures of the hexagonal MgZn2 structure type. A rigorous symmetry-based analysis reveals that, at the given compositions, this type of superstructure affords sufficient structural degrees of freedom for ordering of Co and Si atoms on 4 different sites in a manner that enables tuning of hetero-atomic Co—Si interactions to an optimum.

The hydrogenation behavior of MgPd3 has been studied by in situ X-ray powder diffraction and by neutron powder diffraction. At room temperature and p ≈500 kPa hydrogen pressure its structure is capable of incorporating up to one hydrogen atom per formula unit (α-MgPd3H≈1), thereby retaining a tetragonal ZrAl3-type metal atom arrangement. Upon heating to 750 K in a hydrogen atmosphere of 610 kPa it transforms into a cubic modification with AuCu3-type metal atom arrangement ( β -MgPd3H≈0.7). Neutron diffraction on the deuteride reveals an anion deficient anti-perovskite-type structure ( β -MgPd3D0.67, a = 398.200 ( 7 ) pm) in which octahedral sites surrounded exclusively by palladium atoms are occupied by deuterium. Complete removal of hydrogen (480 K, 1 Pa) stabilizes a new binary modification ( β -MgPd3, a = 391.78 ( 2 ) pm) crystallizing with a primitive cubic AuCu3-type structure. Mechanical treatment (grinding) transforms both α and β modifications of MgPd3 into a cubic face-centered solid solution Mg0.25Pd0.75 showing a random distribution of magnesium and palladium atoms.

The crystal structure, its variation within the homogeneity range and some physical properties of the new zinc-rich, partly disordered phase Ir 7 + 7 δ Zn 9 7 - 1 1 δ (0.31≤δ≤0.58) are reported. The structures of three phases with distinct composition were determined by means of single crystal X-ray diffraction. Ir 7 + 7 δ Zn 9 7 - 1 1 δ exhibits a significant homogeneity range, adopts a complex γ-brass related cubic structure (cF403-406), is stable up to 1201(2) K, and transforms sluggishly below 1048(4) K into a phase with 394 atoms in the monoclinic primitive unit cell. It is a diamagnetic, moderate metallic conductor. Six distinguishable clusters consisting of 22-29 atoms comprise the structure. The clusters are situated about the 16 high symmetry points of the cubic F lattice. The structure can be subdivided into two partial structures, one with constant composition IrZn 5 and 192 atoms per unit cell and a second being significantly richer in zinc with variable composition and 211-214 atoms per unit cell. The meandering triply periodic minimal surface of two interpenetrating diamond-like nets separates the compositionally variable from its complementary invariant part. The phase width is coupled with substitutional and positional disorder. A comprehensive analysis of composition-dependent site occupancy factors reveals a linear correlation between the various types of disorder which can be conclusively interpreted in terms of an incoherent intergrowth of distinctive partial structures in variable proportions on a length scale comparable to the size of the approximately 2 nm large unit cell. On the basis of the structural findings we derive the structure chemically meaningful formula Ir 7 + 7 δ Zn 9 7 - 1 1 δ which quantitatively accounts for the interrelation between substitutional and positional disorder and provides a measure for the homogeneity range in structural terms.

The mixed-valent oxotantalate Eu1.83Ta15O32 was prepared from a compressed mixture of Ta2O5 and the metals in a sealed Ta ampoule at 1400 °C. The crystal structure was determined by means of single crystal X-ray diffraction: space group R3¯, a = 777.2(6) pm and c = 3523.5(3) pm, Z = 3, 984 symmetrically independent reflections, 83 variables, RF = 0.027 for I > 2σ (I). The structure is isotypic to Ba2Nb15O32. The salient feature is a [Ta(+8/3)6O12iO6a] cluster consisting of an octahedral Ta6 core bonded to 12 edge-bridging inner and six outer oxygen atoms. The clusters are arranged to slabs which are sandwiched by layers of [Ta(+5)3O13] triple octahedra. Additional Ta(+5) and Eu(+2) atoms provide the cohesion of these structural units. Twelve-fold coordinated Eu(+2) atoms are situated on a triply degenerate position 33 pm displaced from the threefold axis of symmetry. A depletion of the Eu(+2) site from 6 to 5.5 atoms per unit cell reduces the number of electrons available for Ta-Ta bonding from 15 to 14.67 electrons per cluster. Between 125 and 320 K Eu1.83Ta15O32 is semi-conducting with a band gap of 0.23 eV. The course of the magnetization is consistently described with the Brillouin function in terms of a Mmol/(NAμB) versus B/T plot in the temperature range 5 K — 320 K and at magnetic flux densities 0.1 T — 5 T. At moderate flux densities (< 1 T) the magnetic moment agrees fairly well with the expected value of 7.94 μB for free Eu (2+) ions with 4f7 configuration in 8S7/2 ground state. Below 5 K, anisotropic magnetization measurements at flux densities B < 1 T point to an onset of an antiferromagnetic ordering of Eu spins within the layers and an incipient ferromagnetic ordering perpendicular to the layers. Tantalcluster in oxidischer Matrix — Synthese, Kristallstruktur and magnetische Eigenschaften von Eu1.83Ta15O32 Das gemischt-valente Oxotantalat Eu1.83Ta15O32 wurde aus einer gepressten Mischung von Ta2O5 und den Metallen in einer geschlossenen Tantalampulle bei 1400 °C hergestellt. Die Atomanordnung wurde uber Einkristall-Rontgenstrukturanalyse bestimmt: a = 777.2(6) pm and c = 3523.5(3) pm, Raumgruppe R3¯, Z = 3, 984 symmetrisch unabhangige Reflexe, 83 Variablen, RF = 0.027 mit I > 2σ (I). Die Struktur ist isotyp zu Ba2Nb15O32. Die charakteristische Baugruppe der Struktur ist ein [Ta(+8/3)6O12iO6a]-Cluster bestehend aus einem oktaedrischen Ta6-Kern, an den 12 Oi-Atome μ2-verbruckend und 6 weitere Oa-Atome terminal gebunden sind. Die zu Schichten angeordneten Cluster sind von Schichten aus [Ta(+5)3O13]-Oktaedertripel sandwichartig umgeben. Zusatzliche Ta(+5)- und die Eu(+2)-Atome besorgen den Zusammenhalt dieser Struktureinheiten. Die zwolffach koordinierten Eu-Atome sind fehlgeordnet auf einer 18-zahligen Lage 33 pm entfernt von der dreizahligen Symmetrieachse. Eine Unterbesetzung von 5, 5 anstatt 6 Eu-Atomen pro Elementarzelle vermindert die fur Ta-Ta-Bindungen verfugbare Valenzelektronenzahl von 15 auf 14.67 e pro Cluster. Im Temperaturbereich 125 — 320 K ist Eu1.83Ta15O32 halbleitend mit einer Bandlucke von 0.23 eV. Der Verlauf der Magnetisierung lasst sich im Temperaturbereich 5 K — 320 K und bei magnetischen Flussdichten von 0.1 T — 5 T mit der Brillouin-Funktion als Auftragung von Mmol/(NAμB) gegen B/T quantitativ erfassen. Bei moderaten magnetischen Flussdichten stimmt das magnetische Moment oberhalb 5 K nahezu mit dem Erwartungswert von 7.94 μB fur freie Eu(+2)-Ionen mit 4f7-Konfiguration im 8S7/2-Grundzustand uberein. Richtungsabhangige Magnetisierungsmessungen bei Flussdichten B < 1 Tesla weisen unterhalb 5 K auf eine einsetzende antiferromagnetische Spinordnung in den Schichten dicht gepackter Atome und senkrecht dazu auf ferromagnetische Kopplungen hin.

The crystal structure of the ζ 1 -phase Al 3 Cu 4 was determined by means of X-ray powder diffraction: a = 812.67(3) pm, b = 1419.85(5) pm, c = 999.28(3) pm, space group Fmm2, Pearson symbol oF88-4.7, R I = 0.0633. The structure represents a distinctive 2a x 23a x 2c superstructure of a metal-deficient Ni 2 In-related structure. The ordering of the minor component and the vacancies in the atomic layers of hexagonal topology fulfill the principle of maximal self-avoidance.

The crystal structure of the ζ2-phase Al3Cu4-δ was determined by means of X-ray powder diffraction: a = 409.72(1) pm, b = 703.13(2) pm, c = 997.93(3) pm, space group Imm2, Pearson symbol oI24-3.5, RI = 0.0696. ζ2-Al3Cu4-δ forms a distinctive a × √3a × 2c superstructure of a metal deficient Ni2In-type-related structure. The phase is meta-stable at ambient temperature. Between 400 °C and 450 °C it decomposes into ζ1-Al3Cu4 and η2-AlCu. Entropic contributions to the stability of ζ2-Al3Cu4-δ are reflected in three statistically or partially occupied sites. Die Kristallstruktur von ζ2-Al3Cu4-δ Die Kristallstruktur von ζ2-Al3Cu4-δ wurde aus der Profilanpassung eines Pulver-Rontgendiffraktogramms bestimmt: a = 409.72(1) pm, b = 703.13(2) pm, c = 997.93(3) pm, Raumgruppe Imm2, Pearson Symbol oI24-3.5, RI = 0.0696. ζ2-Al3Cu4-δ bildet eine a × √3a × 2c Uberstruktur einer teilweise fehlgeordneten Ni2In-Typ-verwandten Struktur. Die bei Raumtemperatur metastabile Phase zerfallt zwischen 400 °C und 450 °C in ζ1-Al3Cu4 and η2-AlCu. Entropiebeitrage zur Stabilitat machen sich in einer Unter- beziehungsweise Gemischtbesetzung von drei Atom-Lagen bemerkbar.

The γ-brass type phase Pt2Zn11—δ (0.2 2σ (Io) for 293 symmetrically independent intensi ties and 19 variables. The structure consists of a 26 atom cluster which is comprised of four crystallographically distinct atoms. The atoms Zn(1), Pt(1), Zn(2) and Zn(3) form an inner tetrahedron IT, an outer tetrahedron OT, an octahedron OH, and a distorted cuboctahedron CO respectively. About 14 % of the Zn(1) sites are unoccupied. Pt2Zn10.73 melts at 1136(2) K. It is a moderate metallic conductor (ρ298 = 0.2—0.9 mΩ cm) whose magnetic properties (χmol = —4.6 10—10 to —5.4 10—10 m3 mol—1) are dominated by the core diamagnetism of its components. Struktur und Eigenschaften von Pt2Zn11—δ (0.2 < δ < 0.3) vom γ-Messing-Typ Die Phase Pt2Zn11-δ (0.2 2σ (Io), 293 symmetrisch unabhangigen Reflexen und 19 Variablen. Charakteristische Baugruppe der Struktur ist ein 26-Atom-Cluster, der aus vier kristallographisch unterschiedlichen Atomen aufgebaut ist. Die Atome Zn(1), Pt(1), Zn(2) und Zn(3) bilden ein inneres Tetraeder IT, ein auseres Tetraeder OT, ein Oktaeder OH beziehungsweise ein verzerrtes Kuboktaeder CO. Die Zn(1)-Lage ist zu etwa 14 % unterbesetzt. Pt2Zn10.73 schmilzt bei 1136(2) K. Die Verbindung ist ein masiger metallischer Leiter (ρ298 = 0.2—0.9 mΩ cm), dessen magnetische Eigenschaften (χmol = —4.6 10—10 to —5.4 10—10 m3 mol—1) vom Diamagnetismus der Atomrumpfe der Komponenten bestimmt werden.

Three new binary intermetallics in the palladium-rich part of the magnesium–palladium system have been identified and characterized by combining preparative methodologies with powder X-ray diffraction techniques and thermochemical analyses. MgPd2 decomposing in the solid state at 628(2)°C adopts a Co2Si-type structure: space group Pnma, a=5.4421(2), b=4.1673(2), c=8.0129(3) A. MgPd3 crystallizes in a Al3Zr-type structure: space group I4/mmm, a=3.92263(7), c=15.6527(4) A. It decomposes in a peritectoid reaction at 704(2)°C. The kinetics of the iodine-catalyzed synthesis of MgPd2 have been studied. The reactions seem to follow Ostwald's step rule. Four intermediate phases were identified, among them was Mg3Pd5, a previously unknown phase with a Ge3Rh5-type structure: space group Pbam, a=5.427(2), b=10.588(5), c=4.1304(12) A.

Zr6STe2 ist durch Reduktion eines Gemenges von ZrTe2 und ZrS2 mit Zirconium in gasdicht verschweisten Tantaltiegeln bei 1520 K zuganglich. Die raumlich gemittelte Kristallstruktur von Zr6STe2 lasst sich in der orthorhombischen Raumgruppe Cmcm beschreiben: a = 377.81(4), b = 1156.4(1), c = 887.96(8), Z = 2, Pearson-Symbol oC18, 320 Reflexe (I > 2σ(I)), 22 Variablen, Rw(I) = 0.088. Zr6STe2 bildet einen eigenen Strukturtyp, der sich struktursystematisch als teilweise aufgefullter Re3B-Typ einordnen lasst. Die Telluratome sind dreifach-uberdacht, verzerrt trigonal-prismatisch von neun Zirconiumatomen umgeben. Die Zr9Te-Tetrakaidekaeder sind uber gemeinsame trigonale Prismenflachen (langs [100]), Kanten (etwa parallel [001]) und Spitzen (langs [010]) zu einem dreidimensionalen Tetrakaidekaedernetzwerk [Zr9/3Te] verknupft, zu dessen Stabilitat homonukleare Zr–Zr-Bindungswechselwirkungen masgeblich beitragen. Zwischen den Tetrakaidekaedern befinden sich Zr6-Oktaeder, die uber Kanten (langs [100]) und Spitzen (langs [001]) zu Schichten verknupft sind. Infolge einer Verzerrung der Struktur weitet sich die Halfte der Oktaeder einer Schicht soweit auf, dass die Schwefelatome Platz darin finden. Den Beugungsbefunden nach erfolgt die Ausordnung der Leerstellen in benachbarten Oktaederschichten unabhangig voneinander. Zr6STe2 – a Zirconium-rich Sulfide Telluride with a Zr3Te Partial Structure of the Re3B Type Zr6STe2 is accessible through the reduction of a mixture of ZrTe2 and ZrS2 with zirconium in fused tantalum tubes at 1520 K. The spatially averaged crystal structure of Zr6STe2 is described in the space group Cmcm, a = 377.81(4), b = 1156.4(1), c = 887.96(8), Z = 2, Pearson symbol oC18, 320 reflexions (I > 2σ(I)), 22 variables, Rw(I) = 0.088. Zr6STe2 crystallizes in a unique structure type, which can be seen as a filled Re3B type structure. The tellurium atoms are surrounded by nine zirconium atoms situated at the vertices of a distorted, tricapped trigonal prism. The Zr9Te tetrakaidecahedra are connected by common triangular prism faces parallel [100], edges approximately along [001] and common vertices along [010], thus forming a three-dimensional tetrakaidecahedral network [Zr9/3Te], which is decisively stabilized by homonuclear Zr–Zr-interactions. The tetrakaidecahedra are arranged in such a way, that Zr6 octahedra occur. The octahedra are arranged into layers by sharing edges parallel [100] and vertices along [001]. As a result of a distortion of the structure, every second octahedron is expanded to such an extent as to be able to smoothly accommodate sulfur atoms. According to the modulation of the diffraction intensities, the vacancy ordering in adjacent layers of octahedra occurs independently of each other.

The phase relations between the palladium-rich phases of the gallium–palladium system are clarified by combining preparative methodologies with powder X-ray diffraction and thermochemical analyses. A modified phase diagram of the palladium-rich part of the system is presented. The structure of Ga 3 Pd 7 , decomposing peritectoidally at 881(2)°C, was determined by powder X-ray diffraction and refined by a Rietveld profile fit. Ga 3 Pd 7 adopts a new structure type with monoclinic space group symmetry: C2/m , Z =2, a =1359.46(2) pm, b =405.510(5) pm, c =544.339(6) pm, β =105.2219(7)°, wR P =0.082. The structure can be seen as a strongly distorted, ordered variant of a respective Ga x Pd 1− x fcc solid solution. It comprises two structural motifs: layers of columns of fused (GaPd 6/2 ) 2 prisms are formally separated by equiatomic GaPd layers. The impact of the composition on the structure of Co 2 Si-type Ga 1− x Pd 2+ x was studied. There exists a symmetry relation between the cubic close-packed arrangement of atoms and the structures of the Co 2 Si-type branch of AB 2 phases with Pearson symbol oP12 and space group symmetry Pnma .

The structure of a hexagonal approximant of the dodecagonal tantalum telluride dd-Ta 1.6 Te was studied by means of high resolution transmission electron microscopy and electron diffraction. A hierarchical building principle underlying the structures of two other approximants, Ta 97 Te 60 and Ta 181 Te 112 , was applied in order to deduce the crystal structure of the approximant with highest tellurium content, Ta 21 Te 13 .

A series of metal-rich tellurides in the ternary system Ta/V/Te crystallizes in closely related structures representing different arrangements of a basic disc-like (Ta, V) 151 Te 74 cluster. The centres of these clusters define various periodic or aperiodic square-triangle tilings on a length scale of about 2 nm. The structure of the approximant Ta 83 V 14 Te 60 with its underlying square tiling has been studied under various imaging conditions by high-resolution transmission electron microscopy and complementary image simulations. At a large defocus e-180 nm, a (Ta, V) 151 Te 74 cluster is represented by a bright dot surrounded by 12 others forming a dodecagon. The application of this selective imaging technique allows us to determine the tilings, i.e., the cluster arrangements, of new approximants and of quasicrystalline phases almost unambiguously. More complex contrast features as observed in some regions of the sample and the streaks turning up in reciprocal space are interpreted as stacking faults along the pseudo-12-fold axis.

Zr5Te6 has been synthesized and its structure determined by means of single crystal X-ray diffraction to be trigonal, P3m1, Z=3, Pearson symbol hP33, a = 1172.8(2) pm, c = 707.0(1) pm. Zr5Te6 adopts a metal-deficient, vacancy-ordered 3a x 3a x 1c superstructure of the NiAs type structure. In the Zr atom layers, alternately one and two out of nine Zr atoms are missing. The less densely populated layers (7/9) consist of star-shaped Zr7 clusters with intracluster contacts of 351.1 pm; the shortest Zr-Zr intercluster distance is 470.5 pm. In the more densely populated Zr atom layers (8/9), three quarters of the Zr atoms are arranged to pairs (326.4 pm). The distinctive distribution of the vacancies affords a topologically uniform fivefold Zr coordination (283.5 - 302.6 pm) for all three crystallographically inequivalent Te atoms. They are shifted towards the vacancies in the Zr atom layers. The associated corrugation of the Te atom layers is characterized by an amplitude of 28 pm. The Te-Te contacts are > or =368.1 pm. According to extended Huckel calculations, the defects in the Zr atom layers lead to a reduction in overall Zr-Te bonding interactions relative to ZrTe (NiAs). However, through the clustering the total attractive intralayer Zr-Zr interactions increase considerably, thus providing decisive stabilization of the structure. As revealed by thermal analyses, Zr5Te6 undergoes a reversible phase transition at 1,513 +/- 5 K. On the Zr-rich side, Zr5Te6 coexists with ZrTe (WC), and, above 1,438 +/- 5 K with the hitherto unknown ZrTe (MnP). Zr5Te6 exhibits temperature independent paramagnetic properties (chimol = 0.7 x 10(-3) cm3 mol(-1)) that are typical for a metallic conductor. An abrupt increase in the magnitude of the diamagnetic susceptibility below 2.2 K in a weak magnetic field indicates a superconducting transition.

Die Verbindung Ta6S1+xTe3–x ist durch Umsetzung eines entsprechenden Gemenges aus 2 H–Ta1.3S2, TaTe2 und Tantal in gasdicht verschweisten Tantaltiegeln bei 1273 K zuganglich. Die Ergebnisse der Einkristall-Rontgenstrukturanalyse einer Phase nahe der tellurreichen Grenze des Homogenitatsgebiets werden mitgeteilt. Ta6S1.00Te3.00(1) kristallisiert triklin, Raumgruppe P1, a = 993.14(8) pm, b = 1032.18(8) pm, c = 1378.78(11) pm, α = 79.32(1)°, β = 81.36(1)°, γ = 85.74(1)°, Z = 6, Pearson-Symbol aP60, 6048 Io > 2σ (Io), 286 Variablen, wR2 = 0.067. Der metallreichen Schichtstruktur von Ta6STe3 liegen zentrierte, ikosaedrische Ta13-Cluster und deltaedrische, von Chalkogenatomen erganzte Metallclusterfragmente bestehend aus 11, 12, 13, 14 und 16 Atomen zugrunde. Die Cluster durchdringen sich unter Segregation von Tantal und Chalkogen zu Schichtpaketen [Q–Ta3–Q]. Das besondere Merkmal der Struktur ist ein linsenformiger heptagonal-antiprismatischer Ta30-Cluster, der einem Fragment der pentagonal-antiprismatischen Kolumnarstruktur von Ta6S entspricht. Die Ta30-Cluster und verzerrt ikosaedrische Ta13-Cluster sind zu gewellten, tetraedrisch dicht gepackten Schichten verknupft und kondensiert. Die verbleibenden Valenzen der Tantalatome werden von den Chalkogenatomen abgesattigt, die ihrer oberflachenbedeckenden Funktion gemas einseitig von drei bis sechs Metallatomen umgeben sind. Ta6STe3 ist ein masiger metallischer Leiter (ρ293 K = 3 × 10–4 Ωcm) mit den dafur typischen, temperaturunabhangigen paramagnetischen Eigenschaften. The Metal-rich Layer Structure of Ta6STe3 Ta6S1+xTe3–x was prepared from an appropriate mixture of 2 H–Ta1.3S2, TaTe2, and Ta in a fused tantalum tube at 1273 K within 3 d. The results of a X-ray single crystal structure analysis for a phase near the Te-rich limit of the homogeneity range are reported. Ta6S1.00Te3.00(1) crystallizes in the triclinic space group P1, a = 993.14(8) pm, b = 1032.18(8) pm, c = 1378.78(11) pm, α = 79.32(1)°, β = 81.36(1)°, γ = 85.74(1)°, Z = 6, Pearson symbol aP60, 6048 Io > 2σ (Io), 286 variables, wR2 = 0.067. The metal-rich layer structure of Ta6STe3 comprises distorted icosahedral Ta13 clusters and related deltahedral cluster fragments complemented by chalcogen atoms. The centred clusters consist of 11, 12, 13, 14, or 16 atoms. They interpenetrate into lamellae in which the tantalum and chalcogen atoms are spatially segregated according to [Q–Ta3–Q]. The signature of the structure is a lenticular heptagonal antiprismatic Ta30 cluster which seems to be excised from the pentagonal antiprismatic columnar structure of Ta6S. The Ta30 clusters and distorted icosahedral Ta13 clusters are connected and fused into puckered layers. The rest of the tantalum valences are used for heteronuclear bonding. The chalcogen atoms having three to six next tantalum atoms coat the corrugated, tetrahedrally close-packed layers. Ta6STe3 is a moderate metallic conductor (ρ293 K = 3 × 10–4 Ωcm) exhibiting typical temperature independent paramagnetic properties.

Single crystals of WC type ZrTe were prepared from the elements. A single crystal structure determination of this structure type was performed for the first time: ZrTe (WC) crystallizes in the hexagonal space group P6̄m2 (No. 187), hP2, Z - 1, a - 377.06(5), c = 386.05(8) pm; 84 reflections, 5 variables, R(F) = 0.037. The distinctions in bonding for ZrTe (WC) and a hypothetical stoichiometric ZrTe crystallizing in the NiAs type structure were analyzed on the basis of extended Hückel calculations. Heteronuclear interactions contribute most strongly to the stability of both structures. Attractive Zr-Zr interactions energetically favour ZrTe (WC) relative to ZrTe (NiAs). The Fermi level of ZrTe (WC) resides in a local minimum of the DOS, whereas that of ZrTe (NiAs) intersects a local DOS maximum, and is pushed up by about 0.5 eV, expressing the decisive destabilization of NiAs type ZrTe. As a consequence, metal deficiency is observed for ZrTe (NiAs), in contrast to ZrTe (WC).

Two-layered tantalum chalcogenides are evaluated as alkali metal intercalation hosts in lithium and sodium electrochemical cells. The metal-rich pseudo-two-dimensional solid Ta 2 Se shows a poor intercalation behaviour. Lithium reacts with the selenide by deintercalating selenium from the blocks of Ta-related b.c.c. structure leading to a collapse of the structure and the formation of tantalum metal. Sodium is reversibly intercalated to a limited extent leading to complex structural changes in the selenide, as revealed by electron diffraction. The two-dimensional telluride Ta 2 Te 3 allows a topotactic intercalation of lithium below 1 F/mol, while a more extended reaction leads to sample amorphization. The better intercalation behaviour of this solid can be related with the one-atom thick metal layer and the van der Waals gap separating tellurium atoms of successive layers. Sodium can be reversibly intercalated into Ta 2 Te 3 in sodium cells which show a good cycling behaviour. Exposure of the intercalated solid to water vapour allows the preparation of hydrated products with a monolayer or a bilayer of water molecules solvating sodium in the interlayer space.

Die gemischtvalenten Oxide Sr1.85Ta15O32 (1), Ba1.88Ta15O32 (2), K2Ta15O32 (3), Rb2Ta15O32 (4) wurden durch Umsetzung von Ta2O5 mit Tantal und den entsprechenden Carbonaten bei 1520–1670 K in gasdicht verschweisten Tantaltiegeln erhalten. Rontgen-Einkristallstrukturanalysen zufolge kristallisieren die Verbindungen in der Raumgruppe R3¯ mit den Gitterparametern 1: a = 777.36(11), c = 3516.2(7) pm; 2: a = 778.87(11), c = 3548.1(7) pm; 3: a = 780.7(2), c = 3573.1(11) pm; 4: a = 781.90(11), c = 3593.0(7) pm. In einer defekten, dichten Packung von Oxidionen der Schichtabfolge chhhh sind antikuboktaedrische Lucken von den Alkalimetallkationen vollstandig, von den Erdalkalimetallkationen, die zusatzlich lagefehlgeordnet sind, zu 92 bis 94% besetzt. Kleinere Lucken befinden sich in den Zentren von kuboktaedrischen Ta6O12-Clustern, den charakteristischen Baugruppen dieser niedervalenten Oxotantalate. Abweichend von der energetisch gunstigen Elektronenzahl 14 stehen den Clustern in den Alkalimetall- 13 und in den Erdalkalimetallverbindungen nahezu 15 Elektronen fur die Bildung homonuklearer Ta–Ta-Bindungen zur Verfugung. Die Unterschiede in der Valenzelektronenkonzentration machen sich auch im Ta–O-Abstandsspektrum und den Ta–Ta-Abstanden der Ta3O13-Oktaedertripel, einer weiteren typischen Baugruppe dieser Oxide, bemerkbar. Die Abstandsvariationen lassen sich auf Unterschiede im lokalen Ladungsausgleich durch die ein- bzw. zweiwertigen Kationen zuruckfuhren. Die Oxide 2, 3 sind Halbleiter mit Bandlucken im Bereich von 130 bis 360 meV. Tantalum Cluster in an Oxidic Matrix – Synthesis and Structures of Mixed-Valence Oxotantalates M2–δTa15O32 (M = K, Rb (δ = 0); M = Sr (δ = 0.15), Ba (δ = 0.12)) The mixed-valent oxides Sr1.85Ta15O32 (1), Ba1.88Ta15O32 (2), K2Ta15O32 (3), Rb2Ta15O32 (4) were prepared from appropriate mixtures of Ta2O5, tantalum and the corresponding carbonate at 1520–1670 K in sealed tantalum tubes. According to X-ray single crystal structure analyses the oxides crystallize in the space group R3¯, Z = 1. The lattice parameters in the hexagonal setting are a = 777.36(11), c = 3516.2(7) pm for 1, a = 778.87(11), c = 3548.1(7) pm for 2, a = 780.7(2), c = 3573.1(11) pm for 3, and a = 781.90(11), c = 3593.0(7) pm for 4. The oxide ions form a defect dense packing with the layer sequence chhhh. Anti-cuboctahedral sites are completely occupied by the alkali metal cations. The alkaline earth cations occupy 92 to 94% of such sites; they are displaced from the centres. Smaller voids are located in the centres of the cuboctahedral Ta6O12 clusters forming the characteristic structural unit of these low-valent oxotantalates. In case of 3 and 4 the clusters have 13 electrons, in case of 1 and 2 they have close to 15 electrons available for Ta–Ta-bonding. Moreover, the structures of the alkali and alkaline earth metal compounds differ notably with respect to the spectrum of Ta–O and Ta–Ta distances in the Ta3O13 octahedra triples forming another characteristic structural unit for these oxides. Such differences are traced back to distinct local charge balances for the uni- and divalent cations. The oxides 2, 3 are semiconductors with band gaps ranging from 130 to 360 meV.

AuTa5S was prepared from a compressed mixture of tantalum disulfide, tantalum, and gold in a sealed tantalum capsule at 1650 K within 2 days. Above 1750 K the sulfide disproportionates in the solid state. The structure of AuTa5S (a=1250.82(3) pm,F 4 3m,Z=16, Pearson symbolcF112) was determined from integrated X-ray powder diffraction intensities by direct methods and subsequently refined by fitting the profiles (13 structure variables,Rwp=0.036). Three of five crystallographically distinct metal atoms have distorted icosahedral coordinations. Sulfur is trigonal antiprismatically coordinated by tantalum. The structure is composed of two mutually interpenetrating zinc blende-like frameworks consisting of corner-connected STa6octahedra and corner-connected Au4Ta4and Ta4Ta4stellae quadrangulae. The unique structure of AuTa5S represents a link between two major intermetallic structure families, theη-carbide-type and the Mn23Th6-type structures.

Beugungsbilder mit zwolfzahliger Rotationssymmetrie (siehe rechts) liefert das erste quasikristalline Chalkogenid, das durch Reduktion von TaTe2 mit Tantal unterhalb von 1870 K im praparativen Masstab zuganglich ist. Als erste allen Befunden nach stabile dodekagonale Phase eroffnet das tantalreiche Tellurid Ta1.6Te die Moglichkeit, diesen eigenartigen Ordnungszustand eingehend zu untersuchen.

Hf 2 Te was prepared by arc-melting appropriate compressed mixtures of HfTe 2 and hafnium. The structure of the new hafnium-rich telluride was determined by means of powder diffractometry, R B =0.0565. Hf 2 Te adopts a Nb 2 Se-type structure, monoclinic, space group C2/m, Z=8 , Pearson symbol mS24, a =1516.3(2) pm, b =370.26(4) pm, c =1006.4(1) pm, β=90.50(1)°. The structure comprises pairwise interpenetrating columns of trans-face-shared centred Hf 9 cuboids. The columns form puckered slabs which are interconnected by homo- and heteronuclear bonds. Tellurium atoms are one-sidedly coordinated by six hafnium atoms. The coordination configurations about the two distinct tellurium atoms represent Hf 6 Te hypho-fragments of a tri-capped trigonal prismatic Hf 9 Te closo-cluster. Characteristic features of four other M 2 Q structure types are elucidated. The valence electron concentration available for metal-metal bonding together with the cohesive energy of the respective metal are found to control the formation of the various M 2 Q metal partial structures.