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Structure and chemical composition of intermetallic phases in unmodified and Sr-modified Al-10Si-0.3Fe casting alloys based on pure elements are identified by transmission electron microscopy and energy-dispersive X-ray spectroscopy. A three-dimensional characterization of intermetallic phases is performed by focused ion beam tomography. Both alloys were found to contain Fe-rich α-Al 14 Fe 3 Si 2 with a bcc structure and the τ 2 phase Al 4.5 FeSi, also called γ phase AlFeSi and both exhibit the “Chinese script” morphology in two dimensions, appearing as complex shaped objects in three dimension visualizations. The crystal structure of the τ 2 phase is shown to be trigonal R -centred rather than monoclinic as claimed by all published studies. It is related to the structure of R phases such as Mn 85.5 Si 14.5 . In the Sr-modified alloy, the tetragonal δ-Al 4 FeSi 2 phase is observed, which appears as thin platelets in 3D. No monoclinic β-Al 5 FeSi phase is found in any of the alloys unlike in industrial alloys that contain further impurities (Mn, Cr, Cu, P). Thus, the common β-phase is not a feature of the pure Al-Si-Fe system. In summary, addition of the modifier strontium to Al-10Si-0.3Fe alloys containing no further alloying elements markedly promotes the formation of δ-Al 4 FeSi 2 , but suppresses the formation of α-Al 14 Fe 3 Si 2 , whereas τ 2 phase Al 4.5 FeSi is found in similar fractions in both alloys.

Co–Re–Cr-based alloys with additions of 200 ppm or 1000 ppm boron were investigated by high-resolution methods such as scanning electron microscopy, transmission electron microscopy and three-dimensional atom probe. The chemical composition of borides with a lamellar structure resembling a eutectic as determined by three-dimensional atom probe is Cr 0.68 Re 0.46 Co 0.24 B, the composition of isolated boride particles at the grain boundaries is Cr 0.76 Re 0.40 Co 0.35 B. A systematic study was carried out to determine the crystal structure of the various types of borides. Despite their varying chemical composition, the borides in the two alloys, even when appearing in different morphologies, exhibit the same orthorhombic C -centred unit cell with lattice parameters a = 0.436 nm, b = 0.755 nm and c = 1.498 nm.

Ab initio molecular dynamic simulations and high-temperature synchrotron crystallography show that β-Si(NCN)2 exhibits isotropic negative thermal expansion from 500 to 1123 K over its entire temperature stability range. The experimental value of the linear expansion coefficient changes from α = −1.24 × 10–6 K–1 at 500 K to α = −1.93 × 10–6 K–1 at 1123 K. Examination of vibrational motions locate the effect to transverse vibrations of carbodiimide fragments bridging between Si atoms (Si–N═C═N–Si). A detailed atomistic analysis reveals that the roto-vibrational movements of the bridging NCN units resemble that of a centrifugal governor pulling together the crystal framework upon temperature increase.

The efficient green phosphor Ba(3)Si(6)O(12)N(2):Eu(2+) and its solid-solution series Ba(3-x)Sr(x)Si(6)O(12)N(2) (with x approximately = 0.4 and 1) were synthesized in a radio-frequency furnace under nitrogen atmosphere at temperatures up to 1425 degrees C. The crystal structure (Ba(3)Si(6)O(12)N(2), space group P3 (no. 147), a = 7.5218(1), c = 6.4684(1) A, wR2 = 0.048, Z = 1) has been solved and refined on the basis of both single-crystal and powder X-ray diffraction data. Ba(3)Si(6)O(12)N(2):Eu(2+) is a layer-like oxonitridosilicate and consists of vertex-sharing SiO(3)N-tetrahedra forming 6er- and 4er-rings as fundamental building units (FBU). The nitrogen atoms are connected to three silicon atoms (N3), while the oxygen atoms are either terminally bound (O1) or bridge two silicon atoms (O2) (numbers in superscripted square brackets after atoms indicate the coordination number of the atom in question). Two crystallographically independent Ba(2+) sites are situated between the silicate layers. Luminescence investigations have shown that Ba(3)Si(6)O(12)N(2):Eu(2+) exhibits excellent luminescence properties (emission maximum at approximately 527 nm, full width at half maximum (FWHM) of approximately 65 nm, low thermal quenching), which provides potential for industrial application in phosphor-converted light-emitting diodes (pc-LEDs). In-situ high-pressure and high-temperature investigations with synchrotron X-ray diffraction indicate decomposition of Ba(3)Si(6)O(12)N(2) under these conditions. The band gap of Ba(3)Si(6)O(12)N(2):Eu(2+) was measured to be 7.05+/-0.25 eV by means of X-ray emission spectroscopy (XES) and X-ray absorption near edge spectroscopy (XANES). This agrees well with calculated band gap of 6.93 eV using the mBJ-GGA potential. Bonding to the Ba atoms is highly ionic with only the 4p(3/2) orbitals participating in covalent bonds. The valence band consists primarily of N and O p states and the conduction band contains primarily Ba d and f states with a small contribution from the N and O p states.

Among binary compounds, there is a high potential for discovery of novel members (polymorphic phases or compounds) of the nitrides of transition metals group due to a pronounced dependence of the oxidation state of the metals (M) on pressure. The power of high pressure–high temperature (HP-HT) route for synthesis of binary nitrides has already been demonstrated by the discovery of cubic nitrides of the group 4 and 14 elements, of crystalline polymorphs of P3N5, and by reports on formation of four noble metal nitrides. It is anticipated that such HP products exhibit, in addition to enhanced elastic and mechanical behavior, other functional properties making them interesting for industrial applications. Here, HP–HT synthesis research is extended to nitrides of group 5 elements, resulting in the discovery of a novel hard tantalum nitride, exhibiting U2S3 structure: η-Ta2N3 (Pbnm, a = 8.1911(17) A, b = 8.1830(17) A, c = 2.9823(3) A). The stoichiometry is supported by two independent means, verifying that η-Ta2N3 is the first thermodynamically stable transition metal nitride with a N:M ratio exceeding 4:3. Due to its high hardness and peculiar texture (needle-like and granular crystallites), η-Ta2N3 may find practical applications as a hard fracture resistant material.

This paper presents our recent results on synthesis and properties of high-pressure cubic zirconium(IV)- and hafnium(IV) nitrides having Th3P4-type structure, c-M3N4 (M = Zr or Hf). c-M3N4 were first synthesized in microscopic amounts in a laser-heated diamond anvil cell (LH-DAC) at pressures above 15 GPa and temperatures above 2500 K. Further, macroscopic amounts of c-Hf3N4 and of a new oxygen-bearing zirconium nitride, c-Zr2.86(N0.88O0.12)4, were synthesized at 12 GPa and about 1900 K using a multi-anvil apparatus. The lattice parameter of c-Hf3N4 was determined to be a0 = 670.2(1) pm. The a0 of c-Zr2.86(N0.88O0.12)4 of 675.49(1) pm was found to be slightly larger than that of c-Zr3N4 (674.0(6) pm). The bulk moduli, B0, of 219 GPa for c-Zr2.86(N0.88O0.12)4 and of 227 GPa for c-Hf3N4 were obtained from compression measurements. Combining the compression and indentation data we determined for c-Zr2.86(N0.88O0.12)4 its isotropic shear modulus G0 = 96 GPa. Finally, Vickers microhardness, indentation fracture toughness and thermal expansion of c-Zr2.86(N0.88O0.12)4 were measured.

Sol−gel processing via the modified nonalkoxide route resulted in the formation of nanocrystals of the corundum-type In2O3 polymorph, which revealed characteristic rhombohedra with a morphology very close to cubes. Because the cubic bixbyite-type In2O3 polymorph is more abundant under ambient conditions, the seemingly cube-shaped morphology might confuse the experimentalist. As shown by transmission electron microscopy, this morphology does not reflect any relation to a cubic structure but appears accidentally with form {012} at a specific axis ratio of corundum-type structures. The pseudocubic particles have also been reported for α-Fe2O3, also in this case the pseudocubic nanorhombohedra are terminated by {012} facets.

Abstact A new phase in the system Sc–Re–O, ScRe 2 O 6 , was synthesized for the first time in sealed silica tubes and its crystal structure was solved by single crystal X-ray diffraction. ScRe 2 O 6 (space group P 2 1 / a , a =5.6176(9) A, b =4.7970(9) A, c =7.5143(16) A, β =97.49(2)°, Z =2) crystallizes in a new rutile-type structure, derived from three formula units by splitting the cation site in ratio 1:2. Re 2 O 10 clusters can be considered as structural units, in which the rhenium ions form pairs by metallic bonds with a Re–Re distance of 2.523(3) A. No phase transition was observed in the temperature range of 295–930 K. The compound has a metallic character of conductivity in the temperature range of at least 4–950 K and displays a ferromagnetic ordering above room temperature (“unconventional Re-magnetism”).

The present article reviews recent advances in synthesis of novel phases in the ternary Si-C-N system. A dense carbon nitride phase, C 2 N 2 (NH), was synthesized for the first time at high pressures and high temperatures in a laser heated diamond anvil cell (LH-DAC). Based on results of electron diffraction, EELS- and SIMS-measurements combined with theoretical calculations the structure of this new C-N-H compound was analysed to be a defect wurtzite structure of the sinoite (Si 2 N 2 O)-type. Farther, a variety of amorphous SiCN phases and the first ternary crystalline phases, namely Si(NCN) 2 and Si 2 N 2 (NCN), were synthesized at ambient pressure. In general, the high-pressure polymorphs of Si-C-N materials are predicted to exhibit a unique combination of high hardness, thermal stability and oxidation resistance with interesting optoelectronic properties.

(Figure Presented) Extreme chemistry: The carbon nitride imide C 2 N 2 (NH) is synthesized from the single-source precursor 1-cyanoguanidine under high-pressure and high-temperature conditions in a laser-heated diamond-anvil cell. Characterization of single crystals recovered at ambient conditions reveals that the new compound adopts a defect wurtzite structure (see picture). © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

The hydrogenation of dienes such as 1,3-butadiene, cyclooctadiene, and of acetylenic hydrocarbons on Pd catalysts shows high reaction rates and consequently, a strong influence of mass transfer on the selectivity of the intermediate alkene or cycloalkene product. 100 % selectivity towards (cyclo)-alkene hydrogenation is achieved for the gas phase when the Thiele modulus is equation image, where L is the thickness of the active layer and Deff is the effective diffusion coefficient of the diene. The interdependencies expressed by this formula were studied in detail using model catalysts with regular pores of uniform length and diameter and perpendicular to the surface. These catalysts were prepared by anodic oxidation of aluminium wires and immobilization of the active Pd. For the liquid phase procedure of selective hydrogenation, a reaction mass transfer model has been derived in order to compare the gas phase and liquid phase procedures, in particular with respect to the selectivity. The hydrogenation of 1,3-cyclooctadiene and of 1,3-butadiene were studied for both procedures employing the same catalyst. The rate of hydrogenation can be represented for both cases by the identical kinetic equation r1 = k1 cH2. This result is interpreted by assuming that the access of hydrogen to the surface through the dense layer of adsorbed diene is the rate determining step.

The controlled fabrication of poly- and single-crystalline Au nanowires is reported. In polycarbonate templates, prepared by heavy-ion irradiation and subsequent etching, Au nanowires with diameters down to 25 nm are electrochemically synthesized. Four-circle X-ray diffraction and transmission electron microscopy measurements demonstrate that wires deposited potentiostatically at a voltage of -1.2 V at 65 °C are single-crystalline and oriented along the [110] direction. By reverse-pulse electrodeposition, wires oriented along the [100] direction are grown. The wires are cylindrical over their whole length. The morphology of the caps growing on top of poly- and single-crystalline wires is a strong indication of the particular crystalline structure of the nanowires.

Nanocrystalline Sm2O3 and Sm2O3–MgO powders have been prepared by spray pyrolysis of aqueous precursor solutions containing citric acid as a complexant. Synthesized powders consist of hollow spheres with thin shells. The two-phase samples exhibit an improved microstructural stability compared with pure Sm2O3. The microstructure before and after various heat treatments has been investigated by high-resolution transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, and X-ray diffraction.

By the substitution of one methyl group in Neopentane C(CH3)4 with a methylchlorid group the globular sphere is expanded in 1-chloro-2,2-dimethylpropane (CH3)3C(CH2Cl). With the aid of DSC measurements, X-ray powder diffraction, 1H NMR and 35Cl NQR measurements two orientationally disordered (plastic) phases were established. The low temperature structure was solved and a structural model of phase II is proposed. A mechanism to describe the reorientation in the different phases is given as well as a connectivity scheme between the phases is discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The mixed valence compound Fe2+5Fe3+2SiO10, informally known as “iscorite”, has been investigated by high-resolution and analytical transmission electron microscopy (HRTEM & ATEM) including energy-dispersive X-ray microanalysis (EDX) and electron energy-loss spectroscopy (EELS). EDX and EELS measurements confirm the chemical composition of the investigated sample yielding concentration ratios of Fe/Si = 7.1 and Fe3+/ΣFe = 0.29 ± 0.03 which resemble the expected ratios of Fe:Si = 7:1 and Fe3+/ΣFe = 2:7. The lattice parameters of the monoclinic cell given by Smuts et al. (1969) and Modaressi et al. (1985) were confirmed: a = 2.1336 nm, b = 0.30679 nm, c = 0.58744 nm, β = 98.06°. However, space group I 12/ m 1 (No.12) was found instead of the published space group P 121/ m 1 (No.11). In selected area electron diffraction (SAED) patterns in the orientation [011], streaking of the basic reflections and diffuse diffraction lines located at 1/2 (b* + c*) parallel to the aa direction are observed indicating an intense microstructural disorder. For the first time, we report the occurrence of twins on (200) in “iscorite”. These structural modulations observed in SAED patterns and in Fourier-filtering analysis of the HRTEM images result from Fe3+/Si-disorder on tetrahedral sites and Fe2+/Fe3+-disorder on octahedral sites. Therefore, the crystal structure of “iscorite” has been described anew within the non-standard centrosymmetric space group I 12/ m 1 by the use of the single-crystal X-ray diffraction (XRD) data of (Modaressi et al. , 1985) in combination with our SAED and HRTEM results.

This paper presents current developments in pearl luster pigments. After a short introduction on the application of pigments, the synthesis and characterization of a ZrO 2 / SiO 2 based pearlescent pigment will be described. The applied methods for characterization were ex situ x-ray diffraction (XRD) of dried and calcined pigment powders, in situ XRD in a temperature range from 100°C up to 850 °C and transmission electron microscopy (TEM) of thin cross-sections. The XRD measurements were used for phase analysis, determination of cell parameters and average crystal grain sizes. A special preparation method was developed for TEM cross section specimens for platy like pigment particles. The microstructure, the interface between substrate and coating material and the particle sizes are described with high resolution TEM pictures of cross section specimens. The basic interest is the behaviour of the zirconium dioxide coating during sintering in order to achieve a condensation of the film without any further crystal grain growth.

Extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) studies on supported bimetallic Pt/Pd diesel oxidation catalyst (Pt:Pd weight ratio 2:1) after various treatments were compared with those of monometallic Pd and Pt catalysts prepared under similar conditions. After calcination and thermal ageing, the coexistence of alloyed bimetallic Pt/Pd particles and of tetragonal PdO has been found in the bimetallic Pt/Pd catalyst. PdO is present in form of crystals at the surface of the Pt/Pd particles or as isolated PdO crystals on the support oxide. Bimetallic Pt/Pd nanoparticles were already formed in the Pt/Pd catalyst after calcination. Hydrogen treatment causes the formation of randomly alloyed Pt/Pd nanoparticles. In the thermally aged catalyst, a strong indication for an enrichment of Pt in the interior of the particle and of Pd at its outer shell was found. In the monometallic catalyst, the Pd is found to be completely oxidised already after calcination and to consist of metallic Pd in zero-valent state exclusively after reductive treatment. Ageing under hydrothermal oxidative atmosphere leads to complete oxidation of the Pd species. After calcinations, the catalytic activity of the Pt/Pd catalyst studied is comparable to those of monometallic Pt catalysts. In contrast to monometallic Pt catalysts, the alloyed system show significant stabilisation against sintering and a much higher activity after the thermal ageing step. This stabilisation of dispersion and the presence of Pt atoms on the surface of the Pt/Pd particles are considered to cause the higher catalytic activity of metallic particles for the oxidation of carbon monoxide and propene after ageing.

Poly- and single-crystalline Bi nanowires are fabricated by electrochemical deposition in etched ion-track membranes. Two deposition parameters, voltage and temperature, strongly influence the nanowires' morphology and texture. X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveal that potentiostatically deposited nanowires are textured, the texture increasing for wires deposited at higher temperatures and smaller overpotentials. At T = 60 °C and low overpotentials, single-crystalline wires are produced. Wires deposited with reverse pulses exhibit a texture, which is more pronounced for shorter cathodic cycles and higher anodic voltages. They consist of several crystals of size at least .

The roughening of interfaces as a function of layer thickness and magneto transport properties have been investigated on sputter-deposited Fe/Ni 75 B 25 multilayer films. X-ray reflectivity data were recorded for Ni 75 B 25 (72 nm) film and for [Fe(2 nm)/Ni 75 B 25 (2 nm)] 16 and [Fe(4 nm)/Ni 75 B 25 (4 nm)] 8 multilayer films. A power law dependence of the interfacial width of growing Fe/Ni 75 B 25 interfaces was observed. The resulting growth exponents β were found to be in the range of 0.55–0.58 in the initial growth stage of the multilayer with lower Fe/Ni 75 B 25 repetition thickness and at approximately 0.34 for multilayer with higher repetition thickness. The growth exponents were compared with theoretical calculations. High resolution electron microscopy revealed the columnar growth of the Fe/Ni 75 B 25 multilayer. Additionally, an increase of magnetoresistance was observed by the multilayering of Ni 75 B 25 films with Fe interlayers.

RbSn2F5 is a two-dimensional fluoride ion conductor. It undergoes a first-order phase transition to a superionic state at 368 K. The structure of the low temperature phase has been determined from the Rietveld analysis of the X-ray powder diffraction. The dynamic properties of the fluoride ions in RbSn2F5 have been studied by impedance spectroscopy and solid state NMR. The dc ionic conductivity of this sample shows an abrupt increase at the phase transition temperature. We have obtained the hopping frequency and the concentration of the charge carriers (F- ions) at different temperatures from the analysis of the conductivity spectra using Almond-West formalism. The estimated values of the charge carriers’ concentration agree well with that determined from the structure and were found to be independent of temperature. The relatively small value of the power-law exponent, $n \approx 0.55$ , supports the two-dimensional property of the investigated material. Furthermore, 19F NMR with simulation has suggested the diffusive motions of the fluoride ions between different sites. In contrast, 119Sn and 87Rb NMR spectra below 250 K supported the intrinsic disordered nature due to the random distribution of the fluoride ion vacancies.

Annealing of the (1.1 nm Co90Fe10/2.2 nm Cu)×20 and (1.1 nm Co90Fe10/2.2 nm Cu85Ag10Au5)×20 multilayers at 235 °C improved their magnetoresistance as compared to the virgin samples. Annealing at higher temperatures resulted in degradation of the magnetoresistance effect. This observation raised the motivation of a detailed structural study using small-angle X-ray scattering, wide-angle X-ray diffraction, electron diffraction and transmission electron microscopy with the aim to link the structural changes in the system to the changes in the magnetoresistance. The structure studies have shown that the maximum of the magnetoresistance observed after annealing at 235 °C is related to the separation of Co90Fe10 and Cu, which are partly intermixed at interfaces after the deposition process. The decay of the GMR effect at higher annealing temperatures is caused by an increase of the interface roughness, which led in the Co90Fe10/Cu multilayers to occurrence of non-continuous interfaces and to short-circuiting of magnetic layers. In the Cu85Ag10Au5 multilayers, the combination of small-angle X-ray scattering and wide-angle X-ray diffraction has shown that Cu85Ag10Au5 did not form an alloy with the nominal composition: Only a part of Au and Ag was dissolved in the copper structure; the remainder of Ag and Au formed precipitates.

The crystal structure of yttrium rhenium oxide, Y7ReO14−δ, is a 2×2×2 superstructure of the CaF2 structure, space group Fm 3 m , a=10.4770(14) A. The 32 cations within the unit cell are distributed with yttrium on the (4a)- and (24d)-sites and with rhenium on the (4b)-site. The 64 oxygen atoms occupy two (32f) sites (x,x,x), O(1) with x1=0.1351(9) and O(2) with x2=0.6054(11), in the undistorted fluorite structure x=0.125 and 0.625. The site occupation factor for the O(2) site is only 77(8)% in agreement with the maximum of 75% for δ=0 in the proposed stoichiometry. The electrical DC conductivity, measured on a single crystal, reveals semiconducting behavior between 165 and 265 K with a band gap of 157.4 meV.

The formation of carbon nanotubes via explosive decomposition of an energetic precursor, 2,4,6-triazido-s-triazine C3N12, was investigated with respect to the presence of the transition metals Fe, Ni, Cu, Ti and the degree of confinement of the explosive charge. The carbonaceous detonation products were characterized by transmission and scanning electron microscopy, energy dispersive X-ray analysis and infrared absorption spectroscopy. Multi-walled carbon nanotubes with diameters from 50 to 150 nm and a variety of morphologies were found. Metal particles in the tubes and at some of the tube ends indicate a catalytic growth mechanism.

We report on an optimized growth interruption time under an As flux during the AlSb/ InAs interface growth of unintentionally doped InAs quantum well structures. The migration-enhanced epitaxy method is used to create InSb interface bonds. After the deposition of the first In monolayer the surface is exposed to an As flux for different time periods, before the In shutter is opened again. Time-resolved reflection high-electron-energy diffraction (RHEED) and high-resolution transmission electron microscopy are used to characterize the interface. In combination with Hall measurements of single quantum well structures the interruption time is optimized. The interface quality depends on the RHEED intensity recovering during the interruption time under an As flux. If the interruption time is sufficient to reach the same RHEED intensity level as it is for the InAs growth, the electron mobility rises from 180,000 to 255,OOOcm 2 /Vs at 77 K. Furthermore, we observed that a disordered surface during the interface growth can be incorporated into the layer, leading to amorphous regions directly above the interface. Moreover, the disordering depends on the crystal orientation and is larger in the [III:0] azimuth.

A well-ordered simple icosahedral quasicrystalline phase has been found in the Zn-Mg-Er system. The structure of a splat-cooled and annealed sample was investigated by electron and X-ray powder diffraction. A quasilattice constant of 0.513nm was determined by the Elser method.

Representative samples of the two fabric varieties of microcrystalline quartz, chalcedony and quartzine, from agates of different origin were investigated by transmission electron microscopy (TEM). Both varieties contain lamellar admixtures of the SiO2 mineral moganite. The transitions from quartz to moganite within the fabric differ in a characteristic way. Whereas in quartzine the gradient between the structures is steep, the transition is more continuous in chalcedony. The morphology of moganite in chalcedony and quartzine is determined by the (101)-face; in pure moganite from Gran Canaria it is governed by the (110)-face.

Heat flow to [Fe(bzimpy)2](ClO4)2⋅0.25H2O complex (bzimpy=2,6-bis(benzimidazol-2-yl)pyridine) (I) was measured between 300 and 460 K by differential scanning calorimetry. This exhibits a well-developed peak characteristic of the first-order phase transitions at temperature 403 K. The enthalpy and entropy of transition from low-spin to high-spin state has been determined to be ΔH=17 kJ mol−1 and ΔS=43.0 Jmol−1 K−1. Heat flow to [Fe(bzimpy−1H)2]⋅H2O complex (bzimpy −1H=deprotonated bzimpy) (II) was measured between 300 and 580 K. The spin crossover in this system is accompanied with liberation of crystal water on the first heating. To monitor the structural changes during the spin crossover, powder diffraction data have been collected as a function of temperature.

Trirheniumdecaoxide, Re3O10, was obtained by the reaction of ReO2 and ReO3 in an arc-melting furnace. X-ray powder diffraction revealed a tetragonal structure with space group I4m2 and lattice constants a=5.171(1) and c=13.371(6) A. The crystal structure is built up by layers of corner-sharing [ReO5] square pyramids perpendicular to [001] with the apical oxygen pointing up and down alternatingly. These layers are interconnected by disordered [ReO6] octahedra. Early reports on Re2O5 are reviewed in the light of our results.

The crystal structure of a cubic phase in the system Zn-Mg-Er has been solved by a combination of high-resolution electron microscopy and X-ray powder diffraction. This phase is considered to be related to that of the quasicrystalline phase. The structure consists of 448 atoms in the unit cell with lattice constant of a 0 = 20.20A and the space group is F43m. Important structural elements in the cubic structure are interpenetrating icosahedral units around Zn and Mg atoms and Frank-Kasper polyhedra around the Mg atoms. No giant icosahedral atomic cluster, such as the 136-atom Bergman cluster, was found in the stucture.

The nature of a new zeolite overgrowth has been characterized. Two overgrown samples were studied. Each sample was made up of the phases faujasite and EMT. By Rietveld refinement of the powder patterns the structure of both phases including the distribution of cations in the overgrowth was determined as well as the weight fractions of the phases in both samples. The growth of FAU crystals on the surface of EMT crystals is epitactic, as shown by HRSEM images. The epitaxial relation is [111] FAU //[001] EMT , (-110) FAU //(110) EMT . The true atomic interfacial model of the interface between faujasite and EMT is still subject of further studies.

The space group of a cubic phase of Zn63Mg23Er14 has been determined to be F4̅3m by convergent-beam electron diffraction (CBED). This space group is in agreement with that assumed by X-ray structure analysis (Sterzel et al., Philos. Mag. Lett. 80 (2000) 239-247). A rhombohedral phase, which is considered as a superlattice ordered phase of the cubic phase, was found. The space group of the rhombohedral phase has been determined to be R3m by the CBED method.

Icosahedral phases in Zn-Mg-RE(RE=Er, Y) alloys have been studied by high resolution transmission electron microscopy (HRTEM) and electron diffraction for different RE contents. From the electron diffraction patterns along the twofold axis, for Zn60Mg30+xY10−x a face centered icosahedral structure was found with x=0 whereas crystals with x in the range of 4 display a simple icosahedral structure. In the system with RE=Er a cubic approximant of the icosahedral quasicrystalline phase, the so-called ‘R-phase’, was found. The R-phase crystallizes in the space group F 4 3m with a0=2.02 nm. The close relation between the R-phase and the icosahedral quasicrystal is shown by HRTEM imaging.

NaNO3, Synchrotron X-ray diffraction at 100 K: λ = 0.56Å, R-3c, a = 5.0655(5) Å, c = 16.577(3) Å, V = 368.4 Å3, Z = 6, F(000) = 78e, refinement on |F|. Anharmonic motion of N and O up to the fourth order of a Gram-Charlier expansion and multipoles for all ions were refined. R = 0.029, w R = 0.028, S 2 = 3.539, 369 unique intensities, 41 parameters. Neutron diffraction at 120 K: λ = 0.87 Å, R-3c, a = 5.0660(5) Å, c = 16.593(3) Å, V = 368.8 Å3, Z = 6, F(000) = 182.1 fm. Two data sets from two crystals of different sizes have been used, one with 187, the other with 165 unique intensities. Refinement on |F|2 including weak and negative intensities. Anharmonic motion of N and O up to the fourth order of a Gram-Charlier expansion was refined R = 0.112, w R = 0.080, S 2 = 3.499, 205 unique intensities, 35 parameters. Neutron diffraction at 563 K: λ = 0.92 Å, R-3m, a = 5.0889 (5) Å, c = 8.868(3) Å, V = 204.6 Å3, Z = 3, F(000) = 91.05e, refinement on |F|2 including weak and negative intensities. R = 0.031, w R = 0.017, S 2 = 1.714, 84 unique intensities, 16 refined parameters. At 100 K multipolar expansion of the electron density reveals bonding electrons and a strong deformation of the atoms within the planar NO3-group much clearer than at room temperature. At 563 K strongly anharmonic thermal displacement factors are found.

The third known polymorph of silicon nitride, which is cubic and was only recently discovered, has been prepared from two further, different precursors—Si2N2(NH) and a-Si3N4—in a high-pressure, high-temperature synthesis using multi-anvil presses. The synthesis and characterization of the products is described, which included a structural determination by Rietveld refinement of powder X-ray diffraction data. Spinel-type c-Si3N4 is significantly harder than the α and β phases and may possibly find applications as an ultrahard material.

A cubic approximant for the icosahedral phase is found in the Zn-Mg-Er system. The preparation of the Zn-Mg-Er ternary phase (the so-called R phase) through quenching and annealing is described in detail. The R phase was found by means of scanning electron microscopy in combination with wavelength-dispersive X-ray analysis. The composition of the R phase varies around Zn63Mg23Er14 in different samples depending on the initial composition. The structure has been studied by a combination of high-resolution transmission electron microscopy (HRTEM) and X-ray powder diffraction. The R phase is cubic with a 0 = 2.02 nm and crystallizes in the space group F 43m. The close relationship of this phase to the icosahedral phase in the Zn-Mg-Y, RE system (RE = rare earth) is demonstrated through electron diffraction features and HRTEM images.

Compounds of the series Ln6ReO12, Ln=Ho, Er, Tm, Yb, and Lu, have been prepared by subsolidus reaction and are isotypic with Ln6MoO12, Ln6WO12, and Ln6UO12, crystallizing in space group R 3 with Z=3 for the R-centered setting. The magnetic moment per rhenium ion in Lu6ReO12 is 0.74(1)μB, and Yb6ReO12 orders antiferromagnetically below 2.15(10) K.

The two known phases of germanium nitride (Ge3N4) have hexagonal and trigonal symmetries and consist of three-dimensional networks of corner-connected Ge–N tetrahedra. A new cubic spinel phase (space-group Fd3m, a0=8.3 A, Z=8, ρ=6.36 g/cm3) containing Ge–N octahedra and tetrahedra in a 2:1 ratio was synthesized from elemental germanium and molecular nitrogen starting materials in a laser-heated diamond-anvil cell above 14 GPa. This phase is isostructural to the recently discovered cubic spinel phase of Si3N4.

The silica species contained in an aged clear suspension, which upon heating gives rise to the crystallization of Silicalite-1, were extracted with 80% efficiency using a sequence of acidification,...

Granular Ag–M alloys (M=Fe and Co) have been prepared by the gas-flow condensation technique, which involves co evaporation of the metals in continuous gas flow. The average grain size, determined from XRD data, increases from 7 to 16 nm for M=Fe and from 11 to 23 nm for M=Co, respectively, with increasing He-gas pressure. The XRD data have been confirmed by nitrogen adsorption measurements which revealed a decrease of the surface area with increasing pressure. The TEM analysis revealed the presence of isolated magnetic grains surrounded by Ag particles without alloying. Preliminary electrical measurements (at room temperature and in a magnetic field of 1.5 T) showed a decrease of the resistance variation with increasing He-gas pressure.

Ultra-fine, nanocrystalline zirconia/alumina (n-ZrO 2 /Al 2 O 3 ) powders are synthesized by chemical vapor synthesis (CVS) using a variable, modular gas flow reactor. Results for three different n-ZrO 2 /Al 2 O 3 powders are presented: single phase particles formed by doping zirconia with alumina, coated particles, and composite powder consisting of mixed particles of n-Al 2 O 3 and n-ZrO 2 .

Mn(ReO{sub 4}){sub 2}{center_dot}2H{sub 2}O (manganese(II)-perrhenate dihydrate) is analyzed by X-ray single-crystal diffraction and TG/DTA. Space group C2/m, a = 14.71(1) {angstrom}, b = 5.861(6) {angstrom}, c = 5.537(5) {angstrom}, {beta} = 110.87(4){degree}, Z = 2, calculated density D{sub x} = 4.40 g/cm{sup 3}. Chains of interconnected ReO{sub 4}-tetrahedra and MnO{sub 4}(OH{sub 2}){sub 2}-octahedra run parallel [0 1 0]. The AC-susceptibility ({mu}{sub eff} = 5.7 {mu}{sub B}) is consistent with divalent Mn and heptavalent Re. Dehydration takes place in a single step at 150 C. Decomposition starts at 820 C. The dehydration product Mn(ReO{sub 4}){sub 2} and the isotypic anhydrous perrhenates of Co, Ni, Zn crystallize in space group P{bar 3}, Z = 1; a ranges from 5.67 (Ni) to 5.86 {angstrom} (Mn), c ranges from 6.07 (Mn) to 6.17 {angstrom} (Zn), D{sub x} (g/cm{sup 3}) = 5.11 (Mn), 5.36 (Co), 5.44 (Ni), 5.33 (Zn). The structure is topologically equivalent to that of {beta}-Zr(MoO{sub 4}){sub 2}. M{sup 2+}O{sub 6}-octahedra are linked by ReO{sub 4}-tetrahedra to form layers which are not interconnected.

Three distinct phases of CuMoO 4 were observed and characterized by crystal structure analysis from single crystal and powder X-ray diffraction data. The phase stable at room temperature and ambient pressure is α -CuMoO 4 . A phase transition from α -CuMoO 4 to γ -CuMoO 4 is observed in single crystal experiments during cooling at 190 K for ambient pressure as well as for increasing pressure at 0.2 GPa and room temperature. At temperatures above 500 K and with pressure applied both α - and γ -CuMoO 4 transform to CuMoO 4 -III of distorted wolframite structure. If pressure is released after cooling, CuMoO 4 -III remains stable to the lowest temperatures examined, but an irreversible transition from CuMoO 4 -III to α -CuMoO 4 with a transition enthalpy of −15.3 kJ/mol occurs at T =752 K if heated without pressure applied. In this contribution the proposed p – T phase diagram of CuMoO 4 is determined with energy dispersive synchrotron radiation from powder sample from ambient pressure up to 7.0 GPa and in the temperature range between 180 and 1293 K. The high-pressure modifications of CuMoO 4 are also obtained under ambient conditions, if some of the Mo ions are replaced by W. A detailed discussion of the structural relationship between α - and γ -CuMoO 4 is given.

The existence of a continuous series of solid solutions NaCaCdMg 2 [(PO 4 ) 1− x (AsO 4 ) x ] 3 (0≤ x ≤1) suggests an alluaudite-like structure of the arsenate NaCaCdMg 2 (AsO 4 ) 3 . This is definitely confirmed by a Rietveld analysis of its X-ray powder diffractogram. The crystal cell is monoclinic, space group C 2/ c , with a =12.2363(1), b =12.9869(1), c =6.7742(1)A, β =113.7985(3)°. The Mg 2+ cations are essentially located on the M (2) sites of the alluaudite structure, but the distribution of the Na + , Ca 2+ , and Cd 2+ cations over the M (1), X (1), and X (2) sites is more or less disordered. The existence of a partial disorder in the cation distribution is supported by some diffuseness of the Raman and IR spectra.

YBa2Cu3O7 (YBCO) thin films with c-axis orientation on (001) SrTiO3, (001) MgO and (110) NdGaO3 substrates were examined by four-circle diffractometry with Co Kα and synchrotron radiation (λ = 0.1540 nm) using the q-scan technique. Small local film rotations about [001] have been introduced by two different mechanisms: (1) the orthorhombic/tetragonal phase transition driven by iron substitution or changes of the oxygen content; (2) heavy-ion irradiation (1.4 GeV 238U UNILAC, GSI Darmstadt). In the original orthorhombic state, the (110) axes of film and substrate are parallel so that the (100)film axes form an angle of 0.45° to those of the substrate. With decreasing orthorhombicity, this angle decreases to zero for tetragonal symmetry. Irradiation of the orthorhombic film by heavy ions produces detwinning and leads to a macroscopic preferential parallel alignment of the 〈100〉 axes of film and substrate. This reorientation is completed for a dose between 1011 and 1012 particles cm−2. High-resolution transmission electron microscopy investigations reveal a rotation of crystallites in the ab plane of irradiated samples of up to 3°. For irradiation with 200 (456) MeV 40Ca, no detwinning is observed.

NaNO3, R[unk]c, a = 5.0701(2) Å, c = 16.822(2) Å, V = 374.4 Å3, Z = 6. Neutron diffraction: λ = 0.87013 Å, μ = 0.1 cm−1, F(000) = 182.1 fm. The intensities are checked for normal and independent distribution and their Poisson variances are modified with the aid of χ 2 values of repeatedly measured intensities. Refinement on |F|2 including weak and negative intensities. Anharmonic motion of N and O up the third order of a Gram-Charlier expansion was refined. R = 0.032, wR = 0.026, S 2 = 1.99, 3642 measured and 317 unique intensities, 17 parameters. Synchrotron X-ray diffraction: λ = 0.56 Å, F(000) = 78e, refinement on |F|. Anharmonic motion of N and O up to the fourth order of a Gram-Charlier expansion was refined. R = 0.020, wR = 0.007, S 2 = 1.51,443 unique intensities, 39 parameters. No ±180° Ising-type in plane orientational disorder of NO3-groups is observed at 293 K. Multipolar expansion of the electron density reveals bonding electrons and a strong deformation of the atoms within the planar NO3-group.

Nanocgstalline Pd and ZrO2 samples of theoretical density were irradiated with 4 MeV Kr+ions with doses up to 6.1017 ion/cm2. The irradiated samples were characterized by XRD, RBS, and TEM. Nanocrystalline ZrO2 shows no amorphisation and defect agglomeration after irradiation with Kr+ ions up to a dose of 2·1017 ions/cm2. A phase transformation from the monoclinic phase to a tetragonal phase could be observed. The comparison of irradiated n-Pd with a conventional polycrystalline Pd sample shows a reduced defect agglomeration in n-Pd. For n-Pd samples grain growth after irradiation experiments could be observed.