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Hygroscopic single crystals of a new hexagonal high‐temperature modification of Sr[ReO4]2 were prepared from a melt of Sr[ReO4]2 ⋅ H2O and SrCl2 ⋅ 6 H2O. The structure analysis of the obtained crystals by X‐ray diffraction revealed that the title compound crystallizes in the ThCd[MoO4]3‐type structure with the hexagonal space group P63/m and the lattice parameters a=1023.81(7) pm and c=646.92(4) pm (c/a=0.632) for Z=2 in its quenchable high‐temperature form. Two crystallographically independent Sr2+ cations are coordinated by oxygen atoms forming either octahedra or tricapped trigonal prisms, whereas the Re7+ cations are found in the centers of discrete tetrahedral meta‐perrhenate units [ReO4]−. Temperature‐dependent in‐situ PXRD studies of dry powder samples of Sr[ReO4]2 exhibited its thermal dimorphy with a phase‐transition temperature at 500–550 °C from literature‐known m‐Sr[ReO4]2 into the newly discovered h‐Sr[ReO4]2 (hexagonal). [ABSTRACT FROM AUTHOR]

Hygroscopic single crystals of a new hexagonal high‐temperature modification of Sr[ReO4]2 were prepared from a melt of Sr[ReO4]2 ⋅ H2O and SrCl2 ⋅ 6 H2O. The structure analysis of the obtained crystals by X‐ray diffraction revealed that the title compound crystallizes in the ThCd[MoO4]3‐type structure with the hexagonal space group P63/m and the lattice parameters a=1023.81(7) pm and c=646.92(4) pm (c/a=0.632) for Z=2 in its quenchable high‐temperature form. Two crystallographically independent Sr2+ cations are coordinated by oxygen atoms forming either octahedra or tricapped trigonal prisms, whereas the Re7+ cations are found in the centers of discrete tetrahedral meta‐perrhenate units [ReO4]−. Temperature‐dependent in‐situ PXRD studies of dry powder samples of Sr[ReO4]2 exhibited its thermal dimorphy with a phase‐transition temperature at 500–550 °C from literature‐known m‐Sr[ReO4]2 into the newly discovered h‐Sr[ReO4]2 (hexagonal). [ABSTRACT FROM AUTHOR]

The title compound, Zn4Cu3(Zn1–xCux)6(HCOO)8(OH)18·6(H2O), also denoted as "Zinc C", a previously unknown corrosion phase of brass in contact with glass, was found on four different historic objects stored in three different collections. Model experiments demonstrated that formaldehyde emitted e.g. from wooden cabinets undergoes a Cannizarro reaction in the alkaline surface film on the historic glass making formate available for the formation of this corrosion phase. The crystal structure of "Zinc C" was solved ab initio from X‐ray powder diffraction data. From the crystal structure and EDX analyses, a phase composition of Zn4Cu3(Zn1–xCux)6(HCOO)8(OH)18·6(H2O) was derived. Zinc C crystallizes in a trigonal unit cell in space group R3(148) with lattice parameters of a = 10.9185(1) Å, c = 27.5058(4) Å, and V = 2839.74(6) Å3. Layers of edge sharing MO6/3 octahedra with voids capped by Zn(HCOO) forming Zn(HCOO)(OH)3/3 tetrahedra are the main motif in the structure. The zinc/copper ratio of the corrosion phase "Zinc C" can vary between 10:3 and 4:9, due to a partial occupational disorder between copper and zinc in the crystal structure. A corrosion phase found on historic brass objects was characterized and identified as Zn4Cu3(Zn1–xCux)6(HCOO)8(OH)18·6(H2O). The crystal structure exhibits a layered motif with a partial occupational disorder between copper and zinc. Model experiments demonstrate that the corrosion was induced by partial hydrolysis of the historic glass. [ABSTRACT FROM AUTHOR]

Although carbonyl iron powder (CIP) is an old material for magnetic applications (e.g. inductor cores), the structure of this material is still described controversially in literature. On the first glance a greyish powder exhibiting a spherical structure, CIP reveals on the second glance a nanoscopic crystalline sub-structure. The material itself contains carbon and nitrogen and its structure is described as an onion-type structure. However, the nature of the different shells and clarity on the nature of the involved carbidic and/or nitridic phases, be they crystalline, amorphous or solid solutions has not yet been achieved. In addition, it is known, that CIP transforms in H2-atmosphere to a "soft" grade, consisting of pure Fe. Again, chemical and microstructural knowledge on the transition from the "hard" to the "soft" CIP is lacking. This leads to the motivation of this study: 1. Unambiguously identify the nature and existence of the involved phases in the unreduced and hard carbonyl iron powder and in the reduced and soft iron powder particles 2. Characterize the phase transformations and microstructural changes of CIP during the thermic treatment in a hydrogen atmosphere. Different techniques were used to clarify the above mentioned points like in-situ synchrotron XRPD accompanied by electron microscopy techniques. [ABSTRACT FROM AUTHOR]

The solid/liquid equilibria in the ternary system Ni(OH)2-NiCl2-H2O at temperatures of 25 and 200 °C have been investigated by applying equilibration periods of up to 45 months (3 years and 9 months). The equilibration process was studied by isothermal saturation methods using different solids as starting materials. At 200 °C, Ni2Cl(OH)3 and NiCl(OH) occur as stable phases, whereas a solid solution, NiClx(OH)2-x (ss-type-OH), appears as an intermediate phase. At 25 °C, two nickel(II) chloride hydroxide hydrates, Ni3Cl2+x(OH)4-x·4H2O and Ni3Cl(OH)5·4H2O, are formed. The latter phase was characterized for the first time and a structural model was created from a Rietveld refinement of the powder X-ray diffraction pattern. A systematic investigation of the solubilities at 25 °C revealed that Ni2Cl(OH)3 is the solid phase in both dilute and concentrated NiCl2 solutions at this temperature. In general, all stable and metastable phases in the system Ni(OH)2-NiCl2-H2O exhibit very low solubility, but during the very slow phase transformations high hydroxide supersaturations occur that are persistent for years. [ABSTRACT FROM AUTHOR]

Phase-pure ScF[SeO3] and YF[SeO3] were synthesized via solid-state reactions of the corresponding rare-earth metal sesquioxides and trifluorides with selenium dioxide in excess of fluxing cesium bromide at 700 °C for 7 d. To avoid the formation of oxosilicates, these reactions took place in corundum crucibles embedded inside of evacuated fused silica ampoules. Upon cooling down below 13 °C, a pseudo-second-order phase transition ( P21/ m → P $\bar{1}$ or P1) for ScF[SeO3] occurs, which is similar to the high-temperature phase transition of LuF[SeO3]. By heating YF[SeO3] above 319 °C, it undergoes a first-order phase transition ( P21/ c → P21/ m) without passing the intermediate P $\bar{1}$ modification in contrast to LuF[SeO3]. Both the high-temperature phase transition of YF[SeO3] and the low-temperature phase transition of ScF[SeO3] were characterized by in-situ X-ray powder diffraction, X-ray single-crystal diffraction, thermal analysis DSC, and distortion-mode analysis. For both cases the driving forces for the symmetry-breaking phase transitions from the high- to the low-temperature phases are discussed. [ABSTRACT FROM AUTHOR]

Phase transitions recorded using in-situ powder diffraction are typically analysed by Rietveld refinements applying relative atomic coordinates in a least-squares iteration process. Although this choice of relative atomic coordinates gives an intuitive coordinate system, it can be improved by changing to another basis of the atomic configuration space, as the motion of whole atomic groups or polyhedra can be normally described with a smaller set of parameters. Using rotational rigid body symmetry modes as another basis, it is possible to directly describe and refine the rotation of groups of atoms (denoted as constrainable atomic groups). In addition, a reduction of the total number of relevant parameters can occur. In order to explore the capabilities of this new approach, phase transitions in different compounds, namely sodium niobate (NaNbO3), ferrocene (Fe(C5H5)2), and schafarzikite (FeSb2O4) are reinvestigated. [ABSTRACT FROM AUTHOR]

In the course of solid-state photoreactions, a single crystal (SC) of the reactant can be transformed into an SC of the product or it can lose crystallinity and become amorphous. In-between these two scenarios exist the reconstructive phase transformations, where upon irradiation, the reactant SC becomes a powder or an SC with increased mosaicity. We present a detailed description of reconstructive photodimerization, where the structural changes are directly correlated with the disintegration process. The kinetics of the reaction is explained by two kinetic regimes, forming an autocatalytic autoinhibition photoreaction set with high quantum yield. In addition, the photoreaction pathways were studied theoretically. [ABSTRACT FROM AUTHOR]

Sequential Rietveld refinements were applied on high-pressure synchrotron powder X-ray diffraction measurements of lanthanum ferrite (LaFeO3) revealing two phase transitions on the room-temperature isotherm up to a pressure of 48 GPa. The first structural phase transition of second order occurs at a pressure of 21.1 GPa, changing the space group from Pbnm to Ibmm. The second transition, involving a isostructural first-order phase transition, occurs at approximately 38 GPa, indicating a high-spin to low-spin transition of the Fe3+ ion. Following the behavior of the volume up to the hydrostatic limit of methanol-ethanol it was possible to use inverted equations of state (EoS) to determine a bulk modulus of B0 = 172 GPa and a corresponding pressure derivative of B′0 = 4.3. In addition, the linearized version of the inverted EoS were used to determine the corresponding moduli and pressure derivatives for each lattice direction. [ABSTRACT FROM AUTHOR]

The high-temperature phase transition of LuF[SeO3] has been characterized by time-resolved high-resolution synchrotron powder diffraction. On heating, a second-order structural phase transition was found at 393 K, while on cooling the same phase transition occurs at 371 K, showing a large hysteresis typical for a first-order phase transition. Detailed analysis using sequential and parametric whole powder pattern fitting revealed that the coupling between the strain and the displacive order parameter determines the behaviour of the material during the phase transition. Different possible coupling mechanisms have been evaluated and the most probable rationalized. [ABSTRACT FROM AUTHOR]

Abstract: The solid-state phase transformation of different polymorphic forms of copper phthalocyanine to the thermodynamically most stable β-modification was investigated so as to evaluate the influence of mixtures of different polymorphs and additives upon the order of the reaction from isothermal X-ray powder diffraction data. The data were analysed by sequential Rietveld refinement and the results evaluated using both Avrami and Arrhenius equations. The order of the reaction was significantly influenced by the availability of initially present β-copper phthalocyanine and both the nucleation rate and dimensionality of crystal growth depended strongly on sample composition and reaction temperature. [Copyright &y& Elsevier]

Abstract: The thermal behavior of AgNCO (silver isocyanate) has been studied via thermal analysis, optical spectroscopy, X-ray powder diffraction and transmission electron microscopy. Upon quenching the high temperature polymorph (HT-AgNCO) to room temperature, a new modification has been obtained (q-AgNCO). Its crystal structure was solved from X-ray powder diffraction data and refined by the Rietveld method (Pmmn (no. 59), a =3.579(3)Å, b =5.777(4)Å, c =5.807(2)Å, V =120.08(3)Å3, Z =2, T =295K). The structure consists of chains of Ag+ ions bridged by isocyanate units. HT-AgNCO exists between T =135°C and the melting/decomposition point and exhibits virtually free rotation of the complex anions. According to preliminary single-crystal studies, HT-AgNCO (C2/m, a =5.87Å, b =3.51Å, c =5.81Å, ß =105.953°, Z=2, T =373K) is structurally related to α-NaN3. The crystal structures of both, HT-AgNCO and q-AgNCO have been compared with that of the room temperature modification (RT-AgNCO). The thermal behavior and the ionic conductivity of AgNCO are discussed with respect to the related compounds AgN3 and KSCN. Decomposition of AgNCO proceeds in distinct steps, as seen from TGA, and results in the formation of nanoparticles of elemental silver and an amorphous polymer consisting of C, N and O, only. [Copyright &y& Elsevier]

The compounds tetrakis(trimethylstannyl )germane, Ge(SnMe3)4 (1), and tetrakis(trimethylstannyl)silane, Si(SnMe3)4 (2), have crystal structures with the quasispherical rnolecules in a closed-packed stacking. At room temperature both structures have the space group P&macr1; (Z = 2) with a = 9.94457 (5), b = 14.52927 (8). c = 916021 (5) Å, α = 90.53390 (30), β = 11.L73080 (30), γ = 90.0049 (4)°, and V = 1229.414 (12) ų for (1) and a = 9.92009 (7), b = 14.51029 (11), c = 9.13585 (7) Å, α = 90.4769 (4), β = 111.6724 (4), γ = 89..9877 (6)°, and V = 1222.037 (16) ų for (2). The molecules are found to be ordered as a result of steric interactions between neighboring molecules, as shown by analyzing the distances between the atoms. Upon heating, both compounds undergo a first-order phase transition at temperatures Tc = 348 ± 5 K, as characterized by a relative jump of the lattice parameter of ∼16%. At 353 K, both structures have the space group P&macr1;(Z = 4). with a = 14.2037 (2) Å, and V = 2865.52 (7) &ARing;³ for (1) and a = 14.1346 (2) &ARing;, and V = 2823.90 (7) ų for (2). Rietveld refinements were performed for the low-temperature phases measured at T = 295 K [Rwp = 0.0844 for (1). Rwp = 0.0940 for (2)] and for the high- temperature phases measured at T = 353 K [Rwp = 0.0891 for (I), Rwp = 0.0542 for (2)]. The combination of high-resolution X-ray powder diffraction measurements and variable-temperature magic-angle-spinning 13C, 29Si and 119Sn NMR experiments demonstrates low crystallographic and molecular (C1) symmetries for the low-temperature phases of (1) and (2) at temperatures T < 348 ± 5 K and high crystaftiographic symmetry due to rotational disorder for the high-temperature phases at temperatures T < 348 ± 5 K. [ABSTRACT FROM AUTHOR]

The pressure dependence of the crystal structure of cubic tetrakis(trirnethylsilvl)methane C[Si(CH3)3]4 (TC) (P < 16.0 GPa, T = 298 K) is reported using high-resolution angle-dispersive X-ray powder diffraction. The compound has crystal structures with the molecules in a cubic-close- packed (c.c.p.) arrangement. It shows three phase transitions in the measured pressure range. At ambient conditions, TC has space group Pm&macr3;m (Z = 4) with a = 12.8902 (2) Å. V = 2141.8 (1) ų (phase I). Between 0 and 0.13 GPa TC exhibits a first-order phase transition into a structure with space group Pa&macr3; (phase II).. A second first-order phase transition occurs between 0.2 and 028 GPa into a structure with space group P213 (phase III). Under non-hydrostatic pressure conditions (P > 10 GPa) a transformation is observed into a c.c.p. structure that is different from the face-centred-cubic structure at ambient conditions. A non-linear compression behaviour is observed, which could be described by a Vinet relation in the range 0.28-4.8 GPa. The extrapolated bulk modulus of the high-pressure phase III was determined to be K0 = 7.1 (8) GPa. The crystal structures in phase III are refined against X-ray powder data measured at several pressures between 0.49 and 4.8 GPa, and the molecules are found to be fully ordered. This is interpreted to result from steric interactions between neighbouring molecules, as shown by analysing the pressure dependence of intramolecular angles, torsion angles and intermolecular distances. Except for their cell dimensions, phases I. II and III are found to be isostructural to the corresponding phases at low temperatures. [ABSTRACT FROM AUTHOR]

LuF[SeO3] is a compound that can easily be obtained by a solid-state reaction of Lu2O3, LuF3, and SeO2 with CsBr as the fluxing agent. The outstanding property of LuF[SeO3] is the appearance of two phase transitions within a range of less than 200 K. With an increase in the coordination number for Lu3+ from 7 to 8, the tridinic room-temperature modification changes at temperatures below --40 °C to the monoclinic low-temperature or high-pressure phase of LuF-[SeO3]. At the same time, room-temperature modification retains the structure but gains higher symmetry at the second phase transition of around +110 °C. This second transition can even be observed under a microscope using polarized light to see twinning lamellae disappear and reappear during this reversible process. [ABSTRACT FROM AUTHOR]

The Front Cover shows historic glass earrings with brass mountings from the Hamburg Museum in the background. The metal parts exhibit severe corrosion, especially where they are in contact with glass. The partial dissolution of the historic glass by moisture leads to a surface film containing formates produced by a Canizzaro reaction of formaldehyde, emitted by, e.g., wooden furniture, with the alkaline components of the film. An excerpt of the crystal structure of a new corrosion phase, Zn4Cu3(Zn1–xCux)6(HCOO)8(OH)18·6(H2O) ("Zinc C"), is presented. More information can be found in the Full Paper by S. Bette et al. For more on the story behind the cover research, see the Cover Profile. [ABSTRACT FROM AUTHOR]

The high-temperature phase transition of LuF[SeO3] has been characterized by time-resolved high-resolution synchrotron powder diffraction. On heating, a second-order structural phase transition was found at 393 K, while on cooling the same phase transition occurs at 371 K, showing a large hysteresis typical for a first-order phase transition. Detailed analysis using sequential and parametric whole powder pattern fitting revealed that the coupling between the strain and the displacive order parameter determines the behaviour of the material during the phase transition. Different possible coupling mechanisms have been evaluated and the most probable rationalized. [ABSTRACT FROM AUTHOR]

Phase-pure ScF[SeO3] and YF[SeO3] were synthesized via solid-state reactions of the corresponding rare-earth metal sesquioxides and trifluorides with selenium dioxide in excess of fluxing cesium bromide at 700 °C for 7 d. To avoid the formation of oxosilicates, these reactions took place in corundum crucibles embedded inside of evacuated fused silica ampoules. Upon cooling down below 13 °C, a pseudo-second-order phase transition ( P21/ m → P $\bar{1}$ or P1) for ScF[SeO3] occurs, which is similar to the high-temperature phase transition of LuF[SeO3]. By heating YF[SeO3] above 319 °C, it undergoes a first-order phase transition ( P21/ c → P21/ m) without passing the intermediate P $\bar{1}$ modification in contrast to LuF[SeO3]. Both the high-temperature phase transition of YF[SeO3] and the low-temperature phase transition of ScF[SeO3] were characterized by in-situ X-ray powder diffraction, X-ray single-crystal diffraction, thermal analysis DSC, and distortion-mode analysis. For both cases the driving forces for the symmetry-breaking phase transitions from the high- to the low-temperature phases are discussed. [ABSTRACT FROM AUTHOR]

Sequential Rietveld refinements were applied on high-pressure synchrotron powder X-ray diffraction measurements of lanthanum ferrite (LaFeO3) revealing two phase transitions on the room-temperature isotherm up to a pressure of 48 GPa. The first structural phase transition of second order occurs at a pressure of 21.1 GPa, changing the space group from Pbnm to Ibmm. The second transition, involving a isostructural first-order phase transition, occurs at approximately 38 GPa, indicating a high-spin to low-spin transition of the Fe3+ ion. Following the behavior of the volume up to the hydrostatic limit of methanol-ethanol it was possible to use inverted equations of state (EoS) to determine a bulk modulus of B0 = 172 GPa and a corresponding pressure derivative of B′0 = 4.3. In addition, the linearized version of the inverted EoS were used to determine the corresponding moduli and pressure derivatives for each lattice direction. [ABSTRACT FROM AUTHOR]