Synthese und Charakterisierung von neuen Sodalithen, Cancrinithen sowie deren Intermediären Phase

The thermal behavior and occuring phase transitions of three sodalites, a permanganate-, a perrhenate and a mixed permanganate/perrhenate-sodalite are investigated. Below 300 K a loss of dynamic motion of the templating anions could be observed, causing a phase transition of perrhenate-sodalite. At elevated temperatures all sodalites show a phase transition to the fully expanded structure (P-43n to Pm-3n). At 900 K the permangante-sodalite shows a second phase transition to P23.Further a comprehensive study on cancrinites containing different divalent tetrahedral coordinated anions (XO4 2-; X = Mn, Cr, Se, Mo, W) and their effect on the thermal behavior is performed. Thirdly, a structural investigation of the one-dimensional disordered Intermediate phase is carried out. By correlating the lattice parameter c with the existing zeolite-cages and the chemical composition of the sample the structure of the intermediate phase could be modeled

Synthesis and characterization of new sodalites, cancrinites and their intermediate phase

The thermal behavior and occuring phase transitions of three sodalites, a permanganate-, a perrhenate and a mixed permanganate/perrhenate-sodalite are investigated. Below 300 K a loss of dynamic motion of the templating anions could be observed, causing a phase transition of perrhenate-sodalite. At elevated temperatures all sodalites show a phase transition to the fully expanded structure (P-43n to Pm-3n). At 900 K the permangante-sodalite shows a second phase transition to P23.Further a comprehensive study on cancrinites containing different divalent tetrahedral coordinated anions (XO4 2-; X = Mn, Cr, Se, Mo, W) and their effect on the thermal behavior is performed. Thirdly, a structural investigation of the one-dimensional disordered Intermediate phase is carried out. By correlating the lattice parameter c with the existing zeolite-cages and the chemical composition of the sample the structure of the intermediate phase could be modeled

Disordered but primitive gallosilicate hydro-sodalite: Structure and thermal behaviour of a framework with novel cation distribution

The structure of a new gallosilicate sodalite |Na6.16(1)(H2O)8|[Ga1.04(1)Si0.96(1)O4]6 described in space group with lattice parameter a = 885.208(7) pm is reported. For such a sodalite with a deviation from a 1:1 ratio in the framework cations a body-centred structure in space group could be expected. The structure shows structural stress resulting from this unusual substitution by a high strain visible in reflections which are forbidden by symmetry in . Distinct amounts of Ga and Si are redistributed on the opposite crystallographic position. The second coordination sphere of Si was examined by 29Si MAS NMR, the absence of OH− in the sodalites cages was checked by FTIR- and Raman spectroscopy. The intensity distribution of MAS NMR signal is modelled using a new technique to calculate the framework metal second neighbour coordination. The confirmed distribution leads to a low thermal stability of the cubic sodalite indicated by a new intermediated phase which could be regarded as a triclinic distorted cancrinite with three-time increased c lattice parameter. This intermediate phase decomposes at around 1000 K to a beryllonite-type sodium gallosilicate.20621

In situ synchrotron x-ray diffraction studies monitoring mechanochemical reactions of hard materials: Challenges and limitations

In situ monitoring of mechanochemical reactions of soft matter is feasible by synchrotron diffraction experiments. However, so far, reactions of hard materials in existing polymer milling vessels failed due to insufficient energy input. In this study, we present the development of a suitable setup for in situ diffraction experiments at a synchrotron facility. The mechanochemical transformation of boehmite, $γ$-AlOOH, to corundum, $\alpha$-Al$_2$O$_3$, was chosen as a model system. The modifications of the mill’s clamping system and the vessels themselves were investigated separately. Starting from a commercially available Retsch MM 400 shaker mill, the influence of the geometrical adaptation of the setup on the milling process was investigated. Simply extending the specimen holder proved to be not sufficient because changes in mechanical forces need to be accounted for in the construction of optimized extensions. Milling vessels that are suitable for diffraction experiments and also guarantee the required energy input as well as mechanical stability were developed. The vessels consist of a steel body and modular polymer/steel rings as x-ray transparent windows. In addition, the vessels are equipped with a gas inlet and outlet system that is connectable to a gas analytics setup. Based on the respective modifications, the transformation of boehmite to corundum could be observed in an optimized setup

Crystal Structures of Two Titanium Phosphate-Based Proton Conductors: Ab Initio Structure Solution and Materials Properties

Transition-metal phosphates show a wide range of chemical compositions, variations of the valence states, and crystal structures. They are commercially used as solid-state catalysts, cathode materials in rechargeable batteries, or potential candidates for proton-exchange membranes in fuel cells. Here, we report on the successful ab initio structure determination of two novel titanium pyrophosphates, Ti(III)p and Ti(IV)p, from powder X-ray diffraction (PXRD) data. The low-symmetry space groups P2$_1$/c for Ti(III)p and P$\overline{1}$ for Ti(IV)p required the combination of spectroscopic and diffraction techniques for structure determination. In Ti(III)p, trivalent titanium ions occupy the center of TiO$_6$ polyhedra, coordinated by five pyrophosphate groups, one of them as a bidentate ligand. This secondary coordination causes the formation of one-dimensional six-membered ring channels with a diameter d$_{max}$ of 3.93(2) Å, which is stabilized by NH$_{4}$$^{+}$ ions. Annealing Ti(III)p in inert atmospheres results in the formation of a new compound, denoted as Ti(IV)p. The structure of this compound shows a similar three-dimensional framework consisting of [PO$_4$]3– tetrahedra and Ti$^{IV+}$O$_6$ octahedra and an empty one-dimensional channel with a diameter d$_{max}$ of 5.07(1) Å. The in situ PXRD of the transformation of Ti(III)p to Ti(IV)p reveals a two-step mechanism, i.e., the decomposition of NH$_{4}$$^{+}$ ions in a first step and subsequent structure relaxation. The specific proton conductivity and activation energy of the proton migration of Ti(III)p, governed by the Grotthus mechanism, belong to the highest and lowest, respectively, ever reported for this class of materials, which reveals its potential application in electrochemical devices like fuel cells and water electrolyzers in the intermediate temperature range