title: Structural insights into M2O-Al2O3-WO3 (M = Na, K) system by electron diffraction tomography.
abstract: The M2O-Al2O3-WO3 (M = alkaline metals) system has attracted the attention of the scientific community because some of its members showed potential applications as single crystalline media for tunable solid-state lasers. These materials behave as promising laser host materials due to their high and continuous transparency in the wide range of the near-IR region. A systematic investigation of these phases is nonetheless hampered because it is impossible to produce large crystals and only in a few cases a pure synthetic product can be achieved. Despite substantial advances in X-ray powder diffraction methods, structure investigation on nanoscale is still challenging, especially when the sample is polycrystalline and the structures are affected by pseudo-symmetry. Electron diffraction has the advantage of collecting data from single nanoscopic crystals, but it is frequently limited by incompleteness and dynamical effects. Automated diffraction tomography (ADT) recently emerged as an alternative approach able to collect more complete three-dimensional electron diffraction data and at the same time to significantly reduce dynamical scattering. ADT data have been shown to be suitable for ab initio structure solution of phases with large cell parameters, and for detecting pseudo-symmetry that was undetected in X-ray powder data. In this work we present the structure investigation of two hitherto undetermined compounds, K5Al(W3O11)2 and NaAl(WO4)2, by a combination of electron diffraction tomography and precession electron diffraction. We also stress how electron diffraction tomography can be used to obtain direct information about symmetry and pseudo-symmetry for nanocrystalline phases, even when available only in polyphasic mixtures.
authors.affiliation: Institute of Physical Chemistry, Johannes Gutenberg University, Jacob Welderweg 11, 55128 Mainz, Germany.
authors.forename: Iryna
authors.initials: I
authors.lastname: Andrusenko
authors.affiliation: Institute of Physical Chemistry, Johannes Gutenberg University, Jacob Welderweg 11, 55128 Mainz, Germany.
authors.forename: Yaşar
authors.initials: Y
authors.lastname: Krysiak
authors.affiliation: Institute of Physical Chemistry, Johannes Gutenberg University, Jacob Welderweg 11, 55128 Mainz, Germany.
authors.forename: Enrico
authors.initials: E
authors.lastname: Mugnaioli
authors.affiliation: Institute of Physical Chemistry, Johannes Gutenberg University, Jacob Welderweg 11, 55128 Mainz, Germany.
authors.forename: Tatiana E
authors.initials: TE
authors.lastname: Gorelik
authors.affiliation: Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. 107, 1113 Sofia, Bulgaria.
authors.forename: Diana
authors.initials: D
authors.lastname: Nihtianova
authors.affiliation: Institute of Physical Chemistry, Johannes Gutenberg University, Jacob Welderweg 11, 55128 Mainz, Germany.
authors.forename: Ute
authors.initials: U
authors.lastname: Kolb
keywords: electron crystallography; electron difffraction tomography; laser media; structure determination; tungstate