Sven-Ulf Weber's research while affiliated with Technische Universität Braunschweig and other places

... Central quantity in this respect is the electric field gradient (EFG) whose main property consists in providing the link between crystallography and solid-state physics or between diffractometry and spectroscopy, respectively. Recently, this has been proved at a special example [1]. ...

... These Dy 3+ are coordinated by eight oxygen atoms forming distorted DyO 8 polyhedra linked to each other, building a 4-ring channel ( Figure 1). The infinite octahedral chains are the dominant (but not only 3 ) criterion for mullite-type phases which could be subdivided into so-called O8-phase [11][12][13][14] (e.g., PbMBO 4 11-13,15-17 and schafarzikites LM 2 O 4 [18][19][20][21][22][23][24][25] ), O9-phase (e.g., BiMO [26][27][28][29][30][31][32][33][34][35][36][37][38] and ABO [39][40][41][42][43][44], and O10-phase (e.g., BiMO 6,10,45,46 ). The DyMn 2 O 5 structure type belongs to the O10 phase which differs from the O9 BiMO phases with only an additional oxygen atom. ...

... Semiconducting materials showing photocatalytic activity by forming excitons in the visible electromagnetic spectrum are highly demanded nowadays [1][2][3][4][5]. In this regard mullite [6][7][8] and mullite-type materials of either O8 EMBO 4 [9][10][11][12][13][14] and Schafarzikite [15][16][17][18], O9 [19][20][21] or O10 [22][23][24] type, especially the multiferroic O9 phase Bi 2 Fe 4 O 9 [25][26][27][28], are widely used [29][30][31][32][33][34][35][36][37][38]. The respective pseudo-binary phase diagram Bi 2 O 3 -Fe 2 O 3 has been repeatedly investigated [39][40][41][42][43][44][45], providing descriptions of some thermodynamically stable phases such as perovskitetype BiFeO 3 [32,43], mullite-type Bi 2 Fe 4 O 9 [25,28,29,31,32,[34][35][36][37][38][46][47][48] and sillenite-type Bi 25 FeO 40 [40]. ...

... In the course of our systematic investigation of minerals with low iron content, it has been demonstrated that the electric field gradient (EFG) tensor is the most valuable quantity as supplying information on local distortions not amenable to conventional diffraction methods (Weber et al. 2009 and references therein). Moreover, it is a key quantity in studying the relationship between structural and chemical properties in solids because it provides a sensitive measure for the size and symmetry of the electric charge distribution around a given nucleus at a certain crystallographic site. ...

... Beryllium occupies tetrahedra and Al occupies two types of slightly distorted interstitial octahedral sites: B1 octahedra with Ci symmetry and B2 octahedra with Cs symmetry [9]. These octahedra have different volumes; additionally, B2 has an Al-O distance of 1.936 Å, which is larger than B1, with an Al-O distance of 1.890 Å [10]. Alexandrite is a type of chromium-doped bearing chrysoberyl in which Cr 3+ is substituted in the Al 3+ sites. ...

... We suspect that elevated paramagnetic iron concentration (our mineral is brown in color, which is likely caused by an O 2− → Fe 3+ charge transfer and Fe 2+ in octahedral coordination in sinhalite) led to increased 25 Mg nuclear spin relaxation rates and a distribution of Fermi contact shifts, inhibiting 25 Mg NMR spectral acquisition. 64 Grandidierite, MgAl 3 (BO 4 )(SiO 4 )O, crystallizes in orthorhombic space group Pbnm and features one crystallographically unique Mg atom in an [MgO 5 ] polyhedron. 60 Grandidierite has been studied previously by MacKenzie and Meinhold 7 and was one of the first crystalline compounds with a pentacoordinated Mg site to be investigated by 25 Mg MAS NMR spectroscopy. ...

... The extremely high sensitivity of Mössbauer spectroscopy and its ability to distinguish Fe 2+ from Fe 3+ is of great advantage in assessing the oxidation state of iron. Another advantage is also the ability of the method to analyze microcrystalline and amorphous substances containing iron [11][12][13]. It was shown that during the synthesis of CNTs a change occurred in the oxidation degree and in the binding of the iron atoms in the catalyst [14,15]. ...