• Structure and properties of complex hydride perovskite materials
    P. Schouwink, M.B. Ley, A. Tissot, H. Hagemann, T.R. Jensen, L. Smrcok and R. Cern
    Nature Communications, 5 (2014), p5706
    DOI:10.1038/ncomms6706 | unige:43536 | Abstract | Article HTML
Perovskite materials host an incredible variety of functionalities. Although the lightest element, hydrogen, is rarely encountered in oxide perovskite lattices, it was recently observed as the hydride anion H, substituting for the oxide anion in ​BaTiO3. Here we present a series of 30 new complex hydride perovskite-type materials, based on the non-spherical ​tetrahydroborate anion ​BH4 and new synthesis protocols involving rare-earth elements. Photophysical, electronic and ​hydrogen storage properties are discussed, along with counterintuitive trends in structural behaviour. The electronic structure is investigated theoretically with density functional theory solid-state calculations. BH4-specific anion dynamics are introduced to perovskites, mediating mechanisms that freeze lattice instabilities and generate supercells of up to 16 × the unit cell volume in AB(BH4)3. In this view, homopolar hydridic di-hydrogen contacts arise as a potential tool with which to tailor crystal symmetries, thus merging concepts of molecular chemistry with ceramic-like host lattices. Furthermore, anion mixing ​BH4−←X (X=Cl−, Br, I) provides a link to the known ABX3 halides.
  • Bimetallic Borohydrides in the System M(BH4)2–KBH4 (M = Mg, Mn): On the Structural Diversity
    P. Schouwink, V. D'Anna, M.B. Ley, L.M. Lawson Daku, B. Richter, T.R. Jensen, H. Hagemann and R. Cern
    The Journal of Physical Chemistry C, 116 (20) (2012), p10829-10840
    DOI:10.1021/jp212318s | unige:21580 | Abstract | Article HTML | Article PDF
Four novel bimetallic borohydrides have been discovered, K2M(BH4)4 (M = Mg or Mn), K3Mg(BH4)5, and KMn(BH4)3, and are carefully investigated structurally as well as regarding their decomposition reaction mechanism by means of in situ synchrotron radiation powder X-ray diffraction (SR-PXD), vibrational spectroscopies (Raman and IR), thermal analysis (TGA and DTA), and ab initio density functional theory (DFT) calculations. Mechano-chemical synthesis (ball-milling) using the reactants KBH4, α-Mg(BH4)2, and α-Mn(BH4)2 ensures chlorine-free reaction products. A detailed structural analysis reveals significant similarities as well as surprising differences among the two isomorphs K2M(BH4)4, most importantly concerning the extent to which the complex anion [M(BH4)4]2– is isolated in the structure. Anisotropic thermal expansion and an increase in symmetry at high temperatures in K3Mg(BH4)5 is ascribed to the motion of BH4 groups inducing hydrogen repulsive effects, and the dynamics of K3Mg(BH4)5 are investigated. Decomposition in the manganese system proceeds via the formation of KMn(BH4)3, the first perovkite type borohydride reported to date.



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