@Article{JPhysCondensMatter_27_265403, author = {P. Schouwink and H. Hagemann and J.P. Embs and V. D'Anna and R. Cerný}, title = {{Di-hydrogen contact induced lattice instabilities and structural dynamics in complex hydride perovskites}}, journal= {J. Phys.: Condens. Matter}, ISSN = {0953-8984}, volume= {27}, number= {26}, pages = {265403}, url = {http://iopscience.iop.org/0953-8984/27/26/265403/}, eprint= {http://www.unige.ch/sciences/chifi/publis/refs_pdf/ref01477.pdf}, doi= {10.1088/0953-8984/27/26/265403}, keywords= {perovskite;hydride;quasielastic neutron scattering;phase transition}, abstract = {{The structural phase transitions occurring in a series of perovskite-type complex hydrides based on the tetrahydroborate anion BH$_4^-$ are investigated by means of {\em in situ} synchrotron x-ray powder diffraction, vibrational spectroscopy, thermal methods and {\em ab initio} calculations in the solid state. Structural dynamics of the BH4 anion are followed with quasi-elastic neutron scattering. We show that unexpected temperature-induced lattice instabilities in perovskite-type {\em A}Ca(BH$_4$)$_3$ ({\em A} = K, Rb, Cs) have their origin in close hydridic di-hydrogen contacts. The rich lattice dynamics lead to coupling between internal B-H vibrations and phonons, resulting in distortions in the high-temperature polymorph that are identical in symmetry to well-known instabilities in oxide perovskites, generally condensing at lower temperatures. It is found that anion-substitution BH$_4^-$ ↔ X$^-$ (X = Halide) can relax distortions in {\em A}Ca(BH4)3 by eliminating coulomb repulsive H- • • • H$^-$ effects. The interesting nature of phase transition in {\em A}Ca(BH4)3 enters an unexplored field of weak interactions in ceramic-like host lattices and is the principal motivation for this study. Close di-hydrogen contacts suggest new concepts to tailor crystal symmetries in complex hydride perovskites in the future.}}, year = {2015} }