TY - JOUR
T1 - Structure determination of a low temperature phase of calcium and strontium amide by means of neutron powder diffraction on Ca(ND2)2 and Sr(ND2)2
AU - Senker, J.
AU - Jacobs, H.
AU - Müller, M.
AU - Press, W.
AU - Mayer, H. M.
AU - Ibberson, R. M.
PY - 1999
Y1 - 1999
N2 - Calcium and Strontium amide are ionic compounds crystallising in a tetragonally distorted anatase structure-type at ambient temperatures. The amide ions (NH27 ND2-) resemble water molecules in structure and in charge distribution. By means of temperature dependent neutron diffraction investigations weak super-structure reflections were observed at temperatures below 90 K (Ca(ND2)2) and 60 K (Sr(ND2)2), respectively, indicating the existence of a so far unknown low-temperature (LT) phase. Using high resolution neutron powder diffraction at temperatures below 10 K the structure was determined for both compounds. The LT-phases are isotypic and crystallise monoclinic in the space group P21/c with four formula units within the unit cell: Ca(ND2)2 at 10 K a = 7.257(2) Å, b = 7.2434(2) Å, c = 6.300(1) Å, β = 124.73(1)o Sr(ND2)2 at 5 K a = 7.6950(1) Å, b = 7.68374(9) Å, c = 6.6324(3) Å, β = 124.917(2)o. Their structure is closely related to the tetragonal HT-phase, but an ordering of the amide ions occurs due to freezing of a lattice mode which is dominated by the librational motion of the amide ions in the {1 0 0} planes of the HT-phase.
AB - Calcium and Strontium amide are ionic compounds crystallising in a tetragonally distorted anatase structure-type at ambient temperatures. The amide ions (NH27 ND2-) resemble water molecules in structure and in charge distribution. By means of temperature dependent neutron diffraction investigations weak super-structure reflections were observed at temperatures below 90 K (Ca(ND2)2) and 60 K (Sr(ND2)2), respectively, indicating the existence of a so far unknown low-temperature (LT) phase. Using high resolution neutron powder diffraction at temperatures below 10 K the structure was determined for both compounds. The LT-phases are isotypic and crystallise monoclinic in the space group P21/c with four formula units within the unit cell: Ca(ND2)2 at 10 K a = 7.257(2) Å, b = 7.2434(2) Å, c = 6.300(1) Å, β = 124.73(1)o Sr(ND2)2 at 5 K a = 7.6950(1) Å, b = 7.68374(9) Å, c = 6.6324(3) Å, β = 124.917(2)o. Their structure is closely related to the tetragonal HT-phase, but an ordering of the amide ions occurs due to freezing of a lattice mode which is dominated by the librational motion of the amide ions in the {1 0 0} planes of the HT-phase.
KW - Alkaline earth metal amides
KW - Antiferro distortive ordering
KW - Calcium amide
KW - Neutron diffraction
KW - Strontium amide
KW - Structure of low temperature modification
UR - https://www.scopus.com/pages/publications/0040320200
U2 - 10.1002/(SICI)1521-3749(199912)625:12<2025::AID-ZAAC2025>3.0.CO;2-3
DO - 10.1002/(SICI)1521-3749(199912)625:12<2025::AID-ZAAC2025>3.0.CO;2-3
M3 - Article
AN - SCOPUS:0040320200
SN - 0044-2313
VL - 625
SP - 2025
EP - 2032
JO - Zeitschrift fur Anorganische und Allgemeine Chemie
JF - Zeitschrift fur Anorganische und Allgemeine Chemie
IS - 12
ER -