Open AccessNew phosphate langbeinites, K 2 M Ti(PO 4 ) 3 ( M = Er, Yb or Y), and an alternative description of the langbeinite framework
Author(s) -
Norberg Stefan T.
Publication year - 2002
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
eISSN - 1600-5740
pISSN - 0108-7681
DOI - 10.1107/s0108768102013782
Subject(s) - isostructural , crystallography , octahedron , potassium , rare earth , crystal structure , chemistry , phosphate , potassium phosphate , chromium , titanium , space group , mineralogy , materials science , x ray crystallography , diffraction , physics , organic chemistry , chromatography , optics
Three new potassium rare‐earth/titanium phosphate structures, K 2 ErTi(PO 4 ) 3 (KErTP), K 2 YbTi(PO 4 ) 3 (KYbTP) and K 2 YTi(PO 4 ) 3 (KYTP), are presented, all of which are characterized by single‐crystal X‐ray diffraction studies. In addition, a fourth structure, K 2 CrTi(PO 4 ) 3 (KCrTP), has been reinvestigated. All structures are isostructural to the langbeinite‐type structure and result from changes made to the growth constituents in high‐temperature flux‐growth experiments intended to give structurally modified potassium titanyl phosphate (KTP). The two crystallographically independent octahedra sites (site symmetry 3) have a mixed Ti/ M ( M = Er, Yb, Y or Cr) population, although the rare‐earth metals favour one site while chromium favours the other. An alternative approach for the description of the channels and cation cages in langbeinite and related structures is given using [ M 5 X 6 O 39 ] units. The framework of langbeinite is compared with that of nasicon using these alternative building units. All of the investigated structures crystallize in space group P 2 1 3 with Z = 4; a = 10.1053 (2) Å, R = 0.023 (KErTP); a = 10.0939 (8) Å, R = 0.022 (KYbTP); a = 10.1318 (6) Å, R = 0.047 (KYTP); a = 9.8001 (2) Å, R = 0.016 (KCrTP).