The crystal structures of phenacite-type Li2(MoO4), and scheelite-type LiY(MoO4)2 and LiNd(MoO4)2
- Author(s)
- Uwe Kolitsch
- Abstract
The crystal structures of flux-grown Li2(MoO4), LiY(MoO4)2 and LiNd(MoO4)2 were solved and refined from single-crystal intensity data collected with a four-circle diffractometer (MoKa X-radiation, CCD area detector, room temperature). Li2(MoO4) is isostructural with phenacite, Be2(SiO4) and has space group R3¯, a = 14.330(2), c = 9.584(2) A°, Z= 18 (R1 = 1.6%). The structure consists of a three-dimensional network of corner-linked, slightly distorted LiO4 and fairly regular MoO4 tetrahedra. Average Li-O and Mo-O distances are 1.965 A° (Li1) and 1.967 A° (Li2), and 1.764 A° (Mo). The atomic arrangement is characterised by a narrow open channel along the three-fold axis. Comparisons are drawn with other phenacite-type compounds. Low-temperature single-crystal X-ray studies of Li2(MoO4) in the range from 103 to 293 K gave no evidence of a phase transition, thus contradicting recent literature reports. Both LiY(MoO4)2 and LiNd(MoO4)2 crystallise in the scheelite-type structure, with space group I41/a and Z = 2 (R1 = 1.7 and 2.7%, respectively). The first has a = 5.148(1), c = 11.173(2) A°, V= 296.11(10) A°3, the latter a = 5.243(1), c = 11.440(2) A°, V= 314.47(10) A°3. Both Li and Y/Nd are completely disordered on a jointly occupied site. Mean (Y,Li)- and (Nd,Li)-O distances are 2.40 and 2.47 A°, respectively. In both compounds the unique MoO4 tetrahedron has four identical Mo-O bonds with lengths of 1.779 A°. The stoichiometry of LiRE(MoO4)2 (RE = rare-earth element) compounds is discussed and the relation to structure types of other MRE(XO4)2 (M = alkali metal, X = Mo, W) compounds is briefly addressed.
- Organisation(s)
- Department of Mineralogy and Crystallography
- Journal
- Zeitschrift für Kristallographie : international journal for structural, physical, and chemical aspects of crystalline materials
- Volume
- 216
- Pages
- 449-454
- No. of pages
- 6
- ISSN
- 0044-2968
- Publication date
- 2001
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 1051 Geology, Mineralogy
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/46f90bb5-2418-4d02-a4fc-2ff4fb290efc