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Structural Variations in the Solid‐Solution Series Ln x Ca 2−x Al[Al 1+x Si 1−x O 7 ] with 0 ≤ x ≤ 1 and Ln = La, Eu, Er
Author(s) -
Peters Lars,
Knorr K.,
Depmeier W.
Publication year - 2006
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.200500361
Subject(s) - gehlenite , melilite , crystallography , solid solution , bar (unit) , chemistry , rietveld refinement , molar ratio , type (biology) , crystal structure , materials science , physics , phase (matter) , metallurgy , geology , biochemistry , organic chemistry , spinel , catalysis , paleontology , meteorology
Gehlenite, Ca 2 Al[AlSiO 7 ], has melilite‐type structure with space group $P{\bar 4}{\rm 2}{\rm _{1}}m$ . It contains two topologically distinct positions coordinated tetrahedrally by oxygen. One is completely occupied by Al 3+ , whereas the other one contains Al 3+ and Si 4+ . Normally, the Al 3+ molar fraction in the second tetrahedrally coordinated position does not exceed x Al = 0.5, i.e. the so‐called Loewenstein ‐rule is obeyed. In this contribution the structural variations in the melilite‐type compounds of the compositions La x Ca 2−x Al[Al 1+x Si 1−x O 7 ], Eu x Ca 2−x Al[Al 1+x Si 1−x O 7 ] and Er x Ca 2−x Al[Al 1+x Si 1−x O 7 ] are discussed. All members of the solid solution except the end‐members violate Loewenstein 's rule. Rietveld refinements against X‐ray powder diffraction patterns confirm that the compounds have space group $P{\bar 4}{\rm 2}{\rm _{1}}m$ , without changes in the Wyckoff ‐positions of the ions compared to gehlenite.