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Incommensurately modulated twin structure of nyerereite Na 1.64 K 0.36 Ca(CO 3 ) 2
Author(s) -
Bolotidezhda B.,
Gavryushkin Pavel N.,
Korsakov Andrey V.,
Rashchenko Sergey V.,
Seryotkin Yurii V.,
Golovin Alexander V.,
Moine Bertrand N.,
Zaitsev Anatoly N.,
Litasov Konstantin D.
Publication year - 2017
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520616020680
Subject(s) - orthorhombic crystal system , crystallography , crystal structure , chemistry , modulation (music) , group (periodic table) , physics , condensed matter physics , organic chemistry , acoustics
The incommensurately modulated twin structure of nyerereite Na 1.64 K 0.36 Ca(CO 3 ) 2 has been first determined in the (3 + 1)‐dimensional symmetry group Cmcm (α00)00 s with modulation vector q = 0.383 a *. Unit‐cell values are a = 5.062 (1), b = 8.790 (1), c = 12.744 (1) Å. Three orthorhombic components are related by threefold rotation about [001]. Discontinuous crenel functions are used to describe the occupation modulation of Ca and some CO 3 groups. The strong displacive modulation of the O atoms in vertexes of such CO 3 groups is described using x‐harmonics in crenel intervals. The Na, K atoms occupy mixed sites whose occupation modulation is described in two ways using either complementary harmonic functions or crenels. The nyerereite structure has been compared both with the commensurately modulated structure of K‐free Na 2 Ca(CO 3 ) 2 and with the widely known incommensurately modulated structure of γ‐Na 2 CO 3 .