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Structure, phase transitions and ionic conductivity of K_3NdSi_6O_(15)·xH_2O. II. Structure of β-K_3NdSi_6O_(15)

Haile, S. M. and Wuensch, B. J. (2000) Structure, phase transitions and ionic conductivity of K_3NdSi_6O_(15)·xH_2O. II. Structure of β-K_3NdSi_6O_(15). Acta crystallographica. Section B, Structural science, 56 (3). pp. 349-362. ISSN 0108-7681. doi:10.1107/S0108768199015797.

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Hydrothermally grown crystals of β-K_3NdSi_6O_(15), potassium neodymium silicate, have been studied by single-crystal X-ray methods. Under appropriate conditions, the compound crystallizes in space group Bb2_1m and has lattice constants a = 14.370 (2), b = 15.518 (2) and c = 14.265 (2) Å. There are 30 atom sites in the asymmetric unit of the basic structure. With eight formula units per unit cell, the calculated density is 2.798 Mg m^(-3). Refinement was carried out to a residual, wR(F^2), of 0.1177 [R(F) = 0.0416] using anisotropic temperature factors for all atoms. The structure is based on (Si_2O_5^(2-))∞ layers, connected by Nd polyhedra to form a three-dimensional framework. Potassium ion sites, some of which are only partially occupied, are located within channels that run between the silicate layers. The silica-neodymia framework of β-K_3NdSi_6O_(15), in particular the linkages formed between the silicate layers and Nd polyhedra, bears some similarities to that of the essentially isocompositional phase α-K_3NdSi_6O_(15)·2H_2O. In both, the silicate layers are corrugated so as to accommodate a simple cubic array of NdO_6 octahedra with lattice constant 7.5 Å. Furthermore, the Si_2O_5 layers in β-K_3NdSi_6O_(15) are topologically identical to those of the mineral sazhinite, Na_2HCeSi_6O_(15). Although β-K_3NdSi_6O_(15) and sazhinite are not isostructural, the structures of each can be described as slight distortions of a high-symmetry parent structure with space group Pbmm.

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Haile, S. M.0000-0002-5293-6252
Additional Information:© 2000 International Union of Crystallography. Received 12 May 1999; Accepted 6 December 1999. The authors are grateful to Karl Peters of the Max Planck Institut für Festkörperforschung for collecting single-crystal intensity data. Steve Recca of the Massachusetts Institute of Technology kindly carried out microprobe analyses. SMH thanks Joachim Maier for hosting her visit at MPI, where some portions of this research were carried out. This work is dedicated to the memory of the late Robert A. Laudise, a brilliant scientist and exemplary human being who provided invaluable guidance in the method of hydrothermal synthesis. His friendship and inspiration are greatly missed by those who were fortunate to know him.
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Record Number:CaltechAUTHORS:20160913-121404206
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Official Citation:Haile, S. M. & Wuensch, B. J. (2000). Acta Cryst. B56, 349-362
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:70309
Deposited By: Tony Diaz
Deposited On:13 Sep 2016 23:19
Last Modified:11 Nov 2021 04:27

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