The Structure and Conductivity of K8Nd3Si12O32(OH): A Layered Silicate with Paths for Possible Fast-Ion Condution
✍ Scribed by S.M Haile; B.J Wuensch; T Siegrist
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 469 KB
- Volume
- 148
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
Hydrothermally grown crystals of K 8 Nd 3 Si 12 O 32 (OH) have been examined by single crystal X-ray methods. The compound crystallizes in space group P1 and has lattice constants a ؍ 6.9660(6) A s , b ؍ 11.4550(10) A s , c ؍ 11.6670(10) A s , ؍ 87.677(8)3, ؍ 87.491(9)3, ؍ 79.083(8)3. There are 29 nonhydrogen atoms in the asymmetric unit. With one formula unit per unit cell, the calculated density is 2.929 Mg m ؊3 . Re5nement was carried out with 5667 independent and signi5cant [ I52.5 (I )] structure factors to a residual, R(F ), of 0.047 (R w (F ) ؍ 0.057) using anisotropic temperature factors for all atoms. The structure, closely related to that of K 8 Yb 3 Si 12 O 32 (OH), is based on unusually 6at Si 12 O 32 layers that are connected by Nd octahedra to form a three-dimensional framework. The silicate layer contains two types of six-membered rings, an eight-membered ring, and a meandering twelve-membered ring. It can be generated from a condensation of wollastonite-type chains and contains structural features found in the 99ideal:: silicate layers of -K 3 NdSi 6 O 15 ' 2H 2 O and -K 3 NdSi 6 O 15 . Potassium ions are located in the interstitial sites of the neodymia+silica framework, in channels that run between silicate layers; hydroxyl groups reside within channels that run through the layers. The conductivity in the [0 1 0] direction is given by ؍ [1.4؋10 3 K/ cm/T ]؋exp (؊0.8 eV/k b T ). Charge transport appears to occur by the motion of OH ؊ ions.