Hydrothermally grown crystals of K8Nd3Si12O32(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) Å, b = 11.4550(10) Å, c = 11.6670(10) Å, α = 87.677(8)○, β = 87.491(9)○, γ = 79.083(8)○. 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. Refinement was carried out with 5667 independent and significant [I ≥ 2.5σ(I)] structure factors to a residual, R(F), of 0.047 (RW(F) = 0.057) using anisotropic temperature factors for all atoms. The structure, closely related to that of K8Yb3Si12O32(OH), is based on unusually flat Si12O32 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 "ideal" silicate layers of α-K3NdSi6O15·2H2O and β-K3NdSi6O15. 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 σ = [1.4×103 K/Ω/T]×exp(-0.8eV/kbT). Charge transport appears to occur by the motion of OH- ions.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry