0000000000285978
AUTHOR
Ekkehart Tillmanns
Bellbergite?a new mineral with the zeolite structure type EAB
The new mineral bellbergite, (K, Ba, Sr)2Sr2Ca2(Ca, Na)4Al18Si18O72 · 30H2O, has been found in Ca-rich xenoliths at the Bellberg volcano near Mayen, Eifel, Germany. It occurs as well formed bipyramids with a length up to 0.3 mm. Possible space groups are P63/mmc, P62c and P63mc with a = 13.244(1) A, c = 15.988(2) A, V = 2429 A3, Z = 1. The density is: Dm, = 2.20(2) Mg/m3, Dc = 2.19 Mg/m3. The empirical formula based on 72 oxygen atoms is: Ba0.26Na0.72K1.33Sr2.36Ca5.32Al17.55Si18.36O72 · 30H2O. The mineral is uniaxial negative with ω = 1.522(2) and e = 1.507(2) (λ = 589 nm). The strongest lines in the X-ray powder pattern are (d (A), I, hkl): 3.80 (100) (300, 212, 104), 6.58 (80) (102), 2.95…
Crystal Structure of the Microwave Dielectric Resonator Ba2Ti9O20
A single-crystal X-ray study of dibarium nonatitanate, Ba2Ti9O20, yielded the triclinic space group P 1 with a=0.7471(1), b= 1.4081(2), c= 1.4344(2) nm, α=89.94(2)°, β= 79.43(2)°, γ= 84.45(2)°, V = 1.476 nm3 Z = 4, and Dx= 4.61 Mg/m3. A refinement of atomic coordinates and isotropic thermal parameters led to a residual of 0.03. The structure consists of hexagonally closest-packed layers of Ba and O atoms in the sequence (hch)3. All Ti atoms reside in octahedral interstices of this closest packing. The various Ti coordination octahedra share only edges and corners with each other. One-half of the Ba atoms is twelve-coordinated by oxygen atoms, the other half is eleven-coordinated.
ChemInform Abstract: Crystal Structure of the Microwave Dielectric Resonator Ba2Ti9O20.
A single-crystal X-ray study of dibarium nonatitanate, Ba2Ti9O20, yielded the triclinic space group P 1 with a=0.7471(1), b= 1.4081(2), c= 1.4344(2) nm, α=89.94(2)°, β= 79.43(2)°, γ= 84.45(2)°, V = 1.476 nm3 Z = 4, and Dx= 4.61 Mg/m3. A refinement of atomic coordinates and isotropic thermal parameters led to a residual of 0.03. The structure consists of hexagonally closest-packed layers of Ba and O atoms in the sequence (hch)3. All Ti atoms reside in octahedral interstices of this closest packing. The various Ti coordination octahedra share only edges and corners with each other. One-half of the Ba atoms is twelve-coordinated by oxygen atoms, the other half is eleven-coordinated.