The fundamental structure perpendicular to the c-axis starts with a honeycomb lattice. In each honeycomb cell of the lattice, a subunit is placed. There are three kinds of subunits, and near the vertices of the honeycomb lattice 4th subunit consisting of a chain of 4 atoms is placed.
Take a unit cell as follows. Picking one of the hexagons of the lattice, inset a subunit 1 as defined below. In the six adjoining hexagons, place alternately subunits 2a and 2b as shown below. This fundamental pattern, with subunit one surrounded by set of three each of subunits 2a and 2b, form most of the crystal structure. The atom chains, denoted unit 3 below, are placed close to the vertices of a honeycomb lattice.
The crystal structure can be visualized along the c-axis a as a decorated honeycomb lattice.
Mine | Xray | x | y | z | (n-fold) | |
Be 18 | Be 12 | 0.124 | 0.248 | 1.000 | (3) | |
Be 17 | Be 11 | 0.000 | 0.000 | 0.893 | ||
B 6 | B 4 | 0.000 | 0.188 | 0.812 | (6) | |
Be 13 | Be8 | 0.238 | 0.118 | 0.642 | (3) | |
B 12 | B 8 | 0.118 | 0.238 | 0.642 | (3) | |
B 11 | B 7 | 0.062 | 0.124 | 0.500 | (3) | |
B 12 | B 8 | 0.119 | 0.238 | 0.358 | (3) | |
Be 13 | Be 8 | 0.238 | 0.118 | 0.358 | (3) | |
B 6 | B 4 | 0.000 | 0.188 | 0.188 | (6) | |
Be 17 | Be 11 | 0.000 | 0.000 | 0.107 | ||
Be 18 | Be 12 | 0.124 | 0.248 | 0.000 | (3) |
This unit, contains 5 Be and 24 B atoms, and is shown in this VRML file.
Mine | Xray | x | y | z | (n-fold) about (2/3,1/3,z) |
B 2 | B 1 | 0.493 | 0.164 | 1.00 | (6) |
Be 19 | Be 13 | 2/3 | 1/3 | 0.875 | |
B 5 | B 3 | 0.552 | 0.105 | 0.847 | (3) |
B 8 | B 5 | 0.506 | 0.210 | 0.693 | (3) |
B 10 | B 6 | 0.458 | 0.228 | 0.595 | (3) |
Be 15 | Be 9 | 0.560 | 0.440 | 0.500 | (3) |
B 10 | B 6 | 0.458 | 0.228 | 0.405 | (3) |
B 8 | B 5 | 0.506 | 0.210 | 0.307 | (3) |
B 5 | B 3 | 0.552 | 0.105 | 0.153 | (3) |
Be 19 | Be 13 | 2/3 | 1/3 | 0.125 | |
B 2 | B 1 | 0.493 | 0.164 | 0.000 | (6) |
Unit 2b is same as unit 2a, except Be sites at z=0.125, 0.875 are absent. The coordinates are obtained by switching x and y in table for Unit 2a.
Unit 3 (a vertical column of 4 atoms -- see VRML) sits roughly at the midpoint of the triangle whose vertices are at the centers of the Unit 1, Unit 2a and Unit 2b objects, or equivalently near the vertices of the hexagonal lattice whose openings contain the 1 and 2 subunits. There is a six-fold axis around (0,0,z) yielding six equivalent sites. This third unit could also be attached to the hexagonal corners of Unit 1, but it makes seeing Unit 1 difficult.
Mine | Xray | x | y | z |
B 3 | B 2 | 0.348 | 0.000 | 0.905 |
Be 16 | Be 10 | 0.364 | 0.000 | 0.679 |
Be 16 | Be 10 | 0.364 | 0.000 | 0.321 |
B 3 | B 2 | 0.348 | 0.000 | 0.095 |
Be29 B81 corresponds to putting only Unit 2a's at the vertices of the honeycomb lattice. Be31 B81 corresponds to Unit 2a's at half of the honeycomb lattice and Unit 2b's on the other half. Be33 B81 would have all Unit 2b's on the honeycomb lattice