A
model of Zincblende (ZnS), published in the Proceedings
of the Royal Institution in 1920
8.
Explaining Crystal Structure
Bragg
compared his new equation with the results that von
Laue's group had published. His explanation seemed far
more satisfying than von Laue's, as it didn't require
that only certain wavelengths be present.
In
one experiment, the group in Germany had rotated the
crystal by 3 degrees. The resulting X-ray diffraction
pattern had moved by 6 degrees. This is the expected
angle if the rays were reflecting off the crystal, so
confirming Bragg's theory that the diffraction could
be considered as reflection from planes in the crystal.
The
most satisfying result was on von Laue's photograph
of diffraction from zincblende crystals. Von Laue had
assumed that atoms in zincblende are arranged in a simple
cubic lattice, but if this was true Bragg's Law wouldn't
explain the diffraction pattern. But if the arrangement
of atoms was slightly different, arranged in a face centred cubic
lattice, the diffraction pattern was explained perfectly.
Not
only did Bragg's Law work, but it could be used to work
out how atoms are arranged inside a solid crystal!
