Chemistry Reference
In-Depth Information
a
D
D
D
D
D
D
D
D
D
D
b
2
θ
(deg.)
5
10
15
20
25
Fig. 4 (a) 2D diffraction pattern collected from a polycrystalline sample of orthorhombic Pr-VII
at a pressure of 19 GPa [
145
]. The data were collected in a 2 s exposure on beamline ID09 at the
ESRF synchrotron, during which the diamond anvil pressure cell was oscillated
9
to improve
the powder averaging. This large oscillation angle resulted in the appearance of a number of Bragg
reflections (marked with a D) from the anvils of the pressure cell. (b) The resulting 1D diffraction
profile, after azimuthal integration of the 2D pattern using Fit2D [
161
]. The diamond reflections
were omitted from the integration
The ability to collect the full 2D diffraction profiles had an additional, but
unexpected, benefit. In studies of the III-V semiconductor InSb, it became imme-
diately clear that samples which were very good powders when loaded, giving
smooth D-S rings, could sometimes recrystallise at high pressure, giving very
“spotty” diffraction patterns [
164
]. However, the later discovery that this phenom-
enon was relatively widespread led to more systematic use of it to identify phases
that might be grown as single-crystals at high pressure simply by compression at
room temperature, rather than by growing crystals from the melt. The prospect thus
opened up of single-crystal studies beyond the first-order phase transitions that had
been thought to prohibit such studies. The exact “recipe” for growing a useful single
