Chemistry Reference
In-Depth Information
reported previously in many materials were incorrect [
27
], and (2) the true struc-
tural behaviour of even simple elemental and binary systems at high pressures was
often extremely complex, and far more interesting than believed previously [
33
].
The development of ADXRD techniques was perfectly timed with regards to
the construction and commissioning of third generation synchrotron sources in the
mid-1990s. Such sources - the ESRF in Europe, the APS in the US and SPring-
8inJapan-were
ideally
suited to the new high-pressure ADXRD studies, by
providing extremely high-intensity, high-energy, microfocused, monochromatic
X-ray beams [
34
]. As a result, the new synchrotrons allowed high-pressure dif-
fraction to be pushed both to ever higher pressures and to more weakly-scattering
systems [
35
,
36
]. ADXRD techniques are now utilised routinely on high-pressure
beamlines around the world [
37
], and have been used by many different researchers
to study a wide range of materials such as the alkali metals [
38
-
42
], silicon [
43
],
scandium [
44
], phosphorus [
45
,
46
], titanium [
47
], gold [
48
], vanadium [
49
],
calcium [
50
], iodine [
51
], oxygen [
35
,
52
,
53
] and nitrogen [
54
,
55
]. In addition,
a large number of more complex materials of geological or technological interest
have also been studied, and ADXRD methods have been combined with laser
heating to enable structural studies to be carried out at extremes of pressure and
temperature [
56
-
59
].
Simultaneously with the developments in powder-diffraction techniques at
synchrotrons, high-quality single-crystal studies continued to be made on X-ray
laboratory sources during this period (see for example [
60
-
63
] and references
therein). And the availability of chemical crystallography beamlines on a number
of different synchrotrons around the world [
64
-
66
] was being exploited by
researchers in order to perform high-pressure single-crystal studies using these
machines, enabling ever more complex systems to be studied, including proteins
and other systems of biological and biochemical interest [
67
-
69
].
While the availability and intensity of X-ray sources, and the ease of compressing
suitably-small samples in DACs, has meant that X-ray diffraction techniques have
dominated high-pressure crystallography since the 1970s, powder and single-crystal
studies have continued to be conducted at neutron sources around the world, exploiting
the power of neutrons to probe H/D-containing materials [
70
,
71
], magnetism [
72
,
73
]
and phonons [
74
], or to make high real-space resolution studies of thermal motion [
75
].
Unfortunately, although such studies generally gave very high quality diffraction
data, and structural information that was, in many cases, superior to that obtainable
by X-ray methods, they were limited to much lower pressures, constrained by both
the relative weakness of neutron sources, and the large samples (tens of cubic
millimetres) therefore needed to obtain useable diffraction data. However, the
1990s saw a revolution in experimental methods that has greatly increased the
scope of high-pressure neutron diffraction. The advent of the compact Paris-Edinburgh
(P-E) press, first developed at the ISIS pulsed neutron (spallation) source in 1992 [
76
],
enabled neutron powder-diffraction structural studies to be pushed routinely to
above 25 GPa [
77
] while, more recently, full single-crystal data collection with
sufficient, and sufficiently-accurately measured, intensities for full structure refine-
ment has been extended to above 10 GPa [
78
].
