co-workers enable the use of Merrill-Basset-type DACs with standard-sized samples
on KOALA single-crystal diffractometer at ANSTO using Laue diffraction
[62]. These experimental parameters open up the possibility of probing materials
using neutron and X-ray techniques with the complementary information that they
provide. To achieve this, a miniaturised DAC had to be made from beryllium-copper
(BERYLCO-25) with necessary changes in design to support the pressure; however,
standard Boehler-Almax diamonds were used. The beryllium-copper design allowed
the cell to be fit and cooled in the cryostat on KOALA. Using hexamethylenetetramine and L-arginine dihydrate, the authors were able to demonstrate a high resolution and data completeness in the DAC (similar to one outside of the cell), and this
was due to the observation of reflections through the cell body that provided enough
data for anisotropic refinement at low temperatures. There are complications to the
method such as centring and the requirement for larger-sized sample crystals
(0.15 Â 0.20 Â 0.30 mm crystal was used in the study) lowering the maximum
achievable pressure to ~5 GPa; however, this method provides a basis from which
organic materials at high pressure can be explored using neutron diffraction.
2.3.2 Large Volume Presses
High pressure has been seen as a niche subject area for many years, but the strides
that have been made into the exploration of pharmaceutical materials have moved
this discussion onto industrial relevance of high pressure. Whilst much of the
crystallographic work has been performed using DACs and Paris-Edinburgh presses,
there have been developments in large volume equipment to investigate the formation and quenching of high-pressure phases for characterisation at ambient pressure.
Bridgman was the first to use large volume apparatus to investigate materials
under high pressure using a hydraulic press [18]. His efforts to design the cell that
would be able to make the measurements were not without its own hazards as he
noted in his paper ‘Finally, after six explosions, the attempt to use this form of
apparatus was entirely given up . . .’. Despite these setbacks he was able to build a
press that withstood the demands of pressure, and he began to build a legacy of
pressure measurements that is second to none in the field. His press was made from
two cylinders (upper and lower) connected by a heavy piece of tubing. The sample
was housed in the lower cylinder, whilst the pressure was applied to the upper
cylinder via a hydraulic press. The cylinder assembly was fitted with a micrometre so
that the distance of compression could be measured and coupled with the diameter of
the cylinder to assess the change in the volume of the sample; a manganin coil was
used to assess the pressure of the cell through a change in its resistance. During the
experiment the upper cylinder that contained the manganin coil was maintained at
35
C so that he did not need to worry about temperature effects on the resistance,
whilst the sample was housed in a separate thermostat to alter the temperature whilst
under load. To measure the melting points of the compounds, pressure was applied
to the sample beyond the freezing point of the sample before taking readings at
various pressures on decompression. To ensure that he characterised the melting line
Crystallography Under High Pressures
155
on KOALA single-crystal diffractometer at ANSTO using Laue diffraction
[62]. These experimental parameters open up the possibility of probing materials
using neutron and X-ray techniques with the complementary information that they
provide. To achieve this, a miniaturised DAC had to be made from beryllium-copper
(BERYLCO-25) with necessary changes in design to support the pressure; however,
standard Boehler-Almax diamonds were used. The beryllium-copper design allowed
the cell to be fit and cooled in the cryostat on KOALA. Using hexamethylenetetramine and L-arginine dihydrate, the authors were able to demonstrate a high resolution and data completeness in the DAC (similar to one outside of the cell), and this
was due to the observation of reflections through the cell body that provided enough
data for anisotropic refinement at low temperatures. There are complications to the
method such as centring and the requirement for larger-sized sample crystals
(0.15 Â 0.20 Â 0.30 mm crystal was used in the study) lowering the maximum
achievable pressure to ~5 GPa; however, this method provides a basis from which
organic materials at high pressure can be explored using neutron diffraction.
2.3.2 Large Volume Presses
High pressure has been seen as a niche subject area for many years, but the strides
that have been made into the exploration of pharmaceutical materials have moved
this discussion onto industrial relevance of high pressure. Whilst much of the
crystallographic work has been performed using DACs and Paris-Edinburgh presses,
there have been developments in large volume equipment to investigate the formation and quenching of high-pressure phases for characterisation at ambient pressure.
Bridgman was the first to use large volume apparatus to investigate materials
under high pressure using a hydraulic press [18]. His efforts to design the cell that
would be able to make the measurements were not without its own hazards as he
noted in his paper ‘Finally, after six explosions, the attempt to use this form of
apparatus was entirely given up . . .’. Despite these setbacks he was able to build a
press that withstood the demands of pressure, and he began to build a legacy of
pressure measurements that is second to none in the field. His press was made from
two cylinders (upper and lower) connected by a heavy piece of tubing. The sample
was housed in the lower cylinder, whilst the pressure was applied to the upper
cylinder via a hydraulic press. The cylinder assembly was fitted with a micrometre so
that the distance of compression could be measured and coupled with the diameter of
the cylinder to assess the change in the volume of the sample; a manganin coil was
used to assess the pressure of the cell through a change in its resistance. During the
experiment the upper cylinder that contained the manganin coil was maintained at
35
C so that he did not need to worry about temperature effects on the resistance,
whilst the sample was housed in a separate thermostat to alter the temperature whilst
under load. To measure the melting points of the compounds, pressure was applied
to the sample beyond the freezing point of the sample before taking readings at
various pressures on decompression. To ensure that he characterised the melting line
Crystallography Under High Pressures
155