Neutron powder diffraction of small-volume samples at high pressure using compact opposed-anvil cells and focused beam

Neutron powder diffraction techniques of small-volume samples at high pressure using compact opposed-anvil cells were developed at J-PARC pulsed neutron source. For this purpose we apply a few types of super-hard materials as opposed anvils with culet diameters between 3 to 5 mm. Generated pressures with these anvils were up to 9 GPa for 2 to 4 mm³ and up to 14 GPa for 0.7 mm³ sample volumes, which not only depends on the anvil geometry and material but even more depends on the metallic gasket geometry and material. A representative anvil geometry with 4 mm in culet diameter, along with TiZr "null alloy" metallic gasket containing varying sample volumes, were then applied to time-of-flight neutron powder diffraction experiments, where methane hydrate of 4 mm³ volume and lead of 0.7 mm³ volume were separately measured and their signal-to-background ratios were evaluated. A neutron-focusing optics was used to concentrate the neutron beam into these small-volume samples to increase the intensity of diffraction. Although spurious diffraction peaks from the anvils were prominent, more than seven diffraction peaks are clearly observed from both of the samples. In spite of the smaller sample capacity than previous standard high-pressure apparatus for neutron, it is concluded that the opposed-anvil cells will become alternative apparatuses for neutron scattering at strong pulsed neutron sources where sufficient neutron intensity was granted.