Neutron Diffraction of Large-Volume Samples at High Pressure Using Compact Opposed-Anvil Cells

Neutron diffraction techniques of large-volume samples at high pressure using compact opposed-anvil cells are developed at a reactor neutron source, China's Mianyang research reactor. We achieve a high-pressure condition of in situ neutron diffraction by means of a newly designed large-volume opposed-anvil cell. This pressure calibration is based on resistance measurements of bismuth and the neutron diffraction of iron. Pressure calibration experiments are performed at room temperature for a new cell using the tungsten carbide anvils with a tapered angle of 30^\circ, \it \Phi4.5 mm culet diameter and the metal-nonmetal composite gasket with a thickness of 2 mm. Transitions in Bi (I–II 2.55 GPa, III–V 7.7 GPa) are observed at 100 and 300 kN, respectively, by resistance measurements. The pressure measurement results of neutron diffraction are consistent with resistance measurements of bismuth. As a result, pressures up to about 7.7 GPa can routinely and stably be achieved using this apparatus, with the sample volume of 9 mm^3.