Chapter 23 - Development of high P-T neutron diffraction at LANSCE—toroidal anvil press, TAP-98, in the HiPPO diffractometer

Abstract

This chapter discusses the technical issues related to press design, pressure-temperature (P-T) control, translation stage, diffraction optics, anvil package, and cell assembly. The development of neutron diffraction under extreme pressure and temperature conditions is highly valuable to condensed matter physics, crystal chemistry, materials sciences, as well as the Earth and planetary sciences. A 500-ton press, TAP-98 (Toroidal Anvil Press, designed in 1998) is included into the High-Pressure and Preferred-Orientation (HiPPO) diffractometer at Los Alamos Neutron Science Center (LANSCE) to conduct in situ high P-T neutron diffraction experiments. The HiPPO diffractometer takes advantage of the improved spallation neutron source at LANSCE and a short flight path to achieve a neutron flux of 108 n/cm2/s at the sample, nominally. The new HiPPO beam-line increases more than five times the detector area for the 90° diffraction banks (used mostly for high-pressure experiments) as compared to the old High Intensity Powder Diffractometer beam-line. This chapter aims to accurately map lattice parameters, thermal parameters, bond lengths, bond angles, neighboring atomic environments, and phase stability in P-T-X space. Studies based on high-pressure neutron diffraction are important for multidisciplinary science. Additional equipment for in situ high P-T neutron diffraction is being designed and tested.