AP Seminar - Developing Neutron Techniques at Extreme Conditions: the High Pressure Neutron Diffractometer at China Spallation Neutron Source (CSNS)

The development of neutron techniques under extreme conditions is invaluable to condensed matter physics, crystal chemistry, materials science, and earth and planetary sciences. In situ neutron diffraction experiments at high-pressures (HP) provide unique opportunities to investigate materials under these harsh conditions. As one of the cornerstone research platforms within the Shenzhen Materials Genome Large-Scale Facilities project, the high-pressure neutron diffractometer has been designated as Beamline BL-15 at CSNS and is currently callibrating HP sample enviroments with neutrons by the Southern University of Science and Technology (SUSTech) and CSNS. The beamline is expected to be commissioned in 2025, with neutron diffraction and imaging as its primary techniques in conjunction with various sample environments under extreme conditions. Its main design parameters are as follows: 1) the d-spacing range (90° detector in the single frame mode): 0.5 – 5 Å; 2) the resolution: Δd/d ≤ 0.6% (90° detector); and 3) the neutron flux at the sample position: > 5 × 10⁶ n/s/cm² @ 100 kW. The extreme sample environments include: 1) high-pressure (P) and temperature (T) [P (max) = 20 GPa, T (max) = 1300 K); 2) low-T and high magnetic field [B (max) = 9 T, T (min) = 4 K]; and 3) high-P percolation (pore pressure ≤ 150 MPa, confining pressure ≤ 200 MPa, deviatoric stress ≤ 300 MPa, and sample temperature: 270 K ≤ T ≤ 370 K). The high penetrating power of neutrons presents great advantages in designing pressure cells with various types of high strength metals, alloys, and ceramics. A suite of pressure devices, such as true triaxial multi-anvil press, piston cylinder, P-E cell, gas/liquid high-P cell, portable cubic press, and ZAP cell, etc., will be used to provide extreme P-T conditions and the flexibility of switching experimental systems between the portable and transferable devices. The high-P facility is augmented by simultaneous multi-mode in situ measurements for physical parameters such as mechanic, thermal, acoustic, optical, and electrical properties under extreme conditions.

High-P neutron facility at CSNS will provide scientists with a new venue to carry out frontier interdisciplinary research under comprehensive extreme sample environments of high pressure, high/low temperature, and/or high magnetic field. Similar techniques have been successfully used to study the equations of state, structural phase transitions, and thermomechanical properties of metals, ceramics, and minerals. We have previously conducted researches using neutron diffraction technique on the formation/decomposition kinetics of methane, CO2 and hydrogen hydrate clathrates, and hydrogen/CO2 adsorption of inclusion compounds such as metal–organic frameworks (MOFs). High-P neutron facility at CSNS is expected to have a positive impact on the basic science research in physics, chemistry, materials science, energy science, and earth and planetary sciences, and therefore create ample opportunities for new discoveries in science and technology.