High Pressure Interest Group Seminar Series | Shull Wollan Center

High Pressure Interest Group Seminar Series

Title: High pressure neutron diffraction of small molecules

Speaker: Bernhard Massani, School of Physics and Astronomy, University of Edinburgh, UK

When: Thursday, May 23rd at 4:00 p.m.

Where: Bldg. 8630 Shull Wollan Center, Room A-202

Seminar Series: High Pressure Interest Group

Abstract:

In my thesis I want to shed light on various hydrogen rich systems - from H-bonded gas hydrates to pure hydrogen - under the influence of pressure using neutron diffraction. Here I would like to present data on a (low pressure) study of the recently found sX hydrate/ice XVII system [1,2]. This structure is unique in a sense that it is so far the only gas hydrate with chiral channels. It is formed by hydrogen-water or carbon dioxide-water mixtures at pressures above 0.3 GPa and it has been shown that it is the only clathrate hydrate that is refillable with hydrogen [3]. I will show that sX is also refillable with other gases, e.g. nitrogen. This property makes it a possible storage material for gases [4].

Furthermore, I want to show the possibilities for single-crystal neutron diffraction (SCND) at ORNL:  While neutron diffraction for systems at relatively low pressures (up to 30 GPa) is well established, higher pressures remain still hard to achieve and require the use of diamond anvil cells (DACs). Only recently the latter became suitable for neutron diffraction due to the commercial production of larger diamonds. This technique has - so far - mainly been used for powder diffraction, and as such has its limits [5].  For many systems, single-crystal techniques are critical in that they provide a much higher real-space resolution enabling access to short d-space Bragg reflections that would be heavily overlapped in a powder study – a problem that could be avoided diffracting of single crystals rather than powder. However, quantitative SCND studies under high pressure remain challenging, and the full possibilities of the approach are almost completely untested. I will show preliminary results of a trial experiments carried out on SNAP and TOPAZ to benchmark these instruments for SCND and to investigate the relationship between sample volume and data quality.

  1. H. Hirai et al., J. Chem. Phys. (2011), 133, 124511
  2. V. Efimchenko et al., All . Comp. (2011), 509(2), 860-863
  3. D. Amos et al., J. Phys. Chem. (2018), 8, 4295-4299
  4. B. Massani et al., JCP. (2019) – accepted
  5. R. Boehler et al.,  Rev. Sci. Inst. (2017), 88, 08390

Host: Bianca Haberl

Cell: (865)805 4065

Date: 

Thursday, May 23, 2019 - 16:00 to 17:00

Speaker Name: 

Bernhard Massani, School of Physics and Astronomy, University of Edinburgh, UK

Location: 

Shull Wollan Center (ORNL Bldg. 8630), Room A202

Host: 

Bianca Haberl

Event Type: