TY - JOUR

T1 - N-2-O-2 icing in single-crystal in-house X-ray diffraction experiments using an open-flow helium cryostat

AU - Zakharov, Boris A.

AU - Miletich, Ronald

AU - Bogdanov, Nikita E.

AU - Boldyreva, Elena

N1 - Funding Information: NEB, BAZ and EVB acknowledge support by the Ministry of Science and Higher Education of Russia. The work was carried out jointly by the Boreskov Institute of Catalysis (project AAAA-A21-121011390011-4) and Novosibirsk State University. RM acknowledges the support of the University of Vienna (grant No. BE532003) and the Austrian Science Foundation (FWF, grant No. P 29149-N29). Publisher Copyright: © 2021.

PY - 2021/8/1

Y1 - 2021/8/1

N2 - This note reports a study of the coating of a crystal with 'ice' at temperatures below 45 K during single-crystal in-house diffraction experiments when using an open-flow helium cryostat. The 'ice' consists mainly of crystalline oxygen and nitrogen. This suggests completely different techniques for avoiding this type of icing compared with water icing. With appropriate choices of crystal mount, crystal position with respect to the nozzle and gas flow conditions, it is possible to avoid detectable condensation. However, sometimes this cannot be achieved in practice (poor diffraction from a smaller crystal, necessity of positioning the crystal in certain orientations to achieve desired data completeness, need to reduce helium consumption etc.). The problem of icing seems to be less common for powder experiments where the laminar gas flow is parallel to the capillary containing the sample, and for synchrotron experiments where the sample is comparatively small and almost continuously rotated, which facilitates the ice covering being removed by the gas flow. This last technique can in principle also be applied to single-crystal X-ray diffraction using laboratory diffractometers - periodic rapid rotation of the crystal can help to minimize any icing, but this technique will not work when the condensation rate is comparable to or faster than one frame of data collection. The coating around a sample crystal reduces the quality of the diffraction data, and the temperature at the sample below the coating may differ significantly from that at the cryostat nozzle reported by the instrument.

AB - This note reports a study of the coating of a crystal with 'ice' at temperatures below 45 K during single-crystal in-house diffraction experiments when using an open-flow helium cryostat. The 'ice' consists mainly of crystalline oxygen and nitrogen. This suggests completely different techniques for avoiding this type of icing compared with water icing. With appropriate choices of crystal mount, crystal position with respect to the nozzle and gas flow conditions, it is possible to avoid detectable condensation. However, sometimes this cannot be achieved in practice (poor diffraction from a smaller crystal, necessity of positioning the crystal in certain orientations to achieve desired data completeness, need to reduce helium consumption etc.). The problem of icing seems to be less common for powder experiments where the laminar gas flow is parallel to the capillary containing the sample, and for synchrotron experiments where the sample is comparatively small and almost continuously rotated, which facilitates the ice covering being removed by the gas flow. This last technique can in principle also be applied to single-crystal X-ray diffraction using laboratory diffractometers - periodic rapid rotation of the crystal can help to minimize any icing, but this technique will not work when the condensation rate is comparable to or faster than one frame of data collection. The coating around a sample crystal reduces the quality of the diffraction data, and the temperature at the sample below the coating may differ significantly from that at the cryostat nozzle reported by the instrument.

KW - helium open-flow cryostat

KW - cryocrystallography

KW - single-crystal X-ray diffraction

KW - icing

KW - RADIATION-DAMAGE

KW - CRYSTALLOGRAPHY

UR - http://www.scopus.com/inward/record.url?scp=85120962822&partnerID=8YFLogxK

U2 - 10.1107/S1600576721006440

DO - 10.1107/S1600576721006440

M3 - Article

VL - 54

SP - 1271

EP - 1275

JO - Journal of Applied Crystallography

JF - Journal of Applied Crystallography

SN - 0021-8898

ER -