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Negative X-ray expansion in cadmium cyanide

DOI: 10.1039/D0MH01989E DOI Help

Authors: Chloe S. Coates (University of Oxford; University of Cambridge) , Claire A. Murray (Diamond Light Source) , Hanna L. B. Bostroem (University of Oxford; Max Planck Institute for Solid State Research) , Emily M. Reynolds (University of Oxford; ISIS Facility) , Andrew L. Goodwin (University of Oxford)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Materials Horizons , VOL 66

State: Published (Approved)
Published: February 2021
Diamond Proposal Number(s): 18786 , 17375

Open Access Open Access

Abstract: Cadmium cyanide, Cd(CN)2, is a flexible coordination polymer best studied for its strong and isotropic negative thermal expansion (NTE) effect. Here we show that this NTE is actually X-ray-exposure dependent: Cd(CN)2 contracts not only on heating but also on irradiation by X-rays. This behaviour contrasts that observed in other beam-sensitive materials, for which X-ray exposure drives lattice expansion. We call this effect ‘negative X-ray expansion’ (NXE) and suggest its origin involves an interaction between X-rays and cyanide ‘flips’; in particular, we rule out local heating as a possible mechanism. Irradiation also affects the nature of a low-temperature phase transition. Our analysis resolves discrepancies in NTE coefficients reported previously on the basis of X-ray diffraction measurements, and we establish the ‘true’ NTE behaviour of Cd(CN)2 across the temperature range 150–750 K. The interplay between irradiation and mechanical response in Cd(CN)2 highlights the potential for exploiting X-ray exposure in the design of functional materials.

Subject Areas: Materials, Chemistry, Technique Development


Instruments: I11-High Resolution Powder Diffraction

Documents:
d0mh01989e.pdf

Discipline Tags:

Inorganic Chemistry Material Sciences Polymer Science Chemistry

Technical Tags:

Diffraction X-ray Powder Diffraction