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The Effect of Ultraviolet Radiation on the Chemical Bath Deposition of Bisthiourea Cadmium Chloride Crystals and the Subsequent CdS Obtention
Published on: August 30, 2018
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Negative X-ray expansion in cadmium cyanide
Chloe S Coates1, Claire A Murray, Hanna L B Boström
1Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, UK. andrew.goodwin@chem.ox.ac.uk.
Materials Horizons
|November 30, 2021
Summary
Cadmium cyanide exhibits negative thermal expansion (NTE) that is dependent on X-ray exposure. This material contracts under X-ray irradiation, a phenomenon termed negative X-ray expansion (NXE).
Area of Science:
- Materials Science
- Solid-State Chemistry
- Crystallography
Background:
- Cadmium cyanide (Cd(CN)2) is a flexible coordination polymer known for its strong negative thermal expansion (NTE).
- Previous studies on Cd(CN)2 using X-ray diffraction (XRD) have reported varying NTE coefficients, suggesting potential complexities.
- Understanding the factors influencing the structural behavior of coordination polymers is crucial for materials design.
Purpose of the Study:
- To investigate the influence of X-ray exposure on the structural properties of cadmium cyanide.
- To elucidate the mechanism behind the observed negative thermal expansion (NTE) and introduce the concept of negative X-ray expansion (NXE).
- To resolve discrepancies in previously reported NTE coefficients and establish the true NTE behavior of Cd(CN)2.
Main Methods:
- X-ray diffraction (XRD) measurements at various temperatures and under X-ray irradiation.
- Analysis of structural changes and lattice parameters in response to thermal and X-ray stimuli.
- Computational modeling to explore potential mechanisms, ruling out local heating effects.
Main Results:
- Cadmium cyanide demonstrates negative X-ray expansion (NXE), contracting upon X-ray irradiation, unlike other beam-sensitive materials.
- The NTE of Cd(CN)2 is confirmed to be X-ray-exposure dependent, with NXE originating from interactions with cyanide 'flips'.
- X-ray irradiation influences the low-temperature phase transition of Cd(CN)2, and the true NTE behavior was established between 150-750 K.
Conclusions:
- The NTE of cadmium cyanide is significantly influenced by X-ray exposure, leading to the phenomenon of NXE.
- Discrepancies in prior NTE studies are resolved by accounting for X-ray-induced structural changes.
- The interplay of irradiation and mechanical response in Cd(CN)2 suggests potential applications in designing novel functional materials.
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