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Thermal Polymorphism in CsCB11H12



Radovan Cerny, Matteo Brighi, Hui Wu, Wei Zhou, Mirjana Dimitrievska, Fabrizio Murgia, Valerio Gulino, Petra de Jongh, Benjamin Trump, Terrence J. Udovic


Thermal polymorphism in the alkali-metal salts incorporating the icosohedral monocarba-hydridoborate anion, CB11H12, results in intriguing dynamical properties leading to superionic conductivity for the lightest alkali-metal analogues, LiCB11H12 and NaCB11H12. As such, these two have been the focus of most recent CB11H12- related studies, with less attention paid to the heavier alkali-metal salts such as CsCB11H12. Nonetheless, it is of fundamental importance to compare the nature of the structural arrangements and interactions across the entire alkali-metal series. Thermal polymorphism in CsCB11H12 was investigated by a combination of techniques: X-ray powder diffraction; differential scanning calorimetry; Raman, infrared and neutron spectroscopies; and ab initio calculations. The unexpected temperature-dependent structural behavior of anhydrous CsCB11H12 can be potentially justified assuming the existence of two polymorphs with similar free energies at room temperature: (i) previously reported, ordered R3c stabilized upon drying and transforming to similarly packed but disordered I43d near 353 K and (ii) disordered Fm3 polymorph that initially appears from disordered I43d near 513 K along with another disordered high-temperature P63mc polymorph. Quasielastic neutron scattering results indicate that the CB11H12- anions in the disordered phase at 560 K are undergoing isotropic rotational diffusion, with a jump correlation frequency of 1.19(9)×1011 s-1 in line with frequencies for the lighter-metal analogues.


anion dynamics, carba-hydridoborate, crystal structure, CsCB11H12, neutron vibrational spectroscopy, polymorphism, quasielastic neutron scattering, X-ray powder diffraction


Cerny, R. , Brighi, M. , Wu, H. , Zhou, W. , Dimitrievska, M. , Murgia, F. , Gulino, V. , de Jongh, P. , Trump, B. and Udovic, T. (2023), Thermal Polymorphism in CsCB11H12, Molecules, [online], (Accessed June 23, 2024)


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Created March 1, 2023, Updated January 23, 2024