Accessibility navigation

Phonon dynamics in the layered negative thermal expansion compounds CuxNi2-x(CN)4

d'Ambrumenil, S., Zbiri, M., Chippindale, A. and Hibble, S. (2019) Phonon dynamics in the layered negative thermal expansion compounds CuxNi2-x(CN)4. Physical Review B, 100 (9). 094312. ISSN 1098-0121

Text - Accepted Version
· Please see our End User Agreement before downloading.


It is advisable to refer to the publisher's version if you intend to cite from this work. See Guidance on citing.

To link to this item DOI: 10.1103/PhysRevB.100.094312


This study explores the relationship between phonon dynamics and negative thermal expansion (NTE) in CuxNi2-x¬(CN)4. The partial replacement of nickel (II) by copper (II) in Ni(CN)2 leads to a line phase, CuNi(CN)4 (x = 1), and a solid solution, CuxNi2-x¬(CN)4 (0 ≤ x ≤ 0.5). CuNi(CN)4 adopts a layered structure related to that of Ni(CN)2¬ (x = 0), and interestingly exhibits 2D NTE which is ~ 1.5 times larger. Inelastic neutron scattering (INS) measurements combined with first principles lattice dynamical calculations provide insights into the effect of Cu2+ on the underlying mechanisms behind the anomalous thermal behavior in all the CuxNi2-x¬(CN)4 compounds. The solid solutions are presently reported to also show 2D NTE. The INS results highlight that as the Cu2+ content increases in CuxNi2-x(CN)4, large shifts to lower energies are observed in modes consisting of localized in- and out-of-plane librational motions of the CN ligand, which contribute to the NTE in CuNi(CN)4. Mode Grüneisen parameters calculated for CuNi(CN)4 show that acoustic and low-energy optic modes contribute the most to the NTE, as previously shown in Ni(CN)2. However, mode eigenvectors reveal a large deformation of the [CuN4] units compared to the [NiC4] units, resulting in phonon modes not found in Ni(CN)2, whose NTE-driving phonons consist predominately of rigid-unit modes. The deformations in CuNi(CN)4 arise because the d9 square-planar center is easier to deform than the d8 one, resulting in a greater range of out-of-plane motions for the adjoining ligands.

Item Type:Article
Divisions:Interdisciplinary centres and themes > Chemical Analysis Facility (CAF)
Life Sciences > School of Chemistry, Food and Pharmacy > Department of Chemistry
ID Code:86271
Publisher:American Physical Society


Downloads per month over past year

University Staff: Request a correction | Centaur Editors: Update this record

Page navigation