Phonon dynamics in the layered negative thermal expansion compounds CuxNi2−x(CN)4
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...
| Main Authors: | , , , |
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| Format: | Journal article |
| Language: | English |
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American Physical Society
2019
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| _version_ | 1826274684785655808 |
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| author | D’Ambrumenil, S Zbiri, M Chippindale, A Hibble, S |
| author_facet | D’Ambrumenil, S Zbiri, M Chippindale, A Hibble, S |
| author_sort | D’Ambrumenil, S |
| collection | OXFORD |
| description | 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 two-dimensional (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 |
| first_indexed | 2024-03-06T22:47:12Z |
| format | Journal article |
| id | oxford-uuid:5d94f554-8831-4e55-b84a-3ebde717b705 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T22:47:12Z |
| publishDate | 2019 |
| publisher | American Physical Society |
| record_format | dspace |
| spelling | oxford-uuid:5d94f554-8831-4e55-b84a-3ebde717b7052022-03-26T17:35:22ZPhonon dynamics in the layered negative thermal expansion compounds CuxNi2−x(CN)4Journal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:5d94f554-8831-4e55-b84a-3ebde717b705EnglishSymplectic Elements at OxfordAmerican Physical Society2019D’Ambrumenil, SZbiri, MChippindale, AHibble, SThis 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 two-dimensional (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 |
| spellingShingle | D’Ambrumenil, S Zbiri, M Chippindale, A Hibble, S Phonon dynamics in the layered negative thermal expansion compounds CuxNi2−x(CN)4 |
| title | Phonon dynamics in the layered negative thermal expansion compounds CuxNi2−x(CN)4 |
| title_full | Phonon dynamics in the layered negative thermal expansion compounds CuxNi2−x(CN)4 |
| title_fullStr | Phonon dynamics in the layered negative thermal expansion compounds CuxNi2−x(CN)4 |
| title_full_unstemmed | Phonon dynamics in the layered negative thermal expansion compounds CuxNi2−x(CN)4 |
| title_short | Phonon dynamics in the layered negative thermal expansion compounds CuxNi2−x(CN)4 |
| title_sort | phonon dynamics in the layered negative thermal expansion compounds cuxni2 x cn 4 |
| work_keys_str_mv | AT dambrumenils phonondynamicsinthelayerednegativethermalexpansioncompoundscuxni2xcn4 AT zbirim phonondynamicsinthelayerednegativethermalexpansioncompoundscuxni2xcn4 AT chippindalea phonondynamicsinthelayerednegativethermalexpansioncompoundscuxni2xcn4 AT hibbles phonondynamicsinthelayerednegativethermalexpansioncompoundscuxni2xcn4 |