Dome-like pressure-temperature phase diagram of the cooperative Jahn-Teller distortion in NaNiO2
Nagle-Cocco L.A.V. Steele J.M.A. Deng S. Zhang X. Daisenberger D. Genreith-Schriever A.R. Saxena S.S. Grey C.P. Dutton S.E.
19 May 2025Institute of Physics
Journal of Physics Condensed Matter
2025#37Issue 20
NaNiO2 is a Ni3+-containing layered material consisting of alternating triangular networks of Ni and Na cations, separated by octahedrally-coordinated O anions. At ambient pressure, it features a collinear Jahn-Teller distortion below T onset JT ≈ 480 K, which disappears in a first-order transition on heating to T end JT ≈ 500 K, corresponding to the increase in symmetry from monoclinic to rhombohedral. It was previously studied by variable-pressure neutron diffraction (Nagle-Cocco et al 2022 ACS Inorg. Chem. 61 4312) and found to exhibit an increasing T onset JT with pressure up to ∼5 GPa. In this work, powdered NaNiO2 was studied via variable-pressure synchrotron x-ray diffraction up to pressures of ∼67 GPa at 294 K and 403 K. Suppression of the collinear Jahn-Teller ordering is observed via the emergence of a high-symmetry rhombohedral phase, with the onset pressure occurring at ∼18 GPa at both studied temperatures. Further, a discontinuous decrease in unit cell volume is observed on transitioning from the monoclinic to the rhombohedral phase. These results taken together suggest that in the vicinity of the transition, application of pressure causes the Jahn-Teller transition temperature, T onset JT , to decrease rapidly. We conclude that the pressure-temperature phase diagram of the cooperative Jahn-Teller distortion in NaNiO2 is dome-like.
diamond anvil cell , Jahn-Teller , phase transition , pressure
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Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge, CB3 0HE, United Kingdom
Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, United Kingdom
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British Management University Tashkent, 35 Bobur Mirza Street, Tashkent, Uzbekistan
Kazakh-British Technical University, 59 Tole Bi Street, Almaty, 050000, Kazakhstan
Cavendish Laboratory
Department of Chemistry
Diamond House
British Management University Tashkent
Kazakh-British Technical University
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