Pressure Tuning the Jahn-Teller Transition Temperature in NaNiO2.
American Chemical Society (ACS)
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Nagle-Cocco, L., Bull, C. L., Ridley, C. J., & Dutton, S. (2022). Pressure Tuning the Jahn-Teller Transition Temperature in NaNiO2.. Inorg Chem https://doi.org/10.1021/acs.inorgchem.1c03345
NaNiO2 is a layered material consisting of alternating layers of NaO6 and Jahn-Teller-active NiO6 edge-sharing octahedra. At ambient pressure, it undergoes a broad phase transition from a monoclinic to rhombohedral structure between 465 and 495 K, associated with the loss of long-range orbital ordering. In this work, we present the results of a neutron powder diffraction study on powdered NaNiO2 as a function of pressure and temperature from ambient pressure to ∼5 GPa between 290 and 490 K. The 290 and 460 K isothermal compressions remained in the monoclinic phase up to the maximum pressures studied, whereas the 490 K isotherm was mixed-phase throughout. The unit-cell volume was fitted to a second-order Birch-Murnaghan equation of state, where B = 119.6(5) GPa at 290 K. We observe at 490 K that the fraction of the Jahn-Teller-distorted phase increases with pressure, from 67.8(6)% at 0.71(2) GPa to 80.2(9)% at 4.20(6) GPa. Using this observation, in conjunction with neutron diffraction measurements at 490 K on removing pressure from 5.46(9) to 0.342(13) GPa, we show that the Jahn-Teller transition temperature increases with pressure. Our results are used to present a structural pressure-temperature phase diagram for NaNiO2. To the best of our knowledge, this is the first diffraction study of the effect of pressure on the Jahn-Teller transition temperature in materials with edge-sharing Jahn-Teller-distorted octahedra and the first variable-pressure study focusing on the Jahn-Teller distortion in a nickelate.
Is supplemented by: https://doi.org/10.17863/CAM.81605
This work was supported by the Faraday Institution grant number FIRG017. LNC acknowledges a scholarship EP/R513180/1 to pursue doctoral research from the UK Engineering and Physical Sciences Research Council (EPSRC). Experiments at the ISIS Neutron and Muon Source were supported by a beamtime allocation RB2000219 from the Science and Technology Facilities Council of the United Kingdom.
Engineering and Physical Sciences Research Council (2275821)
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External DOI: https://doi.org/10.1021/acs.inorgchem.1c03345
This record's URL: https://www.repository.cam.ac.uk/handle/1810/334215
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