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Pressure Tuning the Jahn-Teller Transition Temperature in NaNiO2
Liam A V Nagle-Cocco1, Craig L Bull2,3, Christopher J Ridley2
1Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
Sodium nickelate (NaNiO2) shows a pressure-dependent Jahn-Teller transition. Increasing pressure raises the transition temperature, impacting its structural phases and orbital ordering.
Area of Science:
- Materials Science
- Solid-State Physics
- Crystallography
Background:
- Sodium nickelate (NaNiO2) is a layered material featuring Jahn-Teller-active NiO6 octahedra.
- At ambient pressure, NaNiO2 exhibits a phase transition linked to orbital ordering loss between 465-495 K.
Purpose of the Study:
- Investigate the structural response of NaNiO2 under varying pressure and temperature.
- Determine the effect of pressure on the Jahn-Teller transition temperature in NaNiO2.
Main Methods:
- Neutron powder diffraction was employed to study NaNiO2 from ambient pressure to ~5 GPa and 290-490 K.
- Equation of state analysis using the Birch-Murnaghan model was performed to determine bulk modulus.
Main Results:
- The monoclinic phase persisted up to ~5 GPa at 290 K and 460 K.
- At 490 K, the Jahn-Teller-distorted phase fraction increased with pressure, indicating a pressure-induced transition.
- The Jahn-Teller transition temperature was found to increase with applied pressure.
Conclusions:
- A structural pressure-temperature phase diagram for NaNiO2 was established.
- This study provides the first diffraction data on pressure effects on Jahn-Teller transitions in edge-sharing octahedra materials.
- It is the first variable-pressure study on Jahn-Teller distortion in a nickelate.
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