Behaviour of Jahn-Teller distorted NiO6 octahedra in NaNiO2 under pressure

Many transition metal (TM) oxides exhibit a Jahn-Teller (JT) structural distortion, and these are often susceptible to external pressure. In some materials, pressure-tuning has supressed the JT distortion entirely. XNiO2 (X=Li,Na) solid solutions, often doped with other TM ions, are important in battery research as cathode materials, and their crystal structures are heavily influenced by JT distortions in the NiO6 octahedra. NaNiO2 exhibits a cooperative JT distortion below 480 K, which elongates these octahedra and reduces the crystal symmetry from rhombohedral to monoclinic. We propose a set of diffraction measurements on NaNiO2 up to 6 GPa and 480 K, to map out the P-T phase diagram. We will be looking to see if the JT effect is quenched at high pressure, and whether this occurs by reduction in TJT towards 0 K, or by the long and short bonds in NiO6 octahedra tending towards equality.