Displacive Jahn–Teller transition in NaNiO2 by Nagle-Cocco, LAV, Genreith-Schriever, AR, Steele, JMA, Tacconis, C, Bocarsly, JD, Mathon, O, Neuefeind, JC, Liu, J, O’Keefe, CA, Goodwin, AL, Grey, CP, Evans, JSO, Dutton, S