Structural Studies on the Phase Transition of La3Ni2O6.92at about 550 K

Structural studies of La 3 Ni 2 O 6.92 with a double layered perovskite structure have been performed by the X-ray Rietveld analyses between 300 K and 650 K. The interatomic distance between Ni and the apical oxygen (on the outside of NiO 2 double layer) rapidly increases around the phase-transition temperature T B ∼550 K with decreasing temperature. Then, the energy of the (3 z 2 - r 2 ) band is considered to shift downwards with respect to that of the ( x 2 - y 2 ) band with decreasing temperature and the lower Hubbard band of the former becomes to be (almost) fully occupied at the transition temperature, which induces the Mott transition (delocalized-localized transition) of the (3 z 2 - r 2 ) electrons.