Structure and phase transitions in layered nickelates

A La3Ni2O7 lattice is shown to be built of interlacing double-layer 2(LaO x NiO2) blocks and single-layer LaO blocks LaO layers situated between negatively charged NiO2 and positively charged LaO are split into layers of cations and anions. A similar layer splitting takes place in other layered nickelates and cuprates. It suggests the prevaling significance of electrostatic interaction between neighbor layers. An ortho-tetra phase transition is found at 870 K which is due to oxygen octahedron rotation round a nickel atom. The temperature of the phase transition in layered nickelates rises with the increase of the number of layers in the perovskite block