Transport and Magnetic Properties of La3Ni2O7- δand La4Ni3O10- δ

Metal-insulator transitions of La 3 Ni 2 O 7-δ and La 4 Ni 3 O 10-δ with layered structure have been studied. Transport and magnetic measurements up to 1000 K have revealed an existence of the sharp transition in both systems at 550 K from a metallic but less conducting state with localized spins at Ni sites to the Pauli paramagnetic and more conducting one with increasing temperature. The transition is explained by a model that the Mott transition takes place in the "half-filled" band of 3 d 3 z 2 - r 2 orbitals at the temperature, and that below the temperature, the conduction of the electrons in the 3 d x 2 - y 2 band is disturbed by the Hund coupling with the localized electrons in the 3 d 3 z 2 - r 2 band.