Synthesis and properties of La_1-xSr_xNiO₃ and La_1-xSr_xNiO₂

Superconductivity has been realized in films of La_1-xSr_xNiO₂. Here we report synthesis and characterization of polycrystalline samples of La_1-xSr_xNiO₃ and La_1-xSr_xNiO₂ (0 ≤ x ≤ 0.2). Magnetization and resistivity measurements reveal that La_1-xSr_xNiO₃ are paramagnetic metal and La_1-xSr_xNiO₂ exhibit an insulating behavior. Superconductivity is not detected in bulk samples of La_1-xSr_xNiO₂. The absence of superconductivity in bulk La_1-xSr_xNiO₂ may be due to the generation of hydroxide during reduction, a small amount of nickel impurity, or incomplete reduction of apical oxygen. The effect of interface in films of La_1-xSr_xNiO₂ may also play a role for superconductivity.