ELECTRICAL AND MAGNETIC PROPERTIES OF <font>La</font>_2−x<font>Sr</font>_x<font>NiO</font>₄: A TENTATIVE PHASE DIAGRAM

La 2−x Sr x NiO 4 shows a maximum in the c/a ratio around x=0.6 up to which composition the concentration of holes is equal to that expected theoretically. The material becomes a degenerate semiconductor above a certain temperature up to x=0.8, but is metallic at room temperature when x≥1.0. All the compositions with x≥0.05 are paramagnetic in the 15-300K range. Based on these measurements, an electronic phase diagram is tentatively proposed. It is noteworthy that the antiferromagnetic order disappears at low doping levels in both La 2−x Sr x NiO 4 and La 2−x Sr x NiO 4 , but metallicity is seen at 300K only at a much higher x value in the former system.