AbstractA new series of solid solutions of composition La21.4) were prepared. All the members of the system are of the tetragonal K2NiF4type structure. The tetragonality ratioc/ashows a progressive decrease with increasing y except for the group ofx= 1.4. The room temperature resistivity exhibits a gradual increase withy, which is interpreted by assuming that the single egelectron of Ni3+is present in localized dZ2orbital but the te electron gradually becomes itinerant because it is delocalized into dx2y2orbital leads to a strong Ni3−O2−covalent interaction with increasing the Sr content. Variation of resistance with temperature shows semiconducting properties except for the composition ofx=1.4,y<0.3 which shows a semiconductor‐to‐metal tra