Structural and magnetic properties of (Ro_0.5A _0.5)NIO₃ perovskites (R = GD, YB and A = CE, TH)

Four perovskite compounds with nominal compositions of (Gd _0.5Th_0.5)NiO₃, (Gd_0.5Ce _0.5)NiO₃, (Yb_0.5Th_0.5)NiO ₃ and (Yb_0.5Ce_0.5)NiO₃ were prepared by a polymeric citrate precursor method. They were either slow-cooled in the furnace or quenched to room temperature. All of them have monoclinic symmetry. Quenched samples have a slightly bigger unit cell volume and longer Ni-O bond length, and a smaller grain size than that of the furnace-cooled compounds. All samples are paramagnetic insulators in the range of 2 K to 300 K. The Th containing compounds have larger tolerance factor and Ni(1)-O(1)-Ni(2) bond angle than that of the Ce containing compounds. No mixed valence of Ce, Th and Ni is observed in these samples.