INVESTIGATIONS ON THE STRUCTURAL, ELECTRICAL, AND MAGNETIC-PROPERTIES OF ND2-XSRXNIO4+DELTA

Solid-solutions of the type Nd2-xSrxNiO4+δ (0 ≤ x ≤ 1) were prepared by codecomposition of the metal nitrates and were characterized by means of powder X-ray diffraction, TGA, electrical resistivity, and magnetic susceptibility measurements. Nd2NiO4+δ possesses orthorhombic symmetry at ambient temperatures and exhibits a phase transition to pseudo-tetragonal symmetry upon doping with Sr2+ (x ≈ 0.2). The tetragonality ratio c at measured as a function of x shows an anomalous increase at x ≈ 0.2 and a maximum near x = 0.6. Considerable deviation from oxygen stoichiometries was observed in the orthorhombically distorted members, while for the samples with tetragonal geometry the oxygen contents were near the ideal value. All the samples, except NdSrNiO4, were semiconducting from room temperature down to 10 K. NdSrNiO4 showed a metal-semiconductor transition at ∼ 190 K. The magnetic susceptibility shows Curie-Weiss behavior with an onset of long range antiferromagnetic ordering (TN = 17 K) in some of the intermediate members of the solid-solution series. The effect of Sr2+ substitution on the structural and electronic properties of Nd2-xSrxNiO4+δ are discussed in terms of the mixed valence character of Ni2+ Ni3+, distortions in the local coordination of NiO octahedra, and correlation effects of dx bands in the NiO basal plane. © 1990.