Structural disorder and antiferromagnetism in LaNi1–xPtxO3

Abstract

We report on the B-site substitution of Pt for Ni in the system LaNi1–xPtxO3. The system can only be synthesized between x ​≤ ​0.50, with LaNiO3 (x ​= ​0.00) and the stoichiometric double perovskite La2NiPtO6 (x ​= ​0.50) as the end members. Higher Pt-contents (x ​> ​0.50) are unachievable due to the preference of Pt to being in oxidation state ​+ ​IV in octahedral coordination. Upon introducing Pt into LaNiO3, a phase transformation from rhombohedral (R-3c) to monoclinic (P21/n) symmetry is observed for 0.075 ​≤ ​x ​≤ ​0.125, where all monoclinic samples are B-site ordered, and Pt show a strong preference for the Pt-site (2c-site) for all compositions (x ​≥ ​0.20). Powder X-ray diffraction analysis reveal disorder of the Pt-distribution in several of the non-equimolar samples (0.20 ​≤ ​x ​≤ ​0.40), which point toward cluster formation with domains of high and low Pt-content within each sample. La2NiPtO6 further show an antiferromagnetic transition at ∼ 40 ​K. A similar transition is observed for all monoclinic samples (x ​≥ ​0.20), however, the transition is less pronounced for lower x. This is explained in terms of the structural disorder, i.e. by the coexistence of antiferromagnetic domains with long range order and paramagnetic domains dominated by short range antiferromagnetic interactions.