Synthesis and physical properties of perovskite Sm1−x Sr x NiO3 (x = 0, 0.2) and infinite-layer Sm0.8Sr0.2NiO2 nickelates

Abstract

Recently, superconductivity at about 9–15 K was discovered in Nd1−x Sr x NiO2 (Nd-112, x ≈ 0.125–0.25) infinite-layer thin films, which has stimulated enormous interests in related rare-earth nickelates. Usually, the first step to synthesize this 112 phase is to fabricate the RNiO3 (R-113, R: rare-earth element) phase, however, it was reported that the 113 phase is very difficult to be synthesized successfully due to the formation of unusual Ni3+ oxidation state. And the difficulty of preparation is enhanced as the ionic radius of rare-earth element decreases. In this work, we report the synthesis and investigation on multiple physical properties of polycrystalline perovskites Sm1−x Sr x NiO3 (x = 0, 0.2) in which the ionic radius of Sm3+ is smaller than that of Pr3+ and Nd3+ in related superconducting thin films. The structural and compositional analyses conducted by x-ray diffraction and energy dispersive x-ray spectrum reveal that the samples mainly contain the perovskite phase of Sm1−x Sr x NiO3 with small amount of NiO impurities. Magnetization and resistivity measurements indicate that the parent phase SmNiO3 undergoes a paramagnetic–antiferromagnetic transition at about 224 K on a global insulating background. In contrast, the Sr-doped sample Sm0.8Sr0.2NiO3 shows a metallic behavior from 300 K down to about 12 K, while below 12 K the resistivity exhibits a slight logarithmic increase. Meanwhile, from the magnetization curves, we can see that a possible spin-glass state occurs below 12 K in Sm0.8Sr0.2NiO3. Using a soft chemical reduction method, we also obtain the infinite-layer phase Sm0.8Sr0.2NiO2 with square NiO2 planes. The compound shows an insulating behavior which can be described by the three-dimensional variable-range-hopping model. And superconductivity is still absent in the polycrystalline Sm0.8Sr0.2NiO2.