Synthesis and physical properties of perovskite Sm_1−x Sr _x NiO₃ (x = 0, 0.2) and infinite-layer Sm_0.8Sr_0.2NiO₂ 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.

Infinite-Layer Nickelate Superconductors: A Current Experimental Perspective of the Crystal and Electronic Structures

“…Superconductivity is missing in the bulk infinite-layer nickelate [23,[44][45][46]. The puzzling limitation in the thickness of the infinite-layer thin film further warrants the importance of investigating the thickness dependency of the physical observables and electronic structure of the infinite-layer nickelate.…”

Limits to the strain engineering of layered square-planar nickelate thin films

“…Nevertheless, La 1−x Ca x NiO 2 and Pr 4 Ni 3 O 8 35 single crystals are metallic but not yet superconducting to date. In contrast, most reduced infinite-layer [32][33][34]77 and layered nickelate powders [19][20][21][22][78][79][80] are insulating-metallic (Pr, Nd) 4 Ni 3 O 8 pellets were, however, achieved with reductions using a sulfur getter to promote the removal of apical oxygens 81,82 . Thus metallicity in square-planar, or T 0 , nickelates may be exquisitely sensitive to the oxygen content like in T 0 cuprates 83 .…”

Experimental progress on the emergent infinite-layer Ni-based superconductors

“…Up to now, more bulk infinite-layer nickelate compounds with other rare earth elements or other dopants have been successfully synthesized. For example, in 2020, He et al [126] demonstrated the successful preparation of bulk polycrystalline infinite-layer Sm0.8Sr0.2NiO2. In 2021, Puphal et al [127] reported the synthesis of high-quality single-crystal infinite-layer La1-xCaxNiO2+.…”