Reproducibility and off-stoichiometry issues in nickelate thin films grown by pulsed laser deposition

Abstract

Rare-earth nickelates are strongly correlated oxides displaying a metal-to-insulator transition at a temperature tunable by the rare-earth ionic radius. In PrNiO 3 and NdNiO 3 , the transition is very sharp and shows an hysteretic behavior akin to a first-order transition. Both the temperature at which the transition occurs and the associated resistivity change are extremely sensitive to doping and therefore to offstoichiometry issues that may arise during thin film growth. Here we report that strong deviations in the transport properties of NdNiO 3 films can arise in films grown consecutively under nominally identical conditions by pulsed laser deposition; some samples show a well-developed transition with a resistivity change of up to five orders of magnitude while others are metallic down to low temperatures. Through a detailed analysis of in-situ X-ray photoelectron spectroscopy data, we relate this behavior to large levels of cationic off-stoichoimetry that also translate in changes in the Ni valence and bandwidth. Finally, we demonstrate that this lack of reproducibility can be remarkably alleviated by using single-phase NdNiO 3 targets.

Aspects of the synthesis of thin film superconducting infinite-layer nickelates

“…The XRD symmetric θ-2θ scan of three samples grown consecutively under fixed growth conditions (Figure 2(b)) shows that the secondary phase gradually dominates over the perovskite phase with increasing target ablation. This is in line with the previous observation of limited film reproducibility and nickel enrichment of the target over time in the PLD study of NdNiO3; 19 the favored ablation of the A-site cations from the target may increasingly promote the stabilization of the A-site-rich secondary phase over time. To avoid ambiguities arising from target history, we subsequently re-polished the target surface after each film growth.…”

Low oxygen pressure synthesis of NdNiO3-δ nanowires by electrospinning

“…From this result, the Nd/Ni ratio was calculated, and the value found was close to 1.3. This result is within range of 1.2-3.4 reported in NdNiO 3 thin films [52]. This value indicates a cationic off-stoichiometry and was related to a high Ni 2+ compared to Ni 3+ content [53].…”

“…Nonetheless, the good transport properties observed for this NNO sample suggested a low deviation of the Ni 3+ content and as a result reflects a small oxygen deficiency. The effect of this Ni valence disproportionation was also observed for NdNiO 3 thin-film samples with the Nd/Ni ratio higher than 1.2 [52].…”

“…The Ni 2+ /Ni 3+ ratio was close to 0.6, this value is in accordance with the Nd/Ni ratio. This Ni 2+ /Ni 3+ disproportionation can affect the metallic behavior and consequently decrease the T MI value [52]. Nonetheless, the good transport properties observed for this NNO sample suggested a low deviation of the Ni 3+ content and as a result reflects a small oxygen deficiency.…”

Probing photoinduced rearrangements in the NdNiO3 magnetic spiral with polarization-sensitive ultrafast resonant soft x-ray scattering

“…resistivity of the film was found to increase by almost four orders of magnitude compared to room temperature. Such a large increase through the metal-insulator transition suggests a uniform film with correct stoichiometry [38].…”