Protonation-Induced Colossal Chemical Expansion and Property Tuning in NdNiO₃ Revealed by Proton Concentration Gradient Thin Films

Abstract

Protonation can be used to tune diverse physical and chemical properties of functional oxides. Although protonation of nickelate perovskites has been reported, details on the crystal structure of the protonated phase and a quantitative understanding of the effect of protons on physical properties are still lacking. Therefore, in this work, we select NdNiO 3 (NNO) as a model system to understand the protonation process from pristine NNO to protonated H x NdNiO 3 (H-NNO). We used a reliable electrochemical method with well-defined reference electrode to trigger the protonation-induced phase transition. We found that the protonated H-NNO phase showed a colossal ∼13% lattice expansion caused by a large tilt of NiO 6 octahedra and displacement of Nd cations. Importantly, we further designed a novel device configuration to induce a gradient of proton concentration into a single NNO thin film to establish a quantitative correlation between the proton concentration and the lattice constant and transport property of H-NNO.

Protonation-Induced Colossal Lattice Expansion in La2/3Sr1/3MnO3

“…When subjected to a positive bias voltage, protons intercalate into the LSMO lattice while concurrently absorbing electrons released during oxidation at the counter electrode, in order to maintain electrical neutrality. , Figure d illustrates a schematic representation of the proton diffusion process within the LSMO film, encompassing four key steps: (1) rotational diffusion of protons, (2) migration to adjacent oxygen sites, (3) elongation, and (4) tilting of the Mn–O bonds. − In the LSMO lattice, the intercalated protons primarily formed bonds with oxygen atoms, resembling the bonding pattern observed in other oxides . Thus, proton diffusion promotes the tilting of MnO 6 octahedra, hence promoting colossal lattice expansion in the out-of-plane direction . This significant lattice expansion observed during hydrogenation holds promising implications from an application standpoint, such as in hydrogen storage …”

“…The large lattice expansion induced by hydrogenation coincides with the changes in the oxidation state and oxygen bonding, resulting in stretching and tilting in the MnO 6 octahedra. 39 To investigate valence changes, we conducted ex situ X-ray photoemission spectroscopy of Mn ions. Proton diffusion has a pronounced impact on the manganese valence states in the perovskite-based LSMO.…”

“…40 Thus, proton diffusion promotes the tilting of MnO 6 octahedra, hence promoting colossal lattice expansion in the out-of-plane direction. 39 This significant lattice expansion observed during hydrogenation holds promising implications from an application standpoint, such as in hydrogen storage. 20 Figure 1c presents the out-of-plane lattice parameter "c" for pristine, hydrogenated, and annealed LSMO films.…”

Deeper mechanistic insights into epitaxial nickelate electrocatalysts for the oxygen evolution reaction

“…There has been mounting evidence that shows the surface and the ''bulk'' (at least several nanometers from the interface into the electrocatalysts) can participate in the electrochemical reaction, and often determines the kinetics and performance of these electrocatalysts. 15,[23][24][25][26][27] Therefore, a holistic picture considering the solid/liquid interfaces, as well as the constituent ions and ionic defects of TMOs, becomes important for understanding the reaction mechanism and guiding the predictive design of nickelate OER electrocatalysts. Due to the participation of electrocatalyst ''bulk'' during the electrochemical reactions, a wide range of dynamic mechanisms and phenomena have been observed.…”

Strong spin-lattice entanglement in cobaltites

“…利用脉冲激光沉积技术， Li 等制备了一系列不同厚度和周期的 LaCoO 3 /SrCuO 2 超晶格 [72] 之外，氧八面体倾转同样是界面调控的一个重要方式 [73][74][75] 。通过改变调控层的氧 八面体倾转角，可以调控共顶点连接的功能层的八面体倾转方式，进而改变过渡 金属离子与氧离子的键角，调控电子在不同轨道间占据的几率，影响整个异质结 构的物理特性。有的时候，这种晶格调控的方式比化学掺杂甚至衬底应力对物性 调控更有效果。Liao 等 [76] 利用 NdGaO 3 衬底引入的八面体倾转有效地调控了锰氧 化物薄膜的磁和电输运的各向异性，使其磁易轴的方向发生出人意料的旋转，表 现出很强的各向异性磁阻。更有趣的是，在衬底和薄膜之间插入单原胞层 SrTiO 3 后，这种八面体倾转就完全消失了，说明这种界面效应极易受到外延薄膜对称性 的影响。与此同时，Kan 等 [77] 在 GdScO 子替换的研究却非常少见。通过在离子液体两端加不同极性的电压，研究人员在 镍氧化物 [94] 和 SrCoO x 体系 [95] 中实现了氧离子和氢离子的可控掺杂，进而实现多 种物态的高效调控。最近，Li 等 [96] 甚至能够利用扫描探针在微纳尺度下进行可 控离子掺杂并实现金属-绝缘体相变。此外，原位进行 F - [97] 或者 N 3-[98] 离子掺杂 的技术也已经日趋成熟。通过阴离子工程，不仅可以改变钴氧化物薄膜中钴离子 的价态以及随之变化的自旋态， 而且可以调控该材料的晶格畸变甚至产生新的物 相。以上的研究方向亟待研究人员进一步深入探索，对于发现钴氧化物薄膜的新 奇物性以及物态调控都具有十分重要的意义。…”