摘要
通过高通量第一性原理模拟，该研究系统比较了delafossite（D1）、有序岩盐变体（D2）及无限层（IL）氧化物在ABO2化学计量下的热力学稳定性，并构建了涵盖2346种元素组合的相图。结果表明，对于镍酸盐、钯酸盐和铂酸盐，delafossite结构的稳定性与无限层相相当甚至更优，且这两种相与钙钛矿相之间存在竞争关系。电子结构分析显示，delafossite化合物具有反转的阳离子顺序，费米面以dz2轨道贡献为主，显著区别于无限层相的dx2-y2特征。在所有候选体系中，La-Ni组合是稳定无限层结构的热力学最优选择。此外，通过Ca、Sr、Ba进行空穴掺杂可系统提高三种过渡金属家族中无限层相的相对稳定性。这些结果揭示了合成无衬底体相无限层氧化物的根本挑战，并为实验探索新型超导化合物提供了指导。
材料
方法
- High-throughput first-principles density functional theory (DFT) simulations with on-site Coulomb repulsion (DFT+U)
- Convex hull analysis
关键词
- delafossite
- competing phase
- thermodynamic stability
- reversed cation order
- dz2 dominated fermi surface
- hole doping stabilization
亮点
- The delafossite structure is found to be a strong competitor to the infinite-layer phase, with reversed cation order.
- BaAgO2 is identified as a stable isoelectronic analog to infinite-layer cuprates with similar electronic structure.
- The results reveal fundamental challenges in realizing bulk substrate-free infinite-layer oxides.
结论
- The delafossite structure rivals the infinite-layer phase in thermodynamic stability for nickelates, and even more for palladates and platinates.
- Among all candidates, the La-Ni combination stands out as a thermodynamic optimum for stabilizing the infinite-layer motif.
- Hole doping via Ca, Sr, and Ba systematically enhances the stability of the infinite-layer phase in all three transition-metal families.
- The delafossite compounds exhibit a strongly dz2-dominated Fermi surface, in contrast to the dx2-y2 character in infinite-layer phases.
主要论断
- Delafossite structure (D1) is a strong competitor to the infinite-layer phase for nickelates, palladates, and platinates, often with lower formation energy.
- 证据: From abstract: 'delafossite structure rivals the infinite-layer phase in thermodynamic stability for the nickelates, and even more for the recently suggested palladate and platinate analogs.',From Section III.A: 'Table I even reveals a minor energetic preference of 0.02-0.09 eV for the D1 structure' for nickelates; for palladates/platinates D1 is ≈0.3-0.8 eV more stable.
- The La-Ni combination is the thermodynamic optimum for stabilizing the infinite-layer phase among rare-earth/transition-metal pairings.
- 证据: From abstract: 'Among all candidates, the La-Ni combination stands out as a thermodynamic optimum for stabilizing the infinite-layer motif.',From Section III.B: 'Our statistical analysis highlights LaNi as the most favorable rare-earth/transition-metal pairing for stabilizing the IL phase.'
- Hole doping via Ca, Sr, and Ba systematically enhances the relative stability of the infinite-layer phase and lowers the reduction energy.
- 证据: From abstract: 'hole doping via Ca, Sr, and Ba systematically enhances the stability of the infinite-layer phase in all three transition-metal families.',From Section III.A: 'Ca-, Sr-, and Ba-based compounds consistently favor the IL phase as their ground state' and 'such substitution tends to lower the reduction energy relative to the parent P phase.'
- In delafossite compounds, the Fermi surface is dominated by d_z2 states due to reversed cation order, whereas infinite-layer phases have dx2-y2 character.
- 证据: From abstract: 'delafossite compounds… exhibit a strongly d_z2-dominated Fermi surface, in stark contrast to the dx2-y2 character observed in the infinite-layer phases.',From Section III.C: 'In the D1 structure, exclusively the d_z2 states contribute to the Fermi surface' vs. 'the dx2-y2-derived bands exhibit the highest dispersion' in IL.
- BaAgO2 is identified as a stable isoelectronic infinite-layer compound with electronic structure similar to CaCuO2, making it a candidate for superconductivity.
- 证据: From Section III.A: 'BaAgO2 is isoelectronic to the IL cuprates and presents a highly similar band structure' and from Appendix B: 'Both Fermi surfaces are predominantly of dx2-y2 character and exhibit a highly similar shape.'
研究流程
- High-throughput DFT simulations — Constructed a database of 7,038 unique delafossite and ordered rock-salt compounds.
- 材料: 2,346 elemental combinations at A and B sites; D1, D2, IL, P geometries
- 方法: DFT+U with projector-augmented wave (PAW) formalism; VASP code; GGA-PBE exchange-correlation functional
- 观察: Ground-state energies for 16,422 individual structure optimizations; Formation energies (Ef) for ABO2 and ABO3 compounds
- Phase diagram construction — Delafossite structure rivals infinite-layer phase in thermodynamic stability for nickelates, palladates, and platinates.
- 材料: Formation energies from DFT simulations
- 方法: Comparison of Ef for D1, D2, IL, and P phases; Vector-based color mapping to visualize stability sectors
- 观察: Relative stability sectors: D1 (65%), D2 (20%), IL (15%); Only 9% of IL compounds have negative reduction energy
- Electronic structure analysis — Delafossite compounds exhibit reversed cation order and strongly d_z2-dominated Fermi surface, contrasting with infinite-layer dx2-y2 character.
- 材料: Neodymium-based nickelates, palladates, platinates (NdNiO2, NdPdO2, NdPtO2); Also CaCuO2 and BaAgO2
- 方法: Orbital-resolved band structure calculations; Fermi surface visualization
- 观察: In D1: Fermi surface dominated by d_z2 states from transition metal at A-site; In IL: Fermi surface dominated by dx2-y2 states from transition metal at B-site