亚稳相钙钛矿稀土镍酸盐薄膜材料的可控生长与电子相变性质

Controllable growth and electronic phase transitions for metastable perovskite rare-earth nickelate films

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摘要稀土镍酸盐(ReNiO_(3),Re为镧系稀土元素)由特征温度场、氢化、临界电场及应力场等多物理参量引发的多重电子相变及物性突变引起了凝聚态物理和材料科学领域的广泛关注,在突变式敏感电阻元器件、人工智能、能量转换及弱电场传感等领域展现出可观的应用前景.然而,ReNiO_(3)材料本征的热力学亚稳性仍制约其在关联电子器件中的实际应用.本文利用激光分子束外延法制备出原子级平整的亚稳态ReNiO_(3)(Re=Nd,Sm及Nd_(1-x)Sm_(x))薄膜材料,阐明高氧压原位退火在稳定其Ni^(3+)扭曲钙钛矿结构中的关键作用,结合同步辐射和X射线光电子能谱等先进表征手段厘清ReNiO_(3)薄膜材料的化学环境及电子结构,并揭示出其各向异性的电子相变功能特性.本文为制备原子级平整的亚稳态钙钛矿稀土镍酸盐薄膜材料提供了方向,并引入全新的功能调控自由度——晶体学各向异性,为进一步探索稀土镍酸盐材料体系中的新型电子相和功能特性奠定基础. The multiple electronic phase transition achieved in the metastable perovskite(ReNiO_(3),where Re denotes a lanthanide rare-earth element) by using critical temperature,hydrogenation,electrical field and inter facial strain has attracted considerable attention in condensed matter physics and materials science,making it promising applications in the critical temperature thermistor,artificial intelligence,energy conversion and weak electric field sensing.Nevertheless,the above abundant applications are still bottlenecked by the intrinsically thermodynamic metastability related to ReNiO_(3).Herein,we synthesize the atomic-level flat ReNiO_(3) film material with thermodynamic metastability using laser molecular beam epitaxy(LMBE) that exhibits excellent thermally-driven electronic phase transitions.Notably,the interfacial heterogeneous nucleation of ReNiO_(3) film can be triggered by the template effect of(001)-oriented LaAlO_(3) substrates,owing to the similar lattice constants between LaAlO_(3) substrate and ReNiO_(3) film.In addition,we elucidate the key role of in situ annealing under oxygen-enriched atmosphere in stabilizing the distorted perovskite structure related to ReNiO_(3).Apart from the depositing process related to LMBE,the ReNiO_(3) with heavy rare-earth composition exhibits a more distorted NiO_(6) octahedron and a higher Gibbs free energy that is rather difficult to synthesize by using physical vacuum deposition.As a representative case,the in situ annealing-assisted LMBE process cannot be utilized to deposit the SmNiO_(3) film,in which the impurity peaks related to Re_2O_(3) and NiO are observed in its XRD spectra.With the assistance of X-ray photoelectron spectraoscopy and near-edge X-ray absorption fine structure,the valence state of nickel for ReNiO_(3) is found to be+3,and the t_(2g)^(6)e_(g)^(1) configuration is observed.Considering the highly tunable electronic orbital configuration of ReNiO_(3) related to the NiO_(6) octahedron,cooccupying the A-site of perovskite structure with Nd and Sm elements regulates the transition temperature(T_(MIT)) for ReNiO_(3) within a broad temperature range.Furthermore,we demonstrate the anisotropy in the electronic phase transitions for Nd_(1-x)Sm_(x)NiO_(3),in which case the T_(MIT) achieved in the Nd_(1-x)Sm_(x)NiO_(3)/LaAlO_(3)(111) heterostructure exceeds the one deposited on the(001)-oriented LaAlO_(3) substrate.The presently observed anisotropy in the electrical transportation for Nd_(1-x)Sm_(x)NiO_(3) film material is related to the anisotropic in-plane NiO_(6) octahedron configuration triggered by differently oriented LaAlO_(3) substrates.The present work is expected to introduce a new degree of freedom to regulate the electronic phase transition,explore new electronic phase in ReNiO_(3) material system,and pave the way for growing atomic-level flat ReNiO_(3) film materials with expected electronic phase transitions.

作者周轩弛焦勇杰 Zhou Xuan-Chi;Jiao Yong-Jie(Key Laboratory of Magnetic Molecules and Magnetic Information Materials of Ministry of Education,School of Chemistry and Materials Science,Shanxi Normal University,Taiyuan 030031,China;Collaborative Innovation Center for Shanxi Advanced Permanent Magnetic Materials and Technology,Research Institute of Materials Science,Shanxi Normal University,Taiyuan 030031,China)

机构地区山西师范大学化学与材料科学学院山西师范大学材料科学研究院