Multicomponent equiatomic high entropy oxides - synthesis and magneto-electronics properties

多组分高熵氧化物（HEOs）是一组由5个或5个以上的阳离子以几乎相等的原子比例组成的单相氧化物固溶体。虽然HEO领域的发展还不到五年，但不同类别的HEO的一些有趣的结构和功能特征已经被报道，其中包括我们在初始资助期内进行的一些开创性的研究。初步供资期间的更具体成就如下：(a)发现了稀土过渡金属钙钛矿- heos （P-HEOs）和阴离子无序高熵氧氟化物（HEOFs）， (b)证明了岩盐- heos和HEOFs作为锂离子电池阳极和阴极的优越电化学性能，(d)阐明了荧光- heos的可逆控制能带结构，最后，(e)观察到由P-HEOs的极端化学无序引起的奇异磁现象，如交换偏置，磁晶各向异性大，室温下矫顽力场大等。这些结果是相当基础但不同的调查的结果，旨在探索heo领域是否值得研究。实际上，这项开创性的研究已经强调了基于多组分高熵的设计方法可以提供的前所未有的物理化学现象。这项研究计划的主要目的是将一类新的材料引入磁电子学领域，这些材料通过利用高熵方法提供的阳离子和阴离子位置的化学无序来增强或迄今未知的功能。基于已有的结果，我们选择稀土过渡金属p - heo族作为本次探索的主要heo类，这些结果表明它们在化学无序性、突出的结构畸变和异常自旋电子态稳定之间具有很强的内在联系。当然，P-HEOs作为一种材料类别也是一个最佳选择，因为母矿钙钛矿具有压倒性的丰富物理性质，例如巨磁电阻、磁电子相分离、莫特跃迁、自旋电子相关、磁电效应等。调整组成过渡金属阳离子之间的交换相互作用和磁电子特征的操作方法将包括通过改变阳离子亚晶格掺杂电子或空穴，通过外延薄膜沉积引入外部应变以及通过热处理或电化学可逆插入和提取阴离子（O2-或F-）。我们集团在薄膜沉积，磁性，磁电子/离子学和磁性电化学控制方面的长期经验，结合新获得的heo专业知识，将用于实现“具有heo的新型磁电子学”的设想目标。

Multicomponent high entropy oxides (HEOs) represent a group of single phase oxide solid solutions consisting of five or more cations in nearly equiatomic proportion. Although the field of HEO is barely five years old, several intriguing structural and functional features of different classes of HEOs have been already reported, which include some of our own pioneering investigations performed within the framework of the initial funding period. More specific achievements of the initial funding period are as follows: (a) discovery of rare-earth transition metal based perovskite-HEOs (P-HEOs) and anionic disordered high entropy oxyfluorides (HEOFs), (b) demonstration of the superior electrochemical performance of rocksalt-HEOs and HEOFs as anodes and cathodes for Li-ion batteries (d) elucidation of the reversibly controlled band structure of fluorite-HEOs and finally, (e) the observation of exotic magnetic phenomena stemming from the extreme chemical disorder in P-HEOs, such as exchange bias, large magneto-crystalline anisotropy, large coercive fields at room temperature, etc. These results are the outcome of rather fundamental but diverse investigations, intended to scout whether the field of HEOs is worth studying. In effect, this pioneering research has already highlighted the plethora of unprecedented physico-chemical phenomena that the multicomponent high entropy based design approach can offer. The main thrust of this research proposal will be the introduction of a new class of materials to the field of magneto-electronics with either enhanced or hitherto unknown functionalities by using chemical disorder on both cationic and anionic sites offered by the high entropy based approach. The group of rare-earth transition metal P-HEOs is chosen as the primary HEO-class for this exploration based on the already obtained results, which indicate their strong inherent connection between the chemical disorder, prominent structural distortions and stabilization of unusual spin-electronic states. Naturally, P-HEOs as a material class is also an optimal choice due to the overwhelming richness of the physical properties of the parent perovskites, e.g., colossal magnetoresistance, magneto-electronic phase separation, Mott transitions, spin-electron correlations, magneto-electric effect, etc. The modi operandi for tuning the exchange interactions among the constituent transition metal cations and thereby the magneto-electronic features will include electron or hole doping by altering the cationic sub-lattice(s), external strain introduction by epitaxial thin film deposition and reversible insertion and extraction of anions (O2- or F-) via heat treatments or electrochemistry. Our group’s long term experience on thin film deposition, magnetism, magneto-electronics/-ionics and electrochemical control of magnetism in combination with the newly gained expertise on HEOs will be utilized to achieve the envisaged goal of “novel magneto-electronics with HEOs”.