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论文类型：期刊论文

发表时间：2015-01-01

发表刊物：RSC ADVANCES

收录刊物：SCIE、EI、Scopus

卷号：5

期号：59

页面范围：48012-48023

ISSN号：2046-2069

摘要：We investigated the high-pressure structures and properties of iron tetraborides (FeB4) using a combination of an ab initio high-throughput search and a particle-swarm optimization algorithm for crystal structure prediction. We found that, under compression, the boron sublattice in FeB4 from the buckled boron layer first polymerizes into B-4 tetrahedral clusters and then forms cubo-octahedral B-12 clusters. At 55 GPa, the orthorhombic crystal structure with a Pnnm space group (58-FeB4) transforms into a tetragonal I4(1)/acd structure (142-FeB4), which is stable within a wide pressure range up to 695 GPa. Then, a cubic Im (3) over barm phase (229-FeB4) emerges at higher pressures up to at least 1 TPa. The computed Vicker's hardnesses of 58-, 142-, and 229-FeB4 are 61.58, 47.44, and 50.87 GPa, respectively. All of them can be considered as superhard materials. Compared to the previously reported 58-FeB4 as a superhard superconductor, the B-4 tetrahedral cluster-based 142-FeB4 is a superhard semiconductor with an indirect band gap of 1.34 eV. The pressure-induced metal-to-semiconductor transition can be related to a unique Fe-B-B three-center covalent bond. Moreover, 229-FeB4, which is composed of cubooctahedral B-12 clusters, is ferromagnetic with a magnetic moment of 0.929 mu(B) per Fe atom at ambient pressure. The magnetic moment will decrease rapidly with increasing pressure and be completely quenched as pressure exceeds 40 GPa. The pressure-induced evolution of boron cluster units not only adds new features to boron chemistry, but also gives rise to novel superhard semiconductors or ferromagnetic materials. Moreover, our results may inspire further experimental and theoretical interest in designing new materials using clusters as pseudo-atoms with expected properties.