摘要
Superionic and electride behaviors in materials,which induce a variety of exotic physical properties of ions and electrons,are of great importance both in fundamental research and for practical applications.However,their coexistence in hot alkali-metal borides has not been observed.In this work,we apply first-principles structure search calculations to identify eight Na-B compounds with host-guest structures,which exhibit a wide range of building blocks and interesting properties linked to the Na/B composition.Among the known borides,Na-rich Na9B stands out as the composition with the highest alkali-metal content,featuring vertex-and face-sharing BNa16 polyhedra.Notably,it exhibits electride characteristics and transforms into a superionic electride at 200 GPa and 2000 K,displaying unusual Na atomic diffusion behavior attributed to the modulation of the interstitial anion electrons.It demonstrates semiconductor behavior in the solid state,and metallic properties associated with Na 3p/3s states in the superionic and liquid regions.On the other hand,B-rich NaB7,consisting of a unique covalent B framework,is predicted to exhibit low-frequency phonon-mediated superconductivity with a T_(c) of 16.8 K at 55 GPa.Our work advances the understanding of the structures and properties of alkali-metal borides.
基金
This work was supported by the Natural Science Foundation of China under Grant No.21573037
the Postdoctoral Science Foundation of China under Grant No.2013M541283
the Natural Science Foundation of Hebei Province(Grant No.B2021203030)
the Science and Technology Project of Hebei Education Department(Grant Nos.JZX2023020 and QN2023246)
A.B.acknowledges financial support from the Spanish Ministry of Science and Innovation(Grant No.PID2019-105488GB-I00)
the Department of Education,Universities and Research of the Basque Government and the University of the Basque Country(Grant No.IT1707-22)
This work was carried out at the National Supercomputer Center in Tianjin,and the calculations were performed on TianHe-1(A).