A family of Zn k O k (k = 12, 16) cluster-assembled solid phases with novel structures and properties has been characterized utilizing a bottom-up approach with density functional calculations. Geometries, stabilities, equation of states, phase transitions, and electronic properties of these ZnO polymorphs have been systematically investigated. First-principles molecular dynamics (FPMD) study of the two selected building blocks, Zn 12 O 12 and Zn 16 O 16 , with hollow cage structure and large HOMO−LUMO gap shows that both of them are thermodynamically stable enough to survive up to at least 500 K. Via the coalescence of building blocks, we find that the Zn 12 O 12 cages are able to form eight stable phases by four types of Zn 12 O 12 −Zn 12 O 12 interactions, and the Zn 16 O 16 cages can bind into three phases by the Zn 16 O 16 −Zn 16 O 16 links of H′, C′, and S′. Among these phases, six ones are reported for the first time. This has greatly extended the family of ZnO nanoporous phases. Notably, some of these phases are even more stable than the synthesized metastable rocksalt ZnO polymorph. The hollow cage structure of the corresponding building block Zn k O k is well preserved in all of them, which leads to their low-density nanoporous and high flexibility features. In addition the electronic integrity (wide-energy gap) of the individual Zn k O k is also retained. Our calculation reveals that they are all semiconductor with a large direct or indirect band gap. The insights obtained in this work are likely to be general in II−VI semiconductor compounds and will be helpful for extending the range of properties and applications of ZnO materials.
Since most of the existing pristine
two-dimensional (2D) materials are either intrinsically nonmagnetic
or magnetic with small magnetic moment per unit cell and weak strength
of magnetic coupling, introducing transition metal atoms in various
nanosheets has been widely used for achieving a desired 2D magnetic
material. However, the problem of surface clustering for the doped
transition metal atoms is still challenging. Here we demonstrate via
first-principles calculations that the recently experimentally characterized
endohedral silicon cage V@Si12 clusters can construct two
types of single cluster sheets exhibiting hexagonal porous or honeycomb-like
framework with regularly and separately distributed V atoms. For the
ground state of these two sheets, the preferred magnetic coupling
is found to be ferromagnetic due to a free-electron-mediated mechanism.
By using external strain, the magnetic moments and strength of magnetic
coupling for these two sheets can be deliberately tuned, which would
be propitious to their advanced applications. More attractively, our
first-principles molecular dynamics simulations show that both the
structure and strength of ferromagnetic coupling for the pristine
porous sheet are stable enough to survive at room temperature. The
insights obtained in this work highlight a new avenue to achieve 2D
silicon-based spintronics nanomaterials.
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