Symmetric Breakage-Induced Semimetallic State: Polymorphism in Ruthenate Nanosheets

Abstract

Atomic arrangements and their symmetries govern the physical properties of materials, including nanosheets that are low-dimensional nanomaterials. Although they have the same composition, symmetric changes associated with atomic displacements sometimes induce unexpected physical properties. Herein, we report that symmetric breakage induces a semimetallic state in chemically exfoliated ruthenate nanosheets. The atomic arrangements and symmetries are determined by a pair distribution function (PDF); subsequently, the physical properties are discussed using ab initio calculations and resistivity measurements. Ruthenate nanosheets can adopt an electronic structure similar to that of graphene owing to symmetric breakage. We experimentally confirmed the polymorphism in ruthenate nanosheets that highlights the importance of symmetric analysis, even in low-dimensional materials.

Thermal and Chemical Phase Engineering of Two-Dimensional Ruthenate

“…The crystallization of the 1T′ phase in K-RuO 2 is most likely associated with the density and distribution of K + ions in the gallery. 27 Thus, interlayer engineering is required for their selective synthesis. It is notable that the smaller size of Na + (0.1 nm) compared with K + (0.14 nm) at the interlayer gallery resulted in a 2D hexagonal 1T phase with higher symmetry.…”

“…The fact that no phase transition was detected from the 1T phases to the 1T′ or 1H phases indicates that the recently found 1T′ and 1H phases could be energetically less favorable than the oblique 1T phase in the nanosheet form. The crystallization of the 1T′ phase in K-RuO 2 is most likely associated with the density and distribution of K + ions in the gallery . Thus, interlayer engineering is required for their selective synthesis.…”

“…Consequently, they hypothesized that exfoliation provides some driving force for the 1T−1H phase transition. More recently, Sonobe et al revisited the structure of K-RuO 2 and its exfoliated nanosheets, 27 finding that in contrast to Ko's work, the host layers showed a 1T′-phase structure (Figure 1e), although both authors adequately refined the XRD patterns of the synthesized K-RuO 2 samples. Finally, they demonstrated by means of a pair distribution function analysis that the 1T′ phase was preserved after exfoliating the 1T′-phase K-RuO 2 .…”

“…Consequently, further study is required on the crystalline phase of nanosheets derived from 1T-phase K-RuO 2 and on the origin of the unusual 1T-to-1H phase transition. On the basis of well-defined and controlled crystalline phases of ruthenate nanosheets, more experimental studies must be conducted to unveil the relationship between the crystalline phase and the electronic structure. For example, DFT calculations have inconsistently predicted that 1T-phase ruthenate nanosheets have either metallic electronic , or semiconducting states No experimental studies have addressed the stability of the possible oblique 1T, hexagonal 1T, 1T′, and 1H phases of ruthenate nanosheets.…”

“…On the basis of well-defined and controlled crystalline phases of ruthenate nanosheets, more experimental studies must be conducted to unveil the relationship between the crystalline phase and the electronic structure. For example, DFT calculations have inconsistently predicted that 1T-phase ruthenate nanosheets have either metallic electronic , or semiconducting states …”