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ZrS2 is trigonal omega structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one ZrS2 sheet oriented in the (0, 0, 1) direction. Zr4+ is bonded to six equivalent S2- atoms to form edge-sharing ZrS6 octahedra. All Zr–S bond lengths are 2.58 Å. S2- is bonded in a distorted T-shaped geometry to three equivalent Zr4+ atoms.
LiZr2S4 crystallizes in the monoclinic P2/m space group. The structure is three-dimensional. Li1+ is bonded to six S2- atoms to form LiS6 octahedra that share corners with six equivalent ZrS6 octahedra, edges with two equivalent LiS6 octahedra, and edges with six ZrS6 octahedra. The corner-sharing octahedra tilt angles range from 1–2°. All Li–S bond lengths are 2.64 Å. There are two inequivalent Zr+3.50+ sites. In the first Zr+3.50+ site, Zr+3.50+ is bonded to six S2- atoms to form ZrS6 octahedra that share corners with six equivalent LiS6 octahedra, edges with two equivalent LiS6 octahedra, and edges with six ZrS6 octahedra. The corner-sharing octahedra tilt angles range from 1–2°. There are two shorter (2.58 Å) and four longer (2.61 Å) Zr–S bond lengths. In the second Zr+3.50+ site, Zr+3.50+ is bonded to six S2- atoms to form ZrS6 octahedra that share edges with four equivalent LiS6 octahedra and edges with six ZrS6 octahedra. There are four shorter (2.59 Å) and two longer (2.60 Å) Zr–S bond lengths. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded to two equivalent Li1+ and three Zr+3.50+ atoms to form a mixture of edge and corner-sharing SLi2Zr3 square pyramids. In the second S2- site, S2- is bonded in a rectangular see-saw-like geometry to one Li1+ and three Zr+3.50+ atoms.
Abstract Transition metal dichalcogenides have shown great potential for next-generation electronic and optoelectronic devices. However, native oxidation remains a major issue in achieving their long-term stability, especially for Zr-containing materials such as ZrS 2 . Here, we develop a first principles-informed reactive forcefield for Zr/O/S to study oxidation dynamics of ZrS 2 . Simulation results reveal anisotropic oxidation rates between (210) and (001) surfaces. The oxidation rate is highly dependent on the initial adsorption of oxygen molecules on the surface. Simulation results also provide reaction mechanism for native oxide formation with atomistic details. Graphic Abstract
In contrast to two-dimensional (2D) monolayer materials, van der Waals layered transition metal dichalcogenides exhibit rich polymorphism, making them promising candidates for novel superconductor, topological insulators and electrochemical catalysts. Here, we highlight the role of hydrostatic pressure on the evolution of electronic and crystal structures of layered ZrS2. Under deviatoric stress, our electrical experiments demonstrate a semiconductor-to-metal transition above 30.2 GPa, while quasi-hydrostatic compression postponed the metallization to 38.9 GPa. Both X-ray diffraction and Raman results reveal structural phase transitions different from those under hydrostatic pressure. Under deviatoric stress, ZrS2 rearranges the original ZrS6 octahedra into ZrS8 cuboids at 5.5 GPa, in which the unique cuboids coordination of Zr atoms is thermodynamically metastable. The structure collapses to a partially disordered phase at 17.4 GPa. These complex phase transitions present the importance of deviatoric stress on the highly tunable electronic properties of ZrS2 with possible implications for optoelectronic devices.
(ZrS2)2N2 is trigonal omega-derived structured and crystallizes in the trigonal R3m space group. The structure is two-dimensional and consists of three ammonia molecules and three ZrS2 sheets oriented in the (0, 0, 1) direction. In each ZrS2 sheet, Zr3+ is bonded to six S2- atoms to form edge-sharing ZrS6 octahedra. There are three shorter (2.58 Å) and three longer (2.59 Å) Zr–S bond lengths. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted T-shaped geometry to three equivalent Zr3+ atoms. In the second S2- site, S2- is bonded in a distorted T-shaped geometry to three equivalent Zr3+ atoms.
ZrS2TiS2 is trigonal omega-derived structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one TiS2 sheet oriented in the (0, 0, 1) direction and one ZrS2 sheet oriented in the (0, 0, 1) direction. In the TiS2 sheet, Ti4+ is bonded to six equivalent S2- atoms to form edge-sharing TiS6 octahedra. All Ti–S bond lengths are 2.47 Å. S2- is bonded in a distorted T-shaped geometry to three equivalent Ti4+ atoms. In the ZrS2 sheet, Zr4+ is bonded to six equivalent S2- atoms to form edge-sharing ZrS6 octahedra. All Zr–S bond lengths are 2.56 Å. S2- is bonded in a distorted T-shaped geometry to three equivalent Zr4+ atoms.
Moving beyond the engineering of known materials and elemental substitution within common structure types is critical for designing unique properties. Here, we present a new homologous series, ACu 2 Q 2 (MQ 2 ) n (A = Sr, Ba, 2Na; MQ 2 = ZrS2, HfSe 2 ), establishing 11 new members. In β-BaCu 2 Q 2 and Na 2 Cu 2 Se 2 (n = 0), the [Cu 2 Q 2 ] 2– motifs extend in two dimensions, whereas those in α-BaCu 2 Q 2 extend in three dimensions. Hence, there are two structural evolutions within the ACu 2 Q 2 (MQ 2 )n family driven by the polymorphism of the host structures. MQ 2 (n → ∞) displays 2D layers of edge-sharing [MQ 6 ] 8– octahedra that are 1-octahedron-thick and connected via van der Waals bonding. Each insertion of MQ 2 into ACu 2 Q 2 incorporates [MQ 6 ] 8– octahedra extending infinitely in one direction, confined to being 1-octahedron-thick in the second direction, with n controlling the number of [MQ 6 ] 8– octahedra in the third direction. Therefore, increasing n predictively expands the [Cu 2 MnQ 2n+2 ] 2– network in the direction controlled by n and relative to the A + /A 2+ ions. We demonstrate that for a given set of elements, one can enforce a “Host(Insertion)n” formula to systematically evolve both crystal and electronic structures from the host (n = 0) to the insertion (n → ∞) materials through intermediate values of n. Specifically, the energetic misalignment of the electronic band extrema of the parents predictively determines the band extrema and the resulting band gaps of all intermediate n members.
Transition metal dichalcogenides (TMD) combine semiconducting properties with stability and are therefore widely studied for future microelectronic devices. However, applications require integration with a suitable dielectric at a planar, defect-free interface. For Hf- and Zr-based TMDs, the good dielectric properties of hafnia and zirconia imply that direct oxidation is a promising strategy, provided that a high-quality interface and suitable oxide morphology can be formed. Here, in this study, we investigate HfS 2 and ZrS 2 oxidation, aiming to understand pathways toward planar oxide layer formation and the mechanisms that determine the characteristics of the semiconductor/dielectric interface. We use conventional and environmental transmission electron microscopy to reveal changes in morphology and composition of the TMDs under different gaseous environments. We show that oxidation at ambient conditions causes compositional heterogeneities, with local replacement of S by O in both materials. Thermal oxidation causes desulfurization and formation of a smooth but defective oxide layer. In contrast, plasma oxidation appears the best-suited to forming a controlled TMD/dielectric interface with a smooth oxide layer and without major defects. These results provide insight into the opportunities available from HfS 2 and ZrS 2 through oxidation and suggest a materials processing strategy for electronic device fabrication.