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AgCd is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ag is bonded in a body-centered cubic geometry to eight equivalent Cd atoms. All Ag–Cd bond lengths are 2.94 Å. Cd is bonded in a body-centered cubic geometry to eight equivalent Ag atoms.
AgCd crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. Ag is bonded to six equivalent Ag and six equivalent Cd atoms to form distorted AgCd6Ag6 cuboctahedra that share corners with eighteen equivalent AgCd6Ag6 cuboctahedra, edges with six equivalent AgCd6Ag6 cuboctahedra, edges with twelve equivalent CdCd6Ag6 cuboctahedra, faces with eight equivalent AgCd6Ag6 cuboctahedra, and faces with twelve equivalent CdCd6Ag6 cuboctahedra. There are two shorter (2.99 Å) and four longer (3.12 Å) Ag–Ag bond lengths. There are four shorter (2.98 Å) and two longer (3.01 Å) Ag–Cd bond lengths. Cd is bonded to six equivalent Ag and six equivalent Cd atoms to form distorted CdCd6Ag6 cuboctahedra that share corners with eighteen equivalent CdCd6Ag6 cuboctahedra, edges with six equivalent CdCd6Ag6 cuboctahedra, edges with twelve equivalent AgCd6Ag6 cuboctahedra, faces with eight equivalent CdCd6Ag6 cuboctahedra, and faces with twelve equivalent AgCd6Ag6 cuboctahedra. There are two shorter (2.99 Å) and four longer (3.12 Å) Cd–Cd bond lengths.
AgCd crystallizes in the orthorhombic Cmmm space group. The structure is two-dimensional and consists of two AgCd sheets oriented in the (0, 1, 0) direction. Ag is bonded in a 8-coordinate geometry to four equivalent Cd atoms. All Ag–Cd bond lengths are 2.94 Å. Cd is bonded in a 8-coordinate geometry to four equivalent Ag atoms.
AgCd crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are three inequivalent Ag sites. In the first Ag site, Ag is bonded to six equivalent Ag and six equivalent Cd atoms to form AgCd6Ag6 cuboctahedra that share corners with twelve AgCd6Ag6 cuboctahedra, edges with twelve AgCd6Ag6 cuboctahedra, edges with twelve equivalent CdCd6Ag6 cuboctahedra, faces with six equivalent AgCd6Ag6 cuboctahedra, and faces with twelve equivalent CdCd6Ag6 cuboctahedra. All Ag–Ag bond lengths are 3.06 Å. All Ag–Cd bond lengths are 3.01 Å. In the second Ag site, Ag is bonded to six equivalent Ag and six Cd atoms to form AgCd6Ag6 cuboctahedra that share corners with five equivalent CdCd10Ag6 cuboctahedra, corners with twelve AgCd6Ag6 cuboctahedra, edges with ten CdCd6Ag6 cuboctahedra, edges with twelve AgCd6Ag6 cuboctahedra, faces with six equivalent AgCd6Ag6 cuboctahedra, and faces with fifteen CdCd6Ag6 cuboctahedra. All Ag–Ag bond lengths are 3.06 Å. All Ag–Cd bond lengths are 3.01 Å. In the third Ag site, Ag is bonded to six equivalent Ag and six Cd atoms to form AgCd6Ag6 cuboctahedra that share corners with five equivalent CdCd10Ag6 cuboctahedra, corners with twelve AgCd6Ag6 cuboctahedra, edges with ten CdCd6Ag6 cuboctahedra, edges with twelve AgCd6Ag6 cuboctahedra, faces with six equivalent AgCd6Ag6 cuboctahedra, and faces with fifteen CdCd6Ag6 cuboctahedra. All Ag–Ag bond lengths are 3.06 Å. All Ag–Cd bond lengths are 3.01 Å. There are two inequivalent Cd sites. In the first Cd site, Cd is bonded to six Ag and six equivalent Cd atoms to form CdCd6Ag6 cuboctahedra that share corners with twelve CdCd6Ag6 cuboctahedra, edges with twelve AgCd6Ag6 cuboctahedra, edges with twelve CdCd6Ag6 cuboctahedra, faces with six equivalent CdCd6Ag6 cuboctahedra, and faces with twelve AgCd6Ag6 cuboctahedra. All Cd–Cd bond lengths are 3.06 Å. In the second Cd site, Cd is bonded to six Ag and ten equivalent Cd atoms to form CdCd10Ag6 cuboctahedra that share corners with ten AgCd6Ag6 cuboctahedra, corners with twelve CdCd6Ag6 cuboctahedra, edges with eight AgCd6Ag6 cuboctahedra, edges with sixteen CdCd6Ag6 cuboctahedra, faces with sixteen equivalent CdCd10Ag6 cuboctahedra, and faces with eighteen AgCd6Ag6 cuboctahedra. There are a spread of Cd–Cd bond distances ranging from 3.06–6.11 Å.
As a brand new two-dimensional (2D) material with promising electronic properties, monolayer I-VII silver iodide (AgI) has the potential for future 2D electronic devices. To advance the development of such devices, the exploration of n-type and p-type conductivities of AgI is indispensable. With first-principles calculations, we systematically investigate the properties of intrinsic defects and extrinsic dopants in monolayer AgI, including atomic structural pictures, formation energies, and ionization energies to offer carriers. Considering the divergence in energies of charged defects in 2D materials when the traditional jellium scheme is used, we adopt an extrapolation approach to overcome the problem. The Ag vacancy (VAg) and Be substitution on Ag site (BeAg) are found to be the most promising p-type and n-type doping candidates, respectively. They could provide bound carriers for transport through the defect-bound band edge states, although the ionization energies are still larger than thermal energy at room temperature. Furthermore, negative-U behaviors are demonstrated in I vacancy (VI), Zn substitution on Ag site (ZnAg), and Cd substitution on Ag site (CdAg). The present work, for the first time, offers a detailed study of the defect physics in 2D I-VII monolayer semiconductor, laying the foundation for subsequent physics and device explorations based on these brand new 2D materials.