Crystal and electronic structure engineering of tin monoxide by external pressure

Abstract

Although tin monoxide (SnO) is an interesting compound due to its p-type conductivity, a widespread application of SnO has been limited by its narrow band gap of 0.7 eV. In this work, we theoretically investigate the structural and electronic properties of several SnO phases under high pressures through employing van der Waals (vdW) functionals. Our calculations reveal that a metastable SnO (β-SnO), which possesses space group P21/c and a wide band gap of 1.9 eV, is more stable than α-SnO at pressures higher than 80 GPa. Moreover, a stable (space group P2/c) and a metastable (space group Pnma) phases of SnO appear at pressures higher than 120 GPa. Energy and topological analyses show that P2/c-SnO has a high possibility to directly transform to β-SnO at around 120 GPa. Our work also reveals that β-SnO is a necessary intermediate state between high-pressure phase Pnma-SnO and low-pressure phase α-SnO for the phase transition path Pnma-SnO →β-SnO → α-SnO. Two phase transition analyses indicate that there is a high possibility to synthesize β-SnO under high-pressure conditions and have it remain stable under normal pressure. Finally, our study reveals that the conductive property of β-SnO can be engineered in a low-pressure range (0–9 GPa) through a semiconductor-to-metal transition, while maintaining transparency in the visible light range.

Electron-Deficient-Type Electride Ca5Pb3: Extension of Electride Chemical Space

“…Pressure is effective to manipulate the electronic structure of compounds. ,− They may induce structural variations or electron redistribution, which often leads to new phases. The influence of pressure on the electronic properties of Ca 5 Pb 3 was carefully examined.…”

High-Pressure Phase Diagram of the Ti–O System

“…Variable-composition search allowed all Ti x O y compositions under the constraint of fewer than 16 atoms in the primitive cell. Global optimization was performed using USPEX, a powerful tool for predicting novel unknown materials that has successfully found many new crystalline phases of various materials, − in particular under extreme conditions. ,,, All of the structures of the first generation were produced using the random symmetric structure generator and were relaxed using VASP, and the first convex hull was built on the basis of the enthalpies of the relaxed structures. Structures closest to the convex hull were used as parents for the generation of new structures, which were also relaxed, leading to an updated convex hull, after which the next generation of structures was found, and so on.…”

Electride Formation in Ba–P System and the Unexpected Structure Transition of Electrides under Pressure

“…It is well known that external high pressures can effectively reduce atom distances and modify the strength of interatomic interactions, thus leading to the change of phase stability through electronic structures . Therefore, a high pressure can bring materials with many excellent physical and chemical properties that cannot be obtained at ambient pressure. − For example, some solids that are nonmetallic or insulating at ambient conditions were reported to be converted into superconductors (including inert gases) upon applying high pressures . Moreover, weak π bonds, van der Waals bonds, and hydrogen bonds can be transformed to strong covalent or ionic bonds under high pressures, which can stabilize exotic stoichiometries that would not be expected at atmospheric pressures and increase coordination numbers to form new structures. ,, …”

“…The identification of typical electrides, such as C12A7:e – and Ca 2 N:e – , was done by experimental screening. , Recently, high-throughput structure search algorithm combined with first-principles calculations has played an increasingly important role in discovering new materials including electrides. ,,,− For example, 1D electride Sr 5 P 3 was predicted using the evolutionary structure search method USPEX − in the strontium–phosphorus (Sr–P) system and then was experimentally synthesized . It is known that alkaline earth (AE) metals, calcium (Ca) and barium (Ba), have similar outer electron structures and electronegativities with Sr.…”