Metal‐to‐Semiconductor Transition and Electronic Dimensionality Reduction of Ca₂N Electride under Pressure

Abstract

The discovery of electrides, in particular, inorganic electrides where electrons substitute anions, has inspired striking interests in the systems that exhibit unusual electronic and catalytic properties. So far, however, the experimental studies of such systems are largely restricted to ambient conditions, unable to understand their interactions between electron localizations and geometrical modifications under external stimuli, e.g., pressure. Here, pressure‐induced structural and electronic evolutions of Ca2N by in situ synchrotron X‐ray diffraction and electrical resistance measurements, and density functional theory calculations with particle swarm optimization algorithms are reported. Experiments and computation are combined to reveal that under compression, Ca2N undergoes structural transforms from R 3true¯ m symmetry to I 4true¯2d phase via an intermediate Fd 3true¯ m phase, and then to Cc phase, accompanied by the reductions of electronic dimensionality from 2D, 1D to 0D. Electrical resistance measurements support a metal‐to‐semiconductor transition in Ca2N because of the reorganizations of confined electrons under pressure, also validated by the calculation. The results demonstrate unexplored experimental evidence for a pressure‐induced metal‐to‐semiconductor switching in Ca2N and offer a possible strategy for producing new electrides under moderate pressure.

Vacancies and dopants in two-dimensional tin monoxide: An ab initio study

“…This suggests that semiconducting properties may be achieved with appropriate tailoring of the concentration and/or distribution of nitrogen dopants in the system. Besides, mechanical deformation by strain or pressure has also been shown to induce metal-tosemiconductor switching in a variety of materials [55][56][57] and can thus offer a complementary means for promoting electron reorganization. This unique finding highlights exciting opportunities in the Sn-O-N ternary system and may lead to useful applications in photocatalysis and high-performance optoelectronics.…”

Predicting the structure and stability of titanium oxide electrides

“…14,15 Upon compression, Ca 2 N experiences a phase transition from a 2D electride to a semiconducting 0D electride with the formation of anionic electrons localized in atom-sized cavities, 16 which was later on confirmed by a subsequent experiment. 17 For decades, TiO 2 has been considered as a technically important material that is known to be an efficient photocatalyst for a wide range of applications (e.g., air and water purification, hydrogen evolution, and photoelectrochemical conversion, etc.). Other stoichiometries in Ti-O materials, especially for O-rich Ti-O materials (e.g., TiO, Ti 2 O 3 , and TiO 2 ) in different forms and types, also show the great potential as photocatalysts, together with other applications as ultrahard 18 and ultrastiff 19 materials.…”

Floating Interlayer and Surface Electrons in 2D Materials: Graphite, Electrides, and Electrenes

“…Applying hydrostatic pressure to a Q2DE initially compresses the crystal in the c ‐direction, [ 130 ] but a further increase in pressure will trigger nontrivial phase transitions, as shown in Figure . [ 130–132 ] A combined computational–experimental study for AE 2 N ( AE = Ca, Sr, and Ba) showed that the low‐pressure rhombohedral phase () transforms into a cubic phase () at 2.8 GPa. [ 132 ] The transformation causes the ILB to disappear, forcing the excess electrons out of the interlayer space to channel‐like voids.…”

“…[ 130–132 ] A combined computational–experimental study for AE 2 N ( AE = Ca, Sr, and Ba) showed that the low‐pressure rhombohedral phase () transforms into a cubic phase () at 2.8 GPa. [ 132 ] The transformation causes the ILB to disappear, forcing the excess electrons out of the interlayer space to channel‐like voids. The resulting material is a quasi‐1D electride with a semimetallic band structure.…”