Pressure-Regulated Dynamic Stereochemical Role of Lone-Pair Electrons in Layered Bi₂O₂S

Abstract

Lone-pair electrons (LPEs) ns2 in subvalent 14 and 15 groups lead to highly anharmonic lattice and strong distortion polarization, which are responsible for the groups’ outstanding thermoelectric and optoelectronic properties. However, their dynamic stereochemical role in structural and physical properties is still unclear. Here, by introducing pressure to tune the behavior of LPEs, we systematically investigate the lone-pair stereochemical role in a Bi2O2S. The gradually suppressed LPEs during compression show a nonlinear repulsive electrostatic force, resulting in two anisotropic structural transitions. An orthorhombic-to-tetragonal phase transition happens at 6.4 GPa, caused by the dynamic cation centering. This structural transformation effectively modulates the optoelectronic properties. Further compression beyond 13.2 GPa induces a 2D-to-3D structural transition due to the disappearance of the Bi-6s2 LPEs. Therefore, the pressure-induced LPE reconfiguration dominates these anomalous variations of lattice, electronic, and optical properties. Our findings provide new insights into the materials optimization by regulating the characters of LPEs.

Pressure‐Tailored Band Engineering for Significant Enhancements in the Photoelectric Performance of CsI3 in the Optical Communication Waveband

“…This is the first example of a pressure‐regulated spectral range for photoelectric materials. [ 22–24 ] This demonstrates that pressure variation is an effective way to modify the photoelectric performance of materials, which can be used to design photoelectric devices with a broad spectral detection range.…”

“…Pressure has been proven to be an effective means for tuning the photoelectronic properties of functional materials. [ 22–32 ] Significant enhancements of the photocurrent by three orders of magnitude in indirect bandgap materials Cs 2 PbI 2 Cl 2 [ 22 ] and BiO 2 S 2 [ 23 ] were realized by regulating the excitonic features and the dynamic stereochemical role of lone‐pair electrons under high pressure, respectively. In addition, direct bandgap materials are more suitable for photoelectronic applications because of their higher optical absorption coefficients compared with those of indirect bandgap materials.…”

“…However, experimentally realizing indirect‐direct bandgap transitions in bulk systems using external stimuli is still a considerable challenge. High pressure provides a powerful way to modulate the crystal and electronic structure, even successively modifying the bandgap of materials as strain engineering does, [ 22–24 ] which provides a potential technique to realize the regulation between the indirect and direct bandgap transitions and expand the detection bandwidth of photoelectric materials. Nevertheless, no research has achieved a giant pressure‐enhanced photocurrent of functional materials by regulating the type of optical transition and expanding the detection bandwidth from visible light to the optical communication waveband.…”

Pressure‐Driven Two‐Step Second‐Harmonic‐Generation Switching in BiOIO3

“…[9] According to previous studies, pressure is generally considered to suppress the lone-pair effect, and thus to influence the overall SHG property of materials. [10] Previously, we have observed the SHG "on-off" transition in the SHG-active CdMoTeO 6 by pressure-regulated lone-pair electrons. [11] Further exploration of this kind of materials has attracted our attention to a recently reported iodate BiOIO 3 , in which both the Bi 3 + and I 5 + cations contain the stereo-active lonepair electrons promising for achieving stepwise SHG switching under compression.…”

Pressure Engineering for Extending Spectral Response Range and Enhancing Photoelectric Properties of Iodine

“…As an effective means of tuning the physical and chemical properties of materials, high pressure can be used to modify photoelectric and related properties via adjustment of the atomic and electronic structures. [19][20][21][22][23][24][25][26][27][28][29][30] Pressure-induced photoelectric performance enhancement has been achieved for several photoelectric materials, such as ReS 2 , [19] KBiFe 2 O 5 , [20] PbBiO 2 Br, [21] and Bi 9 O 7.5 S 6 . [23] However, such enhancement is typically limited.…”