Structural Phase Transitions and Quantum Dots Regulation of Perovskite Stannates

Abstract

First-principles calculations in conjunction with the CALYPSO structure search method are performed to investigate the structural phase transitions of the perovskite stannates ASnO 3 (A = Ca, Sr, and Ba) under hydrostatic pressure up to 100 GPa. Two reconstructive phase transitions appear in CaSnO 3 , that is, from a perovskite state (Pv-Pnma) to a novel state that belongs to the post-perovskite family (pPv-Cmcm) and then undergoing another reconstructive transition to the so-called post-post-perovskite state (ppPv-Pnma) at higher pressure. In contrast, SrSnO 3 directly changes from Pv-Pnma phase to ppPv-Pnma phase under high pressure. However, BaSnO 3 only retains the ideal cubic perovskite structure up to 100 GPa without a phase transition. Subsequently, based on time-dependent density functional theory (TDDFT), quantum dots (QDs) fabricated by the pressure-induced stable structures of ASnO 3 interacting with ultrafast laser pulses are investigated. Strikingly, compared with traditional perovskite QDs fabricated by simple structure (Pm3̅ m), pPv-QDs based on the stable phase pPv-Cmcm of CaSnO 3 occur an obvious insulator−metal transition within a wide range of laser wavelengths and show enhanced optical absorption through size adjustment. In particular, CaSnO 3 pPv-QDs under high-intensity lasers exhibit nonvolatile memory characteristics, which demonstrates the potential applications for memory units and data storage devices.

Pressure induced phase transitions of bulk CsGeCl3 and ultrafast laser pulse induced excited-state properties of CsGeCl3 quantum dots

“…It may be due to the wavelength of 792 nm being close to the intrinsic frequency of the three CsGeCl 3 QDs, which makes photocarriers achieve higher resonance energy. 27,28,53…”

“…pPv-Cmcm, ppPv-Pnma, and so on). 28,29 However, for halide perovskite QDs, CsGeI 3 colloidal nanocrystals have been successfully synthesized with the R3m phase, and a host of investigations are mainly focused on the ground-state structures. 30,31 Regrettably, the investigations of CsGeCl 3 QDs are rarely reported.…”