High‐Resolution In‐Situ Synchrotron X‐Ray Studies of Inorganic Perovskite CsPbBr₃: New Symmetry Assignments and Structural Phase Transitions

Abstract

Perovskite photovoltaic ABX 3 systems are being studied due to their high energy-conversion efficiencies with current emphasis placed on pure inorganic systems. In this work, synchrotron single-crystal diffraction measurements combined with second harmonic generation measurements reveal the absence of inversion symmetry below room temperature in CsPbBr 3 . Local structural analysis by pair distribution function and X-ray absorption fine structure methods are performed to ascertain the local ordering, atomic pair correlations, and phase evolution in a broad range of temperatures. The currently accepted space group assignments for CsPbBr 3 are found to be incorrect in a manner that profoundly impacts physical properties. New assignments are obtained for the bulk structure: Im3 (above ≈410 K), P2 1 /m (between ≈300 K and ≈410 K), and the polar group Pm (below ≈300 K), respectively. The newly observed structural distortions exist in the bulk structure consistent with the expectation of previous photoluminescence and Raman measurements. High-pressure measurements reveal multiple low-pressure phases, one of which exists as a metastable phase at ambient pressure. This work should help guide research in the perovskite photovoltaic community to better control the structure under operational conditions and further improve transport and optical properties.

Investigation of phase transition, mechanical behavior and lattice thermal conductivity of halogen perovskites using machine learning interatomic potentials

“…58 They revealed that a first-order transition from the cubic phase to tetragonal phase at 403 K, and a second-order change from the tetragonal phase to orthorhombic phase at 361 K. Recently, Liu et al investigated structural phase transitions of CsPbBr 3 using a high-resolution in-situ synchrotron XRD method. 59 They observed a bulk structure with a space group of cubic Im 3̄ above 410 K, which was extremely similar to a previously reported Pm 3̄ m unit cell. The cubic CsPbBr 3 then underwent a transition to monoclinic P 2 1 / m between 300 K and 410 K, and to the monoclinic polar group Pm below 310 K. After confirmation, it was found that the β angle in monoclinic cells was close to 90°, which could be roughly considered the orthorhombic phase.…”

Polariscopy with optical near-fields

“…Phase transitions can be monitored spectroscopically by emission and absorption at the vibrational, rotational, and phonon spectral range from volumes comparable to the wavelength of light 20,21 as well as by diffraction of synchrotron Xrays or free-electron lasers (X-FELs). [22][23][24] Here, we validate the hypothesis of polarisation analysis using non-propagating evanescent light. Anisotropy of absorbance is determined by measuring the difference between two perpendicular s-and p-polarisation components, in amplitude and phase, from the fit of the angular dependence of transmittance through an ATR setup.…”

“…Phase transitions can be monitored spectroscopically by emission and absorption at the vibrational, rotational, and phonon spectral range from volumes comparable to the wavelength of light 20,21 as well as by diffraction of synchrotron X-rays or free-electron lasers (X-FELs). 22–24…”

Anti-Stokes photoluminescence of perovskite CsPbBr-=SUB=-3-=/SUB=- nanocrystals in a fluorophosphate glass matrix

“…As the temperature increases further, the shift of the bands slows down, which is associated with phase transitions in the CsPbBr 3 perovskite [36]. Simultaneously with the shift, the PL bands are broadened, probably due temperature range T = 10−170 K. The linear dependence is typical for the interaction with acoustic phonons.…”