Ferroelastic Domains in a CsPbBr₃ Single Crystal and Their Phase Transition Characteristics: An in Situ TEM Study

Abstract

The all-inorganic halide perovskite CsPbBr3 has attracted significant attention for applications of high-performance and stable solar cells, light-emitting diodes (LEDs), and photoelectric and X-/γ-ray detectors. The discrepant photoelectric properties are confusing, which strongly implies that the perovskite is sensitive to defects. Here, novel and ubiquitous defects, “twin domains”, are reported in solution-grown CsPbBr3 single crystals on the basis of X-ray diffraction techniques, optical microscopy, and transmission electron microscopy (TEM). Two kinds of orthorhombic domain structures, {121} reflection twins and 90° rotations along [101̅], are identified in as-grown CsPbBr3 crystals. In situ TEM results indicate that these domains are ferroelastic, which are related to the spontaneous strain induced by a phase transition. During a phase transition from parent cubic (m3̅m) to tetragonal (4/mmm), the loss of cubic {110} reflection planes, the 4-fold rotation axis (4), or the 3-fold rotoinversion axis (3̅) could act as a twin law and account for the appearance of domain walls. Further reduction of symmetry to orthorhombic (mmm) and the losses of the tetragonal 4-fold rotation axis (4) and mirror plane {101} lead to the emergence of [101̅] rotations and {101} reflection twins, respectively. Our work not only enhances the understanding of defects in CsPbBr3, which opens the door for the further optimization of photoelectric applications, but also provides a way to tailor it.

In Situ Imaging of Ferroelastic Domain Dynamics in CsPbBr3 Perovskite Nanowires by Nanofocused Scanning X-ray Diffraction

“…29−32 Likewise, ferroelastic domains could be formed in CsPbBr 3 single crystals induced by phase transitions. 33 Ferroelectric materials additionally exhibit electric polarization, which could affect the performance of MHP solar cells. 34−37 Studying ferroelectricity and ferroelasticity in MHPs is therefore important, both for applications and for a fundamental understanding of these materials.…”

“…In ferroelastic materials, stress leads to the formation of domains with different crystal orientation . It has been demonstrated that ferroelasticity can be a key to induce domain formation in different structures, including epitaxial tetragonal phase perovskites. , If two interfacing domains have different lattice spacings, the domains will generally tilt due to the lattice mismatch at the domain walls. − Likewise, ferroelastic domains could be formed in CsPbBr 3 single crystals induced by phase transitions . Ferroelectric materials additionally exhibit electric polarization, which could affect the performance of MHP solar cells. − Studying ferroelectricity and ferroelasticity in MHPs is therefore important, both for applications and for a fundamental understanding of these materials.…”

“…XRD is also very sensitive to lattice tilt and can be used to measure domain tilts with extremely high precision. ,− Traditionally, the real-space resolution of XRD has been poor, but the recent development in X-ray optics has made it possible to focus X-rays down to the nanoscale. , Scanning XRD using a nanofocused beam has enabled studies of single nanocrystals and nanoscale devices − as well as static imaging of ferroelectric domains . However, dynamic in situ studies of ferroelastic or ferroelectric domains, which have a typical size of about 100 nm, , require a very small and bright X-ray focus. Here, we use the NanoMAX beamline, situated at the first diffraction-limited storage ring MAX IV, to study the dynamics of ferroelastic domains in CsPbBr 3 nanowires during temperature variations, and demonstrate how scanning nano-XRD with a 60 nm beam size can be used for high-resolution in situ imaging of nanoscale ferroelastic domains within a single MHP nanowire.…”

Lanthanide-doped inorganic halide perovskites (CsPbX3): novel properties and emerging applications

“…For the study of phase transitions in CsPbBr 3 , several methods, such as selected area electron diffraction (SAED), 74 neutron diffraction, 75 hightemperature X-ray diffraction, 76,77 and DSC, [76][77][78] have been used. Zhang et al 74 studied phase transition in single-crystal CsPbBr 3 (synthesized using inverse temperature crystallization method) using the SAED patterns monitored through transmission electron microscopy (TEM) at various temperatures. The SAED patterns at different temperatures are shown in Fig.…”

Ferroelastic Domains Enhanced the Photoelectric Response in a CsPbBr3 Single-Crystal Film Detector

“…Selecting an all-inorganic counterpart with controllable ferroic domains would help study their function on optoelectronic properties. A CsPbBr 3 single crystal is a promising candidate for γ-ray detection, − within which the existence of {121} reflection and 90° rotation ferroelastic twin domains has been demonstrated . Building the correlation between ferroelastic domains and optoelectronic properties in CsPbBr 3 should be a non-trivial task for understanding the mechanism behind the domain-adjusted optoelectronic properties.…”