The influence of deuteration on the crystal structure of hybrid halide perovskites: a temperature-dependent neutron diffraction study of FAPbBr₃

Abstract

This paper discusses the full structural solution of the hybrid perovskite formamidinium lead tribromide (FAPbBr3) and its temperature‐dependent phase transitions in the range from 3 K to 300 K using neutron powder diffraction and synchrotron X‐ray diffraction. Special emphasis is put on the influence of deuteration on formamidinium, its position in the unit cell and disordering in comparison to fully hydrogenated FAPbBr3. The temperature‐dependent measurements show that deuteration critically influences the crystal structures, i.e. results in partially‐ordered temperature‐dependent structural modifications in which two symmetry‐independent molecule positions with additional dislocation of the molecular centre atom and molecular angle inclinations are present.

Phase Diagram and Cation Dynamics of Mixed MA1-xFAxPbBr3 Hybrid Perovskites

“…30,42 A substantial degree of disorder of FA cations was found even at 10 K temperature. 41 Our results show that mixing of these compounds significantly suppresses the structural phase transitions resulting in stabilization of the cubic phase. We observe drastic perturbations of the cation dynamics and long-range order upon mixing, which are reflected as the pronounced changes in the dielectric response.…”

“…This indicates that either the symmetry change is suppressed at the maximal mixing level or the changes are too subtle to be detected with our XRD setup. We used our experimental data together with the information provided in the literature [35][36][37]41,42 to construct the temperature-composition phase diagram of MA 1-x FA x PbBr 3 (see Figure 2). The MA-rich region of the phase diagram is in a qualitative agreement with the phase diagrams reported for the related MA 1-x FA x PbI 3 perovskite system.…”

“…30 Note that other studies also observed a significant FA cation disorder at low temperatures in FAPbBr 3 and FAPbI 3 perovskites. 41,42,49…”

“…Recent studies reported two transitions at about 266 K and 153 K, which correspond to cubic (P m3m) → tetragonal (P 4/mbm) → orthorhombic (P nma) symmetry-lowering. [39][40][41] Three additional isostructural transitions were observed at 182, 162 and 118 K that involve changes of the FA cation dynamics and are not resolved crystallographically. 30,42 A substantial degree of disorder of FA cations was found even at 10 K temperature.…”

Dynamics & Spectroscopy with Neutrons—Recent Developments & Emerging Opportunities

“…A substantial part of our current understanding of the structural properties of these materials stems from Neutron Diffraction (ND) [ 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 ]. Most importantly, the use of neutron Laue diffractometers, operating both at pulsed (e.g., SXD at ISIS, UK [ 95 ]; TOPAZ at SNS [ 96 ], US; SENJU at J-PARC, JP [ 97 ]) and continuous neutron sources (e.g., KOALA at ANSTO, AU [ 98 ]; FALCON at BER-2, DE [ 99 ]—currently transferred to the spallation source SINQ, CH) provide the means to precisely explore OHP single-crystal samples from a crystallographic perspective.…”