Static and Dynamic Disorder in Formamidinium Lead Bromide Single Crystals

TL;DR

This study reveals that formamidinium lead bromide exhibits intrinsic local static disorder in its inorganic sub-lattice, affecting its structural dynamics and phase transitions, as shown through combined spectroscopic and diffraction techniques.

Contribution

It uncovers the coexistence of static disorder with a well-defined average structure in this perovskite, using multi-method analysis across a wide temperature range.

Findings

Static disorder influences phase transitions

Inorganic sub-lattice dynamics are temperature-dependent

Static disorder persists at low temperatures

Abstract

We show that formamidinium lead bromide is unique among the halide perovskite crystals because its inorganic sub-lattice exhibits intrinsic local static disorder that co-exists with a well-defined average crystal structure. Our study combines THz-range Raman-scattering with single-crystal X-ray diffraction and first-principles calculations to probe the inorganic sub-lattice dynamics evolution with temperature in the range of 10-300 K. The temperature evolution of the Raman spectra shows that low-temperature, local static disorder strongly affects the crystal's structural dynamics and phase transitions at higher temperatures.