Bismuth-doping Alters Structural Phase Transitions in Methylammonium Lead Tribromide Single Crystals

TL;DR

Bismuth doping in methylammonium lead tribromide crystals reduces phase transition temperatures and simplifies phase behavior, likely due to induced compressive strain from substitutional Bi atoms, as shown by experimental and theoretical analysis.

Contribution

This study reveals how bismuth doping modifies phase transitions and crystal structure in MAPbBr3, providing insights into strain effects in perovskite materials.

Findings

Phase transition temperature decreases with Bi doping.

Doped crystals show only one phase transition between 135-155 K.

Lattice constant decreases as Bi is incorporated, confirming strain effects.

Abstract

We study the effects of bismuth doping on the crystal structure and phase transitions in single crystals of the perovskite semiconductor methylammonium lead tribromide, MAPbBr3. By measuring temperature-dependent specific heat capacity (Cp) we find that, as Bi doping increases, the phase transition assigned to the cubic to tetragonal phase boundary decreases in temperature. Furthermore, after doping we observe one phase transition between 135 and 155 K, in contrast to two transitions observed in the undoped single crystal. These results appear strikingly similar to previously reported effects of mechanical pressure on perovskite crystal structure. Using X-ray diffraction, we show that the lattice constant decreases as Bi is incorporated into the crystal, as predicted by density functional theory (DFT). We propose that bismuth substitutional doping on the lead site is dominant, resulting in BiPb+ centers which induce compressive chemical strain that alters the crystalline phase transitions.