Pressure response of an organic-inorganic perovskite: Methylammonium lead bromide

The behavior of the organic - inorganic perovskite, methylammonium lead bromide, as a function of pressure was studied up to pressures slightly above 3 GPa at temperatures between ambient and ∼80 K using neutron diffraction. The sample transforms from Pm3̄m to Im3̄ just below 1 GPa and amorphizes around 2.8 GPa without the cations undergoing long-range orientational ordering. The response of the orientationally ordered Pnma phase to pressure, which could not be accessed experimentally, was studied with density functional theory methods. The major source of volume reduction under compression is by tilting, and to a lesser extent shrinking, of the PbBr₆ octahedra.