The crystal structure of the CH3NH3PbBr3perovskite has been investigated under high-pressure
conditions
by synchrotron-based powder X-ray diffraction. We found that after
the previously reported phase transitions in CH3NH3PbBr3(Pm3̅m→Im3̅→Pmn21), which occur below 2 GPa, there is a third transition to
a crystalline phase at 4.6 GPa. This transition is reported here for
the first time contradicting previous studies, which reported amorphization
of CH3NH3PbBr3between 2.3 and 4.6
GPa. Our X-ray diffraction measurements show that CH3NH3PbBr3remains crystalline up to at least 7.6 GPa,
the highest pressure covered by experiments. The new high-pressure
phase is also described by the space groupPmn21; however, the transition involves abrupt changes in the unit-cell
parameters and a 3% decrease of the unit-cell volume. Our conclusions
are confirmed by optical-absorption experiments, by visual observations,
and by the fact that pressure-induced changes up to 10 GPa are reversible.
The optical studies also allow for the determination of the pressure
dependence of the band-gap energy, which is discussed using the structural
information obtained from X-ray diffraction.