  BaFe2Se3 is a potential superconductor material exhibiting transition at 11 K
and ambient pressure. Here we extended the structural and performed electrical
resistivity measurements on this compound up to 51 GPa and 20 GPa,
respectively, in order to distinguish if the superconductivity in this sample
is intrinsic to the BaFe2Se3 phase or if it is originating from minor FeSe
impurities that show a similar superconductive transition temperature. The
electrical resistance measurements as a function of pressure show that at 5 GPa
the superconducting transition is observed at around 10 K, similar to the one
previously observed for this sample at ambient pressure. This indicates that
the superconductivity in this sample is intrinsic to the BaFe2Se3 phase and not
to FeSe with Tc > 20 K at these pressures. Further increase in pressure
suppressed the superconductive signal and the sample remained in an insulating
state up to the maximum achieved pressure of 20 GPa. Single-crystal and powder
X-ray diffraction measurements revealed two structural transformations in
BaFe2Se3: a second order transition above 3.5 GPa from Pnma (CsAg2I3-type
structure) to Cmcm (CsCu2Cl3-type structure) and a first order transformation
at 16.6 GPa. Here, {\gamma}-BaFe2Se3 transforms into {\delta}-BaFe2Se3 (Cmcm,
CsCu2Cl3-type average structure) via a first order phase transition mechanism.
This transitions is characterized by a significant shortening of the b lattice
parameter of {\gamma}-BaFe2Se3 (17%) and accompanied by an anisotropic
expansion in the orthogonal ac plane at the transition point.
