  A polycrystalline sample of FeSe, which adopts the tetragonal PbO-type
structure (P4/nmm) at room temperature, has been prepared using solid state
reaction. We have investigated pressure-induced structural changes in
tetragonal FeSe at varying hydrostatic pressures up to 0.6 GPa in the
orthorhombic (T = 50 K) and tetragonal (T = 190 K) phases using high resolution
neutron powder diffraction. We report that the structure is quite compressible
with a Bulk modulus around 31 GPa to 33 GPa and that the pressure response is
anisotropic with a larger compressibility along the c-axis. Key bond angles of
the SeFe4 pyramids and FeSe4 tetrahedra are also determined as a function of
pressure.
