  Cubic boron phosphide BP has been studied in situ by X-ray diffraction and
Raman scattering up to 55 GPa at 300 K in a diamond anvil cell. The bulk
modulus of B0 = 174(2) GPa has been established, which is in excellent
agreement with our ab initio calculations. The data on Raman shift as a
function of pressure, combined with equation-of-state data, allowed us to
estimate the Gr\"uneisen parameters of the TO and LO modes of zinc-blende
structure, {\gamma}GTO = 1.16 and {\gamma}GLO = 1.04, just like in the case of
other AIIIBV diamond-like phases, for which {\gamma}GTO > {\gamma}GLO = 1. We
also established that the pressure dependence of the effective electro-optical
constant {\alpha} is responsible for a strong change in relative intensities of
the TO and LO modes from ITO/ILO ~0.25 at 0.1 MPa to ITO/ILO ~2.5 at 45 GPa,
for which we also find excellent agreement between experiment and theory.
