Melting of cubic boron phosphide, BP has been studied at pressures to 9 GPa using synchrotron X-ray diffraction and electrical resistivity measurements. It has been found that above 2.6 GPa BP melts congruently, and the melting curve exhibits negative slope -60(7) K/GPa, which is indicative of a higher density of the melt as compared to the solid phase.
@article{arxiv.1511.05995,
title = {On melting of boron phosphide under pressure},
author = {Vladimir L. Solozhenko and Vladimir A. Mukhanov},
journal= {arXiv preprint arXiv:1511.05995},
year = {2015}
}