We wish to trace the changes in lattice parameters and atomic coordinates around the first and second order Curie transitions of Fe2P and boron (11B)-doped Fe2P0.95,B0.05 respectively. Our hope is to understand the origin of anisotropic exchange striction, metamagnetism and tricriticality in these materials, together with their extraordinary doping sensitivity. Fe2P is the mother compound of a series of FeMnP-type hexagonal alloys that are much-studied for their large magnetocaloric effect (MCE). The MCE is the magnetic field-induced change of temperature of a material, and it is typically largest at a magnetic phase transition. By understanding the physics of Fe2P, we will learn why, by comparison FeMnP compounds have tunable volume changes, reduced short range order effects (which normally limit the MCE) and why their first order properties are relatively insensitive to doping.