Effect of pressure on the superconducting transition temperature of   doped and neutron-damaged MgB2
  Measurements of the superconducting transition temperatures for Al-doped, C-doped and neutron-damaged-annealed MgB2 samples under pressure up to ~8 kbar are presented. The dT_c/dP values change systematically with the decrease of the ambient pressure T_c in a regular fashion. The evolution of the pressure derivatives can be understood assuming that the change in phonon spectrum is a dominant contribution to dT_c/dP. 
S. L. Bud'ko, R. H. T. Wilke, M. Angst, and P. C. Canfield