Abstract
This work investigates the high-pressure structure of freestanding superconducting (T-c = 4.3 K) boron-doped diamond (BDD) and how it affects the electronic and vibrational properties using Raman spectroscopy and x-ray diffraction in the 0-30 GPa range. High-pressure Raman scattering experiments revealed an abrupt change in the linear pressure coefficients, and the grain boundary components undergo an irreversible phase change at 14 GPa. We show that the blueshift in the pressure-dependent vibrational modes correlates with the negative pressure coefficient of T-c in BDD. The analysis of x-ray diffraction data determines the equation of state of the BDD film, revealing a high bulk modulus of B-0 = 510 +/- 28 GPa. The comparative analysis of high-pressure data clarified that the sp(2) carbons in the grain boundaries transform into hexagonal diamond.