Isostructural Transition of MgB₂ Under High Pressure

The high-pressure behaviour of superconductor MgB₂ with hexagonal structure has been investigated by the in-situ synchrotron radiation x-ray diffraction method under pressures up to 42.2GPa in a diamond anvil cell. An abrupt decrease of about 7% in the unit cell volume of this material occurs in the pressure range of 26.3 to 30.2 GPa. A split of Raman spectrum was also observed. The jump of compression curve and Raman spectrum are ascribed to an isostructural transition in MgB₂ at the pressure of 30.2GPa.