The high-pressure behavior of the hexagonal superconductor was investigated by using in situ synchrotron radiation X-ray diffraction under pressures of up to 42.2GPa in a diamond anvil cell. An abrupt decrease of about 7% in the unit cell volume occurred in the range of 26.3 to 30.2GPa. A split in the Raman spectrum was also observed. The jump of the compression curve and Raman spectrum were attributed to an isostructural transition at a pressure of 30.2GPa.

Isostructural Transition of MgB2 Under High Pressure. L.L.Sun, T.Kikegawa, Q.Wu, Z.J.Zhan, W.K.Wang: Chinese Physics Letters, 2001, 18, 1401-3