Effects of sample preparation on the mechanical properties of AlMgB14

Using synchrotron-based x-ray diffraction we have studied the behaviour of two different preparations of the super hard material AlMgB14 at pressures up to 41GPa. Analysis of lattice parameter data from the high-pressure x-ray measurements provides a bulk modulus (K) of 196GPa and a pressure derivative of the bulk modulus (K') of 4.2 for sample 1, which was prepared by comminuting the elements and then hot pressing the sample. For sample 2, which was prepared by comminuting the elements and then cold pressing, K=264GPa and K'=3.7. The differences in K and K' clearly demonstrate that sample preparation significantly affects the mechanical properties of AlMgB14.