X-ray diffraction and Raman spectroscopic study of nanocrystalline CuO under pressures

Compressibility of an oxide does not necessarily change due to decrease in particle size. This is found in nanocrystalline CuO, an important semiconductor. We studied nanometric CuO with high energy synchrotron radiation and Raman spectroscopic techniques to pressures of 47 GPa. Our results indicate that nanometric CuO has the same bulk modulus as observed in the macrometric CuO. Combination of results obtained from MgO, Ni, and ε-Fe indicates that the contribution of the size-induced surface energy to total internal energy has very little effect on the high pressure behavior of this type of nanomaterials, in which their bulk counterparts exhibit the structural stability over a wide range of pressure. This result is contrary to some observations, showing that the reduction of particle size significantly leads to increased bulk modulus.