Pressure dependence of the refractive index of diamond, cubic silicon carbide and cubic boron nitride

The pressure dependence of the refractive index of diamond, cubic boron nitride and cubic silicon carbide, was measured up to 9 GPa by an interferometric method using the diamond anvil cell. A least-square fit yields the following values for (1/n) (dn/dP): -3.6 x 10(-4) GPa(-1) for diamond, -3.2 x 10(-4) GPa(-1) for c-BN and, for 3C-SiC, -8.3 x 10(-4) GPa(-1). These results were used to investigate, for the first time under pressure, general empirical relationships between refractive index and energy gap found in the literature. The volume dependence of the electronic polarizability, alpha, of these compounds was determined through the Lorentz-Lorenz approach. The obtained linear behavior of alpha for the three cases was correlated to previous results for the pressure dependence of the transverse effective charge, e*(T). Copyright (C) 1996 Elsevier Science Ltd