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 boro n nitride and cubic silicon carbide, was measured up to 9 GPa by an in terferometric 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) f or 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 tim e under pressure, general empirical relationships between refractive i ndex and energy gap found in the literature. The volume dependence of the electronic polarizability, alpha, of these compounds was determine d 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). Copyrig ht (C) 1996 Elsevier Science Ltd