Optical properties of α- and β-CuZn brasses in the region of quantum absorption

The optical constants n and k of CuZn brasses with Zn content of 39, 40, 41, 47, 50 at% (β-phase) and 35 at% (α-phase) are measured at 293 K, and with Zn content of 35, 39, and 50 at% at 78 K also, in the 1 to 0.25 μm spectral range by the polarimetric method. From n and k reflectance R(λ), high-frequency conductivity σ(ω) (where ω is the light wave cyclic frequency), the real and imaginary parts e1(ω) and e2(ω) of the complex dielectric constant, and the electron characteristic loss function e/e + e are derived. Their concentration and temperature dependences are analyzed. The different characters of the concentration and temperature dependences of the absorption edge of α- and β-brasses confirm that its origin in these alloys is not the same: in α-brasses the edge is formed by interband transitions from EF to vacant states of the conduction band, while in β-brasses by d-band to EF transitions. No substantial change in the optical interband absorption is observed in both, the concentration and temperature (martensitie) b.c.c. to f.c.c. transitions.