TEMPERATURE COMPOSITION PHASE-DIAGRAM AND OPTICAL-ENERGY GAP VALUES OF CU-2(1-Z)CDZIN2TE4 ALLOYS

The temperature-composition phase diagram of the system Cu-2(1-z)CdzIn 2Te4 was obtained from X-ray diffraction and differential thermal anal ysis measurements. At higher temperatures, there is an apparent single phase solid solution across the complete diagram, but the phase chang es abruptly from a disordered defect zinc-blende to a partially disord ered tetragonal symmetry somewhere in the range 0.85<z<1.0. This high- temperature phase shows a eutectoid reaction at z=0.65 and T=230 degre es C giving the two tetragonal terminal phases: a, with space group 1 $($) over bar$$ 42d corresponding to CulnTe(2); and gamma, with space group 1 ($) over bar 4 corresponding to Cdln(2)Te(4). At lower tempera tures, the fields alpha and gamma are separated by a relatively wide t wo-phase field (alpha+gamma), which extends over the range 0.35<z<0.75 . The form of this T(z) diagram is compared with those of related syst ems in which the terminal compounds have similar structure but differ in space group. The values of room-temperature optical energy gap, E(0 ) were determined from optical absorption measurements in the ranges o f single-phase behaviour, E(0) showed a different linear variation wit h z in each range.