T(Z) DIAGRAM AND OPTICAL-ENERGY GAP VALUES OF (AGIN)(2(1-Z))(CDIN2)(Z)TE-4 ALLOYS

The T(z) diagram of the system (AgIn)(2(1-z))(CdIn2)(z)Te-4 is obtained from X-ray diffraction and differential thermal analysis measurements. At higher temperatures, there is a single phase solid solution across the complete diagram, the phase changing from a disordered defect zincblende to a partially- disordered tetragonal symmetry in the vicinity of z = 0.9. This high-temperature phase shows a eutectoid reaction at z = 0.65 and T = 490 degrees C giving the two tetragonal terminal phases alpha, with space group I $($) over bar$$ 42d corresponding to AgInTe2, and gamma, with I4 $($) over bar$$ corresponding to CdIn2Te4. At lower temperatures, the fields alpha and gamma are separated by a relatively wide two-phase field (alpha + gamma) which extends over the range 0.53 < z < 0.94. Values of room temperature optical energy gap E(0) are determined from optical absorption measurements in the ranges of single phase behaviour and the form of the E(0) versus z data curve is discussed. The form of this T(z) diagram is compared with that of related systems in which the terminal compounds have similar structure but differ in space group.