The mechanical properties of Cdx Hg1-x Te

Cole, Simon (1982) The mechanical properties of Cdx Hg1-x Te. University of Southampton, Doctoral Thesis.

Abstract

The mechanical properties of Cdx Hgl_x To and BgTe have been investigated using microhardness, compression and bond testing techniques. The Vickers hardness, Hv, of Cdx Hgl-x To alloys has been measured as a function of composition, from x = 0 to 0.6, and at x e 1.0, at 25°C in darkness, on single crystal orlarge grained polycrystalline samples. H rises with increasing x from 26 kg.mm2 for vHgTe to n. 70 kgg mm 2 for x a 0.6, and drops to 50 kg.mm-2 for CdTO. Hv for C x Hg 1rx To (x - 0.2) is very low at 37 kq.mm 2, comparable with pure Al. The dependence of It v onx indicates that a maximum must occur somewhere in the range 0.6 < x < 1.0. This peaked form of curve is attributed to solid solution hardening, and the results are discussed in terms of likely hardening mechanisms in Cdx Hql-x To. The data show a deviation from ideal behaviour In the region x % 0.2, and a possible model for this is proposed. Compression tests have been conducted on HgTe single crystals at strain rate ~ 10-3sec 7l and temperatures between -60 and 25°C. At 25°C, plastic flow begins at stresses< I kg.mm 2. Single crystals of HgTe and Cdr Bgl-x To (0.10 < x < 0.3), oriented for single slip, have been deformed in four point bending at strain rates 'u 10 4 sec-1 and temperatures from -11 to a4°C for BgTe and 20 to 195°C for ^.!x Hg 1-x Te. At the lowest temperature, the stress-strain curve exhibits a sharp yield relaxation and subsequent easy glide regime, as commonly observed for other semiconductors. Experiments show that the yielding mechanism is that proposed by Johnston and Gilman for LSF. A possible explanation for the easy glide phenomenon is suggested. The influence of composition, temperature and strain rate on the stress-strain behaviour are reported. At 20°C, the upper and lower yield stresses (tuy and tly) increase with increasing x in qualitative agreement with the hardness results. tly (at strain rate ti 10 4 sec 1, x = 0.2) varies with temperature T according to tly a exp (Q/kT) with Q : 0.16 eV. For HgTe the comparable value is 0.11 eV. At x - 0.25, and constant temperature tly depends on strain rate r as Tly a y1/a with n o 4. The stress level for deformation of C x 0g 1-x To N 0.2) at y % 1D-4 see-1 and 20°Cis 2-3 kg.mm2, comparable with InSb at 300°C or Si at 1000°C. Cdx Hgl-x To may deform at temperatures below 25°C at these strain rates. Possible consequences of these findings are discussed. Strain rate cycling tests on Cdx Hgl-x To give values of activation volume Vt around 10b3 at 'I. 20°C, independent of plastic strain, sugjesting that deformation in these alloys is governed by the Peierls mechanism, as observed in other 11 - VI compounds.

This record has no associated files available for download.

Contributors

Download statistics