(103)(331) SLIP IN MOSI2

{103}[331] slip is found to be activated in MoSi2 single crystals by d eformation along [001] in uniaxial compression at 1000-degrees-C. The {103} slip plane has been determined by slip trace analysis. Observati ons by transmission electron microscopy reveal the presence of screw d islocations with a Burgers vector of 1/2[331]. However, 1/2[331] dislo cations of mixed character lying along the [010] direction are observe d to have decomposed into two other perfect dislocations by the energe tically favourable reaction 1/2[331]-->1/2[111]+[110]. The occurrence of such dislocation decomposition explains the difficulty of observing 1/2[331] dislocations in previous work. The 1/2[331] screw dislocatio ns have been examined by weak-beam dark-field microscopy but dissociat ion into three 1/6[331] collinear partials could not be detected.