Mechanisms of Structure Transformations in Thallous Nitrate Crystals

S. W. Kennedy, J. H. Patterson
1965 Proceedings of the Royal Society A  
Plate 23] G eom etrical an d kin etic facto rs in polym orphic tran sfo rm atio n s of single cry stals of th allo u s n itra te have been in v estig ated b y o ptical a n d X -ra y m ethods. T he tran sfo rm a tio n s o rth o rhom bic ^ rhom b o h ed ral can proceed by tw o d istin c t m echanism s w ith different kinetics. T he slower kinetics are associated w ith a m echanism w hich m ain ta in s a definite o rie n ta tio n relation a n d causes fo rm atio n of p lates of th e new p h a s e
more » ... th e new p h a s e : it is closely sim ilar to m arten sitic tran sfo rm atio n in alloys. D islocation e tch p its can be pro d u ced a t th e interface. N ucleatio n rates for th e other, 're c o n stru c tiv e ', m echanism were p re d o m in a n tly tim e-d ep en d en t in superheating, a n d tem p eratu re -d e p e n d e n t in supercooling. N ucleation ap p ears to occur a t defects. A tra n sfo rm a tio n from o rthorhom bic to cubic can occur in good cry stals a t 126*5 °C an d proceeds b y a th ird , continuous m echanism , desp ite th e sim ilarity o f th e stable rhom bohed ral stru c tu re to th e cubic. I t ap p ears th a t th e choice of a tra n sfo rm a tio n m echanism can d epend on am o u n t of im perfection a n d can be q u ite sensitive to sm all changes in th e difference b etw een th e stru ctu res.
doi:10.1098/rspa.1965.0041 fatcat:7yuyrmjsnfdb3kxlafjpal63uu