On the mechanism of the olivine-spinel phase transformation

Recent experiments on the olivine-spinel phase transformation in Ni₂SiO₄ have provided the following fundamental results: (1) the interphase structural orientation relationships with $\text{(100)}{}_{\mathrm{<mtext>ol</mtext>}}\text{|(111)}{}_{\mathrm{<mtext>sp</mtext>}}\text{and}\text{001]}{}_{\mathrm{<mtext>ol</mtext>}}\text{|}\text{1}\text{10]}{}_{\mathrm{<mtext>sp</mtext>}}$ between the olivine and spinel phases upon transformation; and (2) the growth of 300 μm spinel single crystal from single crystals of olivine. In the light of these observations, transformation mechanisms proposed have been compared. We conclude that neither a nucleation and growth model nor a martensite model is verified by the experimental results. The former model lacks consistency in terms of the interphase relationships, and the latter cannot offer a dislocation-multiplication mechanism for the growth process.