Reconstructive transitions between ordered phases: The martensitic fcc-hcp and the graphite-diamond transitions

Theoretical approach to reconstructive and morphotropic phase transitions

“…The HCP-FCC transition in these elements display a weakly first-order character excluding the possibility of large displacements that would be required in a Brought to you by | Monash University Library Authenticated Download Date | 6/3/15 4:55 PM displacive reconstructive mechanism. In contrast in the graphite-diamond transition, which is strongly first order, the reordering process between almost close-packed structures is coupled to displacements of the carbon atoms [3,18].…”

“…This is for example the case for the FCC-HCP transition which takes place in Co and He where the FCC and HCP phases are not adjacent to a parent BCC phase [18,19]. The HCP-FCC transition in these elements display a weakly first-order character excluding the possibility of large displacements that would be required in a Brought to you by | Monash University Library Authenticated Download Date | 6/3/15 4:55 PM displacive reconstructive mechanism.…”

“…[3,18,19]. However, the essential features of the corresponding approach are used in the description of morphotropic transitions, given in the following section.…”

Continuum theory of carbon phases

“…as a transition between two low-symmetry ordered phases, which are derived from a common disordered hexagonal latent parent phase''. It was also found in [38,39] that ''an essential parameter appears to be the degree of occupancy of the latent unit cell by the atoms (i.e., the concentration).'' The treatment in [38,39], however, did not produce a phase diagram of carbon as a real material, which should be accomplished by our model.…”

“…It was also found in [38,39] that ''an essential parameter appears to be the degree of occupancy of the latent unit cell by the atoms (i.e., the concentration).'' The treatment in [38,39], however, did not produce a phase diagram of carbon as a real material, which should be accomplished by our model. That is why we will be using an effective scalar structural OP n associated with the graphite-diamond transition, which describes the most favorable path between the graphite and diamond phases in the multi-dimensional space of the structural OP's.…”