| Popis: |
The β → α transformation in plutonium is discussed in terms of the crystallography of the two phases and the resulting topological modeling of the β/α interface. There has been little microscopy work on the transformation, but it is probably martensitic. β-Pu is monoclinic I 2/ m , while α-Pu is monoclinic P 2 1 / m . α-Pu has been described as a hexagonal close-packed pseudostructure with AB stacking of the (0 2 0) α planes with pseudo-close-packing along [1 0 0] α and two other directions. β-Pu is less obvious, but X-ray diffraction suggests that the (1 0 3) β planes, which are selected as the terrace plane, have the highest structure factor and are therefore among the closest-packed planes. Other pseudo-close-packed planes, such as { 2 2 2 ¯ } β and { 3 2 1 ¯ } β , could also act as terrace planes for the transformation. The (1 0 3) β planes have a pseudo-hexagonal grid of Pu atoms with AB stacking and pseudo-close-packing along [ 3 0 1 ¯ ] β and two other directions. A selection of terrace planes as (0 2 0) α //(1 0 3) β with disconnections along [ 1 0 0 ] α / / [ 3 0 1 ¯ ] β provides the basis for topological modeling. The model predicts a habit plane that is ∼6° from the terrace plane. The extra Pu atoms in the β structure (17 for every 16 in α) are accommodated by having 16 (1 0 3) β planes transform into 17 (0 2 0) α planes at steps in the interface. Short-range interstitial diffusion of Pu atoms from β to α is required for the transformation to proceed. Possible lattice invariant deformation systems are discussed. |
Full Text from ScienceDirect