Bp. Burton et Re. Cohen, NONEMPIRICAL CALCULATION OF THE PB(SC0.5TA0.5)O-3-PBTIO3 QUASI-BINARYPHASE-DIAGRAM, Physical review. B, Condensed matter, 52(2), 1995, pp. 792-797
The nonempirical potential induced breathing (PIB) method has been use
d to calculate structural parameters and total energies for PbTiO3 (PT
), ten different ordered structures with stoichiometry Pb(Sc0.5Ta0.5)O
-3 (PST), and 104 different structures with stoichiometries between PS
T and PT. The PIB results for intermediate stoichiometries predict two
ordered ground-state phases at X(PbTiO3)=1/4 and X=1/2. The differenc
es in total energies were used as a basis for fitting a set of effecti
ve cluster interactions, and the resulting Hamiltonian was used as inp
ut for a cluster-variation method (CVM) phase diagram calculation. The
CVM calculation predicts a third ordered phase at X approximate to 1/
4. This phase is not a ground state, but it is predicted to be stable
at higher temperatures than either of the ground-state phases and, the
refore, to be more likely to be found experimentally.