Compound Energy Formalism (CEF)

If the atoms are sufficiently different in size, electronegativity or charge, they may prefer different types of sites in the lattice of crystalline solids. In some cases, a solute atom may even occupy interstitial sites between the normal lattice sites. All such phenomena are treated in Thermo‑Calc by the sublattice concept. The Compound Energy Formalism (CEF) has proved to be the most general formalism for many different types of solution phases. It is therefore by default applied to various solid solution phases in the Thermo‑Calc software package. CEF can also take ionic constraints (charged cation/anion species) into account. For a comprehensive description on the CEF, please see Hillert (2001), Frisk and Selleby (2001), Sundman and Ågren (1981).

Since the CEF is used by default, no special notation is needed in the phase definition, except for ionic phases, where type code I is given.

Examples of phase definitions in a setup-file using the CEF:

ENTER_PHASE SPINEL I, 4 1 2 2 4

     FE+2,FE+3; FE+2,FE+3,VA; FE+2,VA; O-2; N N

ENTER_PHASE SIGMA, 3 10 4 16

     AL,CO,CR,FE,NB; AL,CO,CR,FE,NB; AL,CO,CR,FE,NB; N N

ENTER_PHASE FCC_A1, 2 1 1

     CR,FE,MN; C,N,VA; N N

ENTER_PHASE BCC_A2, 2 1 3

     CR,FE,MN,VA; C,N,VA; N N