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Abstract
Devonshire's potential for description of the successive phase transition in BaTiO3 has been considered in the light of the catastrophe theory. The general perturbation to triple butterfly x 6 + y 6 + z 6 is expressed by 124 unfolding terms. The unfolding coefficients are diffeomorphically mapped to field variables of the same number. Cubic symmetry reduces this to 9. Devonshire's potential is a result of a physical simplification retaining only one field variable: temperature. Addition of symmetry-breaking terms for external fields in three directions enables us to calculate many physical properties of BaTiO3. Phase diagram in temperature-external field space has been given. In connection to this, triple hysteresis loops near tetragonal-orthorhombic and orthorhombic-rhombohedral transitions are expected from calculations, besides the well-known double hysteresis loop just above cubic-tetragonal transition.