Phenomenologically derived electric field-temperature phase diagrams and piezoelectric coefficients for single crystal barium titanate under fields along different axes

The possible domain states of perovskite ferroelectrics under applied field s are reviewed and, as an illustration, a phenomenological study of barium titanate is carried out. Electric field-temperature phase diagrams, the pol arization, and the lattice strain of barium titanate single crystals are ca lculated from the Landau-Ginzburg-Devonshire theory of ferroelectrics for a pplied fields up to 20 MV m(-1) and for temperatures from 1 to 450 K. The c alculations are carried out for fields applied along the pseudocubic [001], [101], and [111] axes, revealing the temperature and field dependence of a ll the ferroelectric phase transitions. Large piezoelectric coefficients ca n be identified close to field-induced transitions. Good agreement is seen with experimental data for the piezoelectric coefficient parallel to [001] over a wide range of temperature. The series of transitions predicted for i ncreasing field parallel to [111] at room temperature is qualitatively simi lar to that observed experimentally but with somewhat larger critical field s and lower piezoelectric coefficients. Similarities are noted between the phase diagrams for fields along [001] and [111] and those describing Pb-Ba( 2+) and Zr-Ti(4+) substitutions. (C) 2001 American Institute of Physics.