The Effect of an Electric Field on the Transitions of Barium Titanate

A review is presented of the effects of electric fields on the ferroelectric phase transitions of barium titanate at 120°C and 5°C. The double hysteresis loop observed at the Curie point and the triple hysteresis loop and dielectric constant measured at the 5°C transition are examined in the light of Devonshire's thermodynamic theory of ferroelectricity in barium titanate. The data and various published experimental results are shown to agree with calculations based on the Devonshire free-energy function. The discrepancy between the coercive fields predicted by the theory and those actually observed is discussed.