Generic influences of charged defects on the structure-property relationships of modified ferroelectric barium titanate and antiferroelectric sodium niobate

Structure-property relationships were investigated to reveal the generic influence of various substituents on ferroelectric (FE) BaTiO3 and antiferroelectric (AFE) NaNbO3. Simulations of defect distribution, using a preliminary cellular automaton (CA) model, were also carried out. Interrelationships between defect distributions and macroscopic properties are discussed.;Compositional modification of ferroelectric BaTiO3 was systematically investigated for four types of aliovalent substitutions. A generic influence of charged defects in breaking down the ferroelectric domains was demonstrated. Relaxor behavior was induced in all four types of modified ferroelectric BaTiO 3. It was shown that the induced relaxor behavior was related to the concentration of charged defects, more so than the substituent type.;La+3 (x) modified antiferroelectric NaNbO3 (NNL-x) was also systematically investigated for x ≤ 5. Emphasis was placed on the field-induced AFE-FE transition. La+3 modification was found to result in enhanced difficulties of the field-induced AFE-FE transition. With increasing La+3 concentration, it was found that higher fields were required to induce the ferroelectric state. In addition, La +3 substitution was found to have less impact on the dielectric properties of antiferroelectrics than ferroelectrics.;A preliminary two-dimensional cellular automaton model of defect distribution was proposed based on space charge neutrality considerations. It used only pairwise nearest-neighbor interactions and neglected the elastic effects associated with lattice distortions. Simulations demonstrated a general distribution pattern for charged defects. With increasing substituent concentration, more and larger defect clusters formed, which might be related with the formation of polar nanodomains in the modified ferroelectric BaTiO3. The influence of charged defects on field-induced AFE-FE transition was discussed in terms of elastic strain effects.