Antiphase boundaries in GdDy(MoO4)3 crystals : evaluation of their thickness and energy from experimental results

By means of X-ray topographic methods it has been previously demonstrated [B. Capelle, C. Malgrange, J. Appl. Phys. 53 (1982) 6762] that the crystalline lattice was distorted in antiphase domain boundaries (APB) of GDMO crystals. The distortion gives a resultant translation vector between two adjacent antiphase domains whose component along b is negligible compared to the a component (≃ a/30). Barkley and Jeitschko [J. Appl. Phys. 44 (1973) 938] have shown that, in the same material, antiphase domain boundaries created behind moving ferroelectric domain walls have a common orientation which varies with the temperature at which they are created. The orientation of the APB's is shown here to result from a competition between the energy related to the order parameter and the elastic energy. In order to take into account the elastic energy, a simplified model of the antiphase domain boundary is proposed. The other part of the energy is considered by means of Fousek's and Fouskova's treatment [Phys. Status Solidi (a) 32 (1975) 213]. The adjustment between experimental results and theoretical parameters allows to determine the thickness of the APB (about 100 Å at room temperature) and the value of the « stiffness » coefficient entering in the free energy of the APB.