Dielectric properties in A-site substitution type relaxor ferroelectric perovskite titanates Ba1-x(La0.5Na0.5)xTiO3

In order to investigate the effect of A-site substitution on phase transitions in barium titanates, dielectric permittivity in Ba1-x(La0.5Na0.5)xTiO3 was measured in the temperature range up to 400 K with frequency of 100 Hz to 100 kHz by changing x from 1/8 to 4/8. The transition from classical non-relaxor ferroelectric (x=1/8) to relaxor ferroelectric (x≥3/8) occurs, through the intermediate between classical non-relaxor and relaxor ferroelectrics (x=2/8). There is a strong correlation between the ionic mass at the A site M and the temperature of the permittivity maximum. It is found that M is one of the important parameters which dominates the dielectric permittivity and phase transitions in perovskite titanates. The diffusive displacement of Ti4+ due to the random fields created by inhomogeneity which A-site substitution introduces, besides the displacement suppressed by the shrinkage of lattice constant, reduces the permittivity maximum when x≥3/8. (author)