Crystal structure and dielectric properties of La3+ substituted Ba5LaTi3Ta7O30 ceramics

The effects of La3+ partial substitution for Ba2+ on crystal structure and dielectric properties were investigated for modification of Ba5LaTi3Ta7O30 ceramics. When the substitution x > 0.6, the sintering temperature obviously decreased. Superstructure peaks were observed for more La3+ substitution (x  ≥  2.4). The stability of the tetragonal tungsten bronze phase was discussed with electronegativity difference and tolerance factor. Lattice parameters decreased at first, and then slightly increased; while axial ratio decreased with increasing La content. Dielectric constant slightly increased when x  <  1.2, then gradually declined with the increase of La substitutions for Ba. Dielectric loss was very low except x = 2.4. Temperature coefficient of dielectric constant (at 1 MHz) was remarkably improved. The variation of dielectric properties was discussed from the change of crystal structure as well as the effects of vacancies at A-sites and superstructure.