Synthesis of Aurivillius Phase CaBi₄Ti₄O₁₅ Doped with both La³⁺ and Mn³⁺ Cations: Crystal Structure and Dielectric Properties

Abstract

The four-layer Aurivillius CaBi₄Ti₄O₁₅ with introducing of La³⁺ on the A-site and Mn³⁺ on the B-site with the formula Ca_1-xBi_3+xLaTi_4-xMn_xO₁₅ (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) were synthesized by molten salt method using the mixture of sulfate salts K₂SO₄/Na₂SO₄ as the flux. XRD data confirmed the formation of single-phase Aurivillius with A2₁am orthorhombic structure for x = 0, 0.2, 0.4, and 0.6, whereas for x = 0.8 and 1, the impurity phases were observed. SEM analysis shows the anisotropic plate-like grains, which are a typical grain of Aurivillius phases. The cell volume decreases with increasing x, indicating a presence of mixed valences of Mn³⁺ and Mn⁴⁺. The dielectric constants increased with x, strongly correlated with the higher distortion of the structure, the 6s² lone pair electrons of Bi³⁺ cation increase. The presence of Mn³⁺ unpaired electrons results in the increase of dielectric loss as increasing x.

Keywords:
Aurivillius phase; molten salts; orthorhombic structure; dielectric properties