Synthesis and Dielectric Properties of Layer-structured Compounds A_n−3Bi₄Ti_nO_3n+3 (A = Ba, Sr, Ca) with n > 4

Several bismuth layer-structured compounds A_n−3Bi₄Ti_nO_3n+3 (A = Ba, Sr, Ca) with n > 4 were synthesized and investigated. The average radius of A-site cations was found to be closely related to the lattice parameters in the a–b plane and, therefore, closely related to the stability of the layer structure. For Ba₂Bi₄Ti₅O₁₈ ceramics, there was a diffused phase transition centered at approximately 330 °C, which should be due to the cation redistribution of A-site Ba²⁺ and Bi³⁺ in the (Bi₂O₂)²⁺ layer. For Sr₂Bi₄Ti₅O₁₈ ceramics, a sharp dielectric constant peak was found at 325 °C. Ceramics of five-layered Ca₂Bi₄Ti₅O₁₈ and six-layered Ca₃Bi₄Ti₆O₂₁ showed temperature-stable dielectric constants up to 800 °C, and ferroelectricity was observed. In addition, as ferroelectrics, these Ca-containing bismuth layer-structured compounds showed frequency-independent dielectric constants >150 and small tan δ on the order of 10⁻³–10⁻⁴ in the frequency range of 1 kHz to 1 MHz.