Publication date: 10th April 2024
The drastic Effect of A-site non-stoichiometry on the Cation Diffusion and Core-Shell Formation in NBT-based Ceramics
Sophie Bauer a, Till Frömling a,b
a Technical University of Darmstadt, Department of Materials and Earth Science, Peter‑Grünberg‑Straße 2, 64287 Darmstadt, Germany, sophie.bauer@mr.tu-darmstadt.de
b Fraunhofer Research Institution for Materials Recycling and Resource Strategies (IWKS), Aschaffenburger Straße 121, 63457 Hanau, Germany
Since Bi2O3 tends to evaporate easily during the solid-state synthesis of Na0.5Bi0.5TiO3‑based (NBT-based) ceramics, it is extremely challenging to control the oxygen and bismuth vacancy formation, and consequently, the stoichiometry of the composition. [1] As the diffusion processes in NBT‑based ceramics strongly depend on the vacancy concentration, the addition of 0.1 % bismuth can supress the grain boundary diffusion coefficient by six orders of magnitude. [1] Therefore, different microstructures, each with distinct properties, emerge depending on the degree of bismuth deficiency and, consequently, the concentration of oxygen and bismuth vacancies. [1, 2] In the case of Na0.5Bi0.5TiO3‑SrTiO3 (NBT-ST), a homogeneous material can be synthesized by introducing a slight bismuth deficiency in the starting material, while bismuth enrichment results in a core-shell microstructure. [2, 3] As expected, both materials exhibit fundamentally different properties. Bi-enrichment causes an exceptionally high achievable strain in this ferroelectric material and a high energy density that can be stored, offering potential applications in actuators and high-energy capacitors. In contrast, Bi deficiency results in a seven times larger grain size and significantly higher conductivity.
This work sheds light on the possibilities of tailoring the microstructure, transport properties, and electromechanical properties of NBT-based materials. Understanding the diffusion mechanisms of cations in NBT-based ceramics is inevitably crucial in this context.
Sophie Bauer and Till Frömling gratefully acknowledge the financial support by the Deutsche Forschungsgemeinschaft (DFG; Grant No.: 471260201).
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