Barium and strontium titanium oxides are very similar in structure and behavior, and both are used as ceramic capacitors or other electronic components in radio frequency and memory device applications. Due to their similarities, these materials are often modeled similarly when determining their growth parameters and performance, implementing only slight alterations to the same model. But subtle differences in underlying structure can, in fact, have markedly larger implications on the performance of each material.
Research from Baker et al. studies the differences in the vacancy behaviors of these two materials when doped, which control their electrical properties. The authors use density functional theory calculations using state-of-the-art functionals to describe the atomic interactions, including the intrinsic electronic structure and charge localization, to determine the underlying differences in the behavior of metal vacancies. Combining these calculations with semiconductor physics models allows them to explore how these differences play out when the materials are doped.
The vacancy sites within the materials differ due to physical differences in the energies of the resulting broken bonds and due to the variability in their accessible processing conditions, as dictated by material considerations. To determine the resulting material properties, the authors simulated typical dopants interacting with these vacancies during processing using the updated model.
Observable fundamental differences in the defect behaviors between the two oxides resulted from the model, which shows large differences in the most common vacancy present even when the dopants behaved similarly. However, not all dopants of the same type behave similarly in the two materials, implying that treating the two oxides the same, as has been done in the past, can lead to incorrect models, resulting in lower quality materials if used to guide processing.
Source: “Mechanisms governing metal vacancy formation in BaTiO3 and SrTiO3,” by Jonathon N. Baker, Preston C. Bowes, Joshua S. Harris, and Douglas L. Irving, Journal of Applied Physics(2018). The article can be accessed at https://doi.org/10.1063/1.5044746.
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