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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 28: Focus Session: (Multi-)Ferroic States IV

KFM 28.6: Talk

Thursday, March 21, 2024, 17:05–17:25, EMH 225

Point Defects and Domain Walls in Soft Ferroelectric CsGeX3 (X = Cl, Br, I) — •Kristoffer Eggestad, Benjamin Albert Dobson Williamson, Dennis Gerhard Meier, and Sverre Magnus Selbach — Department for Materials Science and Engineering - NTNU

Conductive domain walls (DWs) hold promise for nanoscale, energy-efficient multi-level diodes and neuromorphic circuitry. In CsGeX3, caesium and halogen vacancies are intrinsic point defects that can induce electrons and holes, respectively. Controlling the formation and position of vacancies can in principle give switchable local n-type or p-type conductivity at DWs and enable new concepts for DW-based circuitry. This requires a material where mobile point defects of both positive and negative charge can accumulate at DWs. CsGeX3 is here chosen as our model system due to the possibility of having mobile caesium and halogen vacancies.

Using hybrid density functional theory (DFT) we investigate electronic structure and defect formation energies in bulk, showing highly mobile holes and free electrons, as well as relatively shallow defect levels. Moreover, a study on point defect mobility in bulk, reveals exceptionally mobile anion vacancies with migration barriers comparable to Li vacancies in the best solid-state electrolytes. Furthermore, we show that Y-type 71-degree DWs are the most stable and that they are extremely mobile, implying that polarisation can easily be switched. Finally, the possibility of reversible p- and n-type conductivity in DWs in CsGeX3 and other similar materials is discussed.

Keywords: DFT; Point Defects; Domain Walls; Halide perovskites