FOR 5044:  Periodic low-dimensional defect structures in polar oxides

• Subject Area: Materials Science and Engineering ; Physics
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 426703838

Polar oxidic lithium niobate-lithium tantalate solid solutions (LNT) represent an extraordinarily variable model system for the disclosure and application of new fundamental materials and physical phenomena due to their miscibility over the entire compositional range and the tunable size of ferroelectric domains. The impact of point defects and domain walls on macroscopic material properties, their interaction and high thermal stability provide a novel and broad range of emerging applications for piezoelectric structures such as actuators and acoustic crystals, but equally for nanoelectronic and nonlinear and optoelectronic applications up to high temperatures. In particular, we anticipate that the intended adjustment of stoichiometry and domain structure allows to tailor the crystal properties and, for example, to take advantage of the high piezoelectric coefficients and the expected high domain wall conductivity.The objectives of the research group include the determination, understanding and correlation of defect structures, electronic and atomic transport and acoustic losses in polar oxides over a wide temperature range, especially at high temperatures. Initially, the understanding of point defects in monodomain crystals of different stoichiometry will be established, so that subsequently new insights into the impact of domain walls on point defects, atomistic transport and macroscopic crystal properties can be achieved. The main focus is on material science and physics issues, which include the identification of defects such as polarons and the transport of charge carriers in low-dimensional regions. Our results might have a larger impact to other material systems as well, which opens a bright perspective for future project phases. Within our preliminary work, LNT crystals were prepared by Czochralski growth and characterized in terms of their electrical properties. Furthermore, poling of crystals was demonstrated and the domain structure was visualized.The scientists involved provide complementary competences, ranging from crystal growth (TP1) over ion-transport investigation (TP2, TP3) and polaron dynamics (TP4, Mercator Module) to domain and domain-wall structure (TP5, TP6), electromechanical properties (TP7) and advanced modelling (TP8). This guarantees added benefit into this novel research field, which would not be possible without the present consortium. This leads to synergy, which is the precondition for the realization of the research concept. Simultaneously, two junior research groups will be established and the education of highly qualified PhD students and undergraduates is supported sustainably.

• DFG Programme: Research Units
• International Connection: Hungary

Projects

• Acoustic loss and electromechanical properties of LiNb_(1-x)Ta_xO_3 (Applicant Fritze, Holger )
• Control of non-linear self-localization phenomena of strongly coupling charge carriers in LiNb_(1-x)Ta_xO_3 (LNT) - solid solutions (Applicant Imlau, Mirco )
• Coordination Funds (Applicant Fritze, Holger )
• Crystal Growth and Basic Properties of Lithium Niobate - Lithium Tantalate Solid Solution Crystals (Applicant Ganschow, Steffen )
• Domain Walls in LNT Mixed Crystals (Applicant Eng, Lukas M. )
• Ion transport and point defects in LiNb_(1-x)Ta_xO_3 solid solutions (Applicants Fritze, Holger ;  Schmidt, Harald )
• Modeling ferroelectric LiNb_(1-x)Ta_xO_3 solid solutions and their defect structure (Applicant Sanna, Simone )
• Tailored domain structures in LiNb_(1-x)Ta_xO_3 solid solutions (Applicant Ruesing, Michael )
• Thermal Stability and Application Limits of LiNb_(1-x)Ta_xO_3 solid solutions (Applicant Suhak, Yuriy )

• Spokesperson: Professor Dr.-Ing. Holger Fritze