Epitaxial LiNb1-xTaxO3 Films

• Applicant: Dr. Jutta Schwarzkopf
• Subject Area: Synthesis and Properties of Functional Materials ; Experimental Condensed Matter Physics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 426703838

This subproject deals with the epitaxial growth of LiNbxTa1-xO3 (LNT) films using pulsed laser deposition (PLD) on oxide substrates. Compared to the corresponding bulk materials (3D), the properties of thin films can differ significantly due to the reduced dimensionality (2D) and interfaces and surfaces play a much more prominent role than in bulk materials. The introduction of mechanical strain through heteroepitaxy also offers new degrees of freedom to deliberately modify properties (strain engineering). The overall aim of this subproject is therefore the fundamental investigation of the growth process of homo- and heteroepitaxial LiNbxTa1-xO3 thin films over the entire composition range from x = 0 (LN) to x = 1 (LT) using PLD as well as the influence of the growth parameters on the structural, physical and chemical film properties. For this purpose, the growth conditions (temperature, oxygen partial pressure, target composition, target-substrate distance, laser fluence/frequency) must be optimized with regard to a stoichiometric film composition without foreign phases and high structural quality without rotational domains. This is facilitated by an innovative machine learning approach that takes into account the dependencies between the various process parameters and their influence on the film properties and shows a new way for the targeted optimization of film properties. In addition to the fundamental growth investigations, a further aim of this subproject is the controlled introduction of mechanical lattice strain through heteroepitaxial film growth on lattice mismatched substrates. In cooperation with the other subprojects, it will be investigated how the lattice mismatch and the Nb/Ta ratio affect the growth process, defect formation, phase and domain formation (on a nanoscopic scale with TP6) and the poling behavior (TP5). The influence of lattice strain and film thickness on electrical (TP7) and ionic (TP2) transport, thermal stability (TP3), optical (TP4, TP5), electromechanical and electroacoustic (TP7) properties will be analyzed which will facilitate a targeted modification. Numerical model calculations (TP8) will provide a fundamental understanding of phase and domain formation, phase transition and transport mechanisms.

• DFG Programme: Research Units
• Subproject of: FOR 5044: Periodic low-dimensional defect structures in polar oxides