Coordination clusters with octahedral geometry as a basis for highly ordered mixed-metal oxide layers with pronounced memristive properties

• Applicants: Dr. Jürgen W. Gerlach; Dr. Kirill Monakhov
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation ; Solid State and Surface Chemistry, Material Synthesis
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 537270815

Oxide layers of transition metals play a central role in the fabrication of memristive data storage devices, in which changes of the electrical conductance (e.g. by local valence changes of metal centers) induced by externally applied potentials are used to store information. These storage devices are characterized by high energy efficiency, scalability, and durability, which makes them a promising alternative to common charge-based storage devices in many areas. Mixed metal oxides, which are usually generated by using common sputtering, PLD, or ALD processes, are also increasingly being investigated to optimize the switching properties. Apart from the high energy consumption of these high-temperature processes, there is often an inhomogeneous distribution of the different types of metals and their oxide phases in the as-formed layers. Within the framework of the "House-of-Oxides" project, we present an alternative route to such technically interesting, multimetallic oxide films, which is based on the thermally or photochemically induced transformation of organically functionalized, hexanuclear transition metal-oxo clusters as neutral congeners of anionic Lindqvist-type polyoxometalates. For this purpose, Zr6- and Ce6-oxo clusters will first be synthesized as precursors with various 3d, 4f, alkali and/or alkaline earth metals and deposited on various metallic and nonmetallic surfaces. The well-defined stoichiometry of produced polynuclear coordination compounds is assumed to ensure optimal mixing of different metal centers. The organic ligands of these precursors will then be removed by thermal treatment or irradiation with energetic photons, so that phase-pure mixed metal-oxide layers will be formed. Both the synthesis and the oxide formation are low-temperature processes (up to a maximum of 300°C), which are characterized by a significantly improved energy balance compared to conventional processes, usually taking place in a temperature range from 800 to 1200°C. The choice of zirconium and cerium-based oxo-clusters over the technically more common hafnium and titanium was made because of the higher stability of the oxide phases with comparable switching properties and price advantages. In principle, however, it is also possible to transfer the methodology to complexes with the latter metals because of their chemical similarity.

• DFG Programme: Research Grants