Atomic-scale control of TiO₆ octahedra through solution chemistry towards giant dielectric response

The structures of many important functional oxides contain networks of metal-oxygen polyhedral unitsi.e. MO_n. The correlation between the configurations and connectivities of these MO_n to properties is essentially important to be well established to conduct the design, synthesis and application of new MO_n-based functional materials. In this paper, we report on an atomic-scale solution-chemistry approach that for the first time enables TiO₆ octahedral network control starting from metastable brookite TiO₂ through simultaneously tuning pH values and interfering ions (Fe³⁺, Sc³⁺, and Sm³⁺). The relationship between solution chemistry and the resultant configuration/connectivity of TiO₆ octahedra in TiO₂ and lepidocrocite titanate is mapped out. Apart from differing crystalline phases and morphologies, atomic-scale TiO₆ octahedral control also endows numerous defect dipoles for giant dielectric responses. The structural and property evolutions are well interpreted by the associated H+/OH^- species in solution and/or defect states associated with Fe³⁺ occupation within TiO₆ octahedra. This work therefore provides fundamental new insights into controlling TiO₆ octahedral arrangement essential for atomic-scale structure-property design.