Mineral-Inspired Oxides: Synthesis and Structure, Luminescence, and Electrocatalytic Studies.

Abstract

Transition-metal oxides (TMOs) and mineral-inspired oxides have emerged as versatile materials owing to their rich structural diversity and tunable physical properties. A broad class of oxide materials such as those adopting spinel, wolframite, perovskite, garnet, and pyrochlore-type structures, exhibit exceptional structural flexibility, allowing for tuning of their physical and chemical properties through strategic elemental substitutions within their frameworks.However, one of the main challenges lies in the controlled synthesis and stabilization of these under laboratory conditions, which opens up opportunities for discovering novel structures and functionalities.

This study focuses on the design, synthesis, and structure–property relationships of transition-metal oxides and mineral-inspired oxides for multifunctional applications. By employing targeted cation substitution and site engineering, we have successfully modulated optical properties (UV-cutoff materials, near-infrared (NIR) reflectors), achieving tunable color (pigments), magnetic behavior, dielectric characteristics, and nonlinear optical properties such as second-harmonic generation (SHG). Additionally, their photoluminescence, photocatalytic, and electrocatalytic activities were examined, with particular emphasis on their applicability in energy and optical technologies.

We have investigated LiZnNbO₄-based inverse spinel oxides as potential hosts for color-tunable compounds and as candidates for nonlinear optical materials, particularly focusing on their second-harmonic generation (SHG) response. We have also investigated a newly synthesized analogue of the Burckhardtite mineral, PbTeGa[AlSi3O8]O6 under laboratory conditions, with a focus on its red luminescence properties and magnetic behavior. In addition, we have explored structurally diverse mineral-based frameworks, such as Milarite-type compounds, Na2Mg5-xMxSi12O30 (M = Co2+, Zn2+, Ni2+, Cu2+), Na2Mg2.5Ca0.5-xLaxZn2Si12O30 (La = Eu3+, Tm3+, Tb3+), where targeted cation substitutions yield bifunctional behavior, including tunable white-light luminescence and electrocatalytic activity toward water oxidation (OER). Furthermore, we have synthesized a series of double wolframite-type compounds with the general formula (AA’)(BB’)O8; A = Zn2+, Mg2+, Co2+, Ni2+, Cu2+, A’ = Fe3+, Ga3+, In3+, Mn3+, Sc3+, B = Nb5+, Ta5+, and B’ = W6+), and investigated their potential as new colored compounds arising from metal-to-metal charge transfer (MMCT) and correlated structural features and electrocatalytic functional applications. Additionally, the newly developed PbZn4SiTeO10 compound was explored as a red-emitting phosphor and as a promising material for electrocatalytic water oxidation (OER).