Abstract
Perovskite-type oxynitrides hold great potential for optical applications due to their excellent visible light absorption properties. However, only a limited number of such oxynitrides with modulated physical properties are available to date and therefore alternative fabrication strategies are needed to be developed. Here, we introduce such an alternative strategy involving a precursor microstructure controlled ammonolysis. This leads to the perovskite family member LaTa(IV)O2N containing unusual Ta4+ cations. The adjusted precursor microstructures as well as the ammonia concentration are the key parameters to precisely control the oxidation state and O:N ratio in LaTa(O,N)3. LaTa(IV)O2N has a bright red colour, an optical bandgap of 1.9 eV and a low (optically active) defect concentration. These unique characteristics make this material suitable for visible light-driven applications and the identified key parameters will set the terms for the targeted development of further promising perovskite family members.
Highlights
In this in situ and ex situ experimental study, we override the above-mentioned strong topotactic relation between oxide precursor and resulting LaTa(O,N)[3] formation through a considered selection of well-characterised oxide precursors with different microstructures and an adjusted ammonia concentration
We demonstrate the formation of the LaTa(IV)O2N utilising nanocrystalline lanthanum tantalum oxide (n-LTO), which exhibits smaller primary particles and a higher specific surface area than microcrystalline LaTaO4 (m-LaTaO4)
Nanocrystalline lanthanum tantalum oxide (n-LTO) and microcrystalline LaTaO4 (m-LaTaO4) were synthesised as precursors in order to investigate the effect of the microstructure on the reaction behaviour
Summary
In this in situ and ex situ experimental study, we override the above-mentioned strong topotactic relation between oxide precursor and resulting LaTa(O,N)[3] formation through a considered selection of well-characterised oxide precursors with different microstructures and an adjusted ammonia concentration. We demonstrate the formation of the LaTa(IV)O2N utilising nanocrystalline lanthanum tantalum oxide (n-LTO), which exhibits smaller primary particles (nm-range) and a higher specific surface area than microcrystalline LaTaO4 (m-LaTaO4). This adjusted precursor microstructure leads to a favoured Ta reduction in n-LTO. Ammonolysis of larger primary particles in the μm-range (m-LaTaO4) results in conventional LaTa(V)ON2. We expand the experimental toolbox by an additional method to access further requested perovskite-type oxynitride family members
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