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Tuning the Microstructure of γ‑Ba4Nb2O9 Polymorph Prepared from Single-Molecular Precursor

Although γ-Ba4Nb2O9 was considered to be metastable at room temperature (RT) and, therefore, prepared only by quenching from high temperatures, a new procedure for preparation of pure γ-Ba4Nb2O9 from a single- molecular precursor, the oxalate-based complex {; ; ; ; Ba2(H2O)5[NbO(C2O4)3]- HC2O4}; ; ; ; ·H2O, is described. This study focuses on controlling the phase composition and the crystallite domain lengths by altering preparation conditions, namely, (i) the time for which samples were held at the given temperature and (ii) the cooling rate. The high-temperature γ-Ba4Nb2O9 polymorph has been successfully retained and stabilized at RT ; the desired crystallite size in the nanoscale regime, ranging from ∼5 to 20 nm, can easily be tuned. The crystallite domain length and lattice strain were calculated from X-ray diffraction line-broadening analysis performed during Rietveld structure refinement.

metal oxides; crystallite size; Rietveld refinement; XRD

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