Advanced Structural Characterization of BaSn(OH)₃(OOH)(OO) Nanoclusters and BaSnO₃ Nanoparticles

Barium stannate (BaSnO₃) is a cubic perovskite with n-type semiconductor characteristics, high optical transparency and electronic mobility, which is used as an essential component of optoelectronic devices such as solar cells or gas detectors.^1–3 The synthesis and proper crystallization of the perovskite phase requires harsh conditions, such as elevated temperature (>1000 °C), pressure, or are time consuming, which normally result in samples with low control of the particle’s size distribution, stoichiometric and crystallinity.^2–4 A low-temperature synthesis route of BaSnO3 nanoparticles has been reported and can overcome those problems of classical synthesis approaches.¹ A crystalline molecular cluster identified as BaSn(OH)₃(OOH)(OO) can be obtained by basic precipitation in a concentrated hydrogen peroxide solution.^1,5 This cluster has cubic structure with replacement of the oxygen atoms of the classical perovskite structure by (OH)^-, (OOH)^- and (OO)^- groups, and can also be converted to the desired BaSnO₃ perovskite phase upon heating at temperatures as low as 300 °C.^1,5 When the molecular cluster is thermally treated it loses ~18% of its total mass by releasing H₂O and O₂ from the decomposition of the (OH)^-_, (OOH)^- and (OO)^- groups which causes a decrease in the parameters of the cubic network due to the contraction of the cell.^1,5 We treated this molecular cluster in vacuum at different temperatures (200-800 °C) and performed structural analyzes of the obtained materials by X-ray Diffraction (XRD) and transmission electron microscopy techniques such as Pair Distribution Function from Electron Diffraction (e-PDF).⁶ Our data indicate that the crystalline molecular cluster presents amorphous features with short-range order radius of 1.3 nm. All heat-treated samples resulted in the formation of perovskite BaSnO₃ nanoparticles, including the one treated at 200°C, and have short-range order radius of 2.0 nm (200 °C), 2.7 nm (400 °C), 3.6 nm (600 °C) and 4.6 nm (800 °C).

Acknowledgements:
FAPESP Grant Nos. 2023/00906-1 and 2013/07296-2

References:
1. Shin, S. S. et al. Colloidally prepared La-doped BaSnO ₃ electrodes for efficient, photostable perovskite solar cells. Science (1979) 356, 167–171 (2017).
2. Lee, W.-J. et al. Transparent Perovskite Barium Stannate with High Electron Mobility and Thermal Stability. Annu Rev Mater Res 47, 391–423 (2017).
3. Marikutsa, A. et al. Improved H2S sensitivity of nanosized BaSnO3 obtained by hydrogen peroxide assisted sol-gel processing. J Alloys Compd 944, (2023).
4. Azad, A.-M. & Hon, N. C. Characterization of BaSnO3-based ceramics. J Alloys Compd 270, 95–106 (1998).
5. Medvedev, A. G. et al. Identification of Barium Hydroxo-Hydroperoxostannate Precursor for Low-Temperature Formation of Perovskite Barium Stannate. Inorg Chem 59, 18358–18365 (2020).
6. Souza Junior, J. B. et al. Pair Distribution Function Obtained from Electron Diffraction: An Advanced Real-Space Structural Characterization Tool. Matter 4, 441–460 (2021).