Investigation of the hydrothermal crystallisation of the perovskite solid solution NaCe{sub 1−x}La{sub x}Ti{sub 2}O{sub 6} and its defect chemistry

• Published in: Journal of solid state chemistry Vol. 207
• Main Authors: Harunsani, Mohammad H., Woodward, David I., Peel, Martin D., Ashbrook, Sharon E., Walton, Richard I.
• Format: Journal Article
• Language: English
• Published: United States 15.11.2013
• Subjects: ABSORPTION SPECTROSCOPY; CERIUM; CERIUM IONS; CRYSTALLIZATION; DEUTERIUM; HYDROTHERMAL SYNTHESIS; INFRARED SPECTRA; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; NEUTRON DIFFRACTION; NMR SPECTRA; NUCLEAR MAGNETIC RESONANCE; OXIDATION; PARAMAGNETISM; PEROVSKITE; RAMAN SPECTROSCOPY; SODIUM 23; SOLID SOLUTIONS; TRIGONAL LATTICES; X RADIATION; X-RAY DIFFRACTION; X-RAY SPECTROSCOPY
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/J.JSSC.2013.09.015

Perovskites of nominal composition NaCe{sub 1−x}La{sub x}Ti{sub 2}O{sub 6} (0≤x≤1) crystallise directly under hydrothermal conditions at 240 °C. Raman spectroscopy shows distortion from the ideal cubic structure and Rietveld analysis of powder X-ray and neutron diffraction reveals that the materials represent a continuous series in rhombohedral space group R3-bar c. Ce L{sub III}-edge X-ray absorption near edge structure spectroscopy shows that while the majority of cerium is present as Ce{sup 3+} there is evidence for Ce{sup 4+}. The paramagnetic Ce{sup 3+} affects the chemical shift and line width of {sup 23}Na MAS NMR spectra, which also show with no evidence for A-site ordering. {sup 2}H MAS NMR of samples prepared in D{sub 2}O shows the inclusion of deuterium, which IR spectroscopy shows is most likely to be as D{sub 2}O. The deuterium content is highest for the cerium-rich materials, consistent with oxidation of some cerium to Ce{sup 4+} to provide charge balance of A-site water. - Graphical abstract: A multi-element A-site perovskite crystallises directly from aqueous, basic solutions at 240 °C; while the paramagnetic effect of Ce{sup 3+} on the {sup 23}Na NMR shows a homogeneous solid-solution, the incorporation of A-site water is also found from {sup 2}H NMR and IR, with oxidation of some cerium to charge balance proved by XANES spectroscopy. Display Omitted - Highlights: • Direct hydrothermal synthesis allows crystallisation of a perovskite solid-solution. • XANES spectroscopy shows some oxidation of Ce{sup 3+} to Ce{sup 4+}. • The paramagnetism of Ce{sup 3+} shifts and broadens the {sup 23}Na solid-state NMR. • The perovskite materials incorporate water as an A-site defect.