Journal
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
Volume 103, Issue 11, Pages 6280-6288Publisher
WILEY
DOI: 10.1111/jace.17339
Keywords
cerium; cerium compounds; nanostructures; pigment; rare earths
Categories
Funding
- Fundacao de Amparo a Pesquisa do Estado de Sao Paulo [2013/12993-4]
- Conselho Nacional de Desenvolvimento Cientifico e Tecnologico
- Ministry of Education, Youth and Sports of the Czech Republic [CEITEC 2020 (LQ1601)]
- Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior
- CEITEC Nano Research Infrastructure [MEYS CR (LM2018110)]
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The development of stable and reproducible inorganic pigments is noteworthy for industrial applications mainly considering more intense shades and low toxicity. Among the various candidates to substitute non-hazardous red and yellow pigments, CeO(2)and CeO2:Pr have been attracting attention because of their opacity and high-temperature stability besides being environmental-friendly and health-friendly. In this study, nanostructured CeO(2)and CeO2:Pr samples were synthesized using the polymeric precursor method and structural and optical characterizations were performed. Scanning electron microscopy reveals the morphology of CeO(2)nanoparticles in which the particle size ranges from 22 to 28 nm as a function of the annealing temperature. Pr-doping does not show influence on the particle size. XRD results show that CeO(2)and CeO2:Pr samples crystallize in the cubic fluorite lattice withFm3mspace group. Raman spectra show the fluorite F(2g)mode, confirming the XRD results. With Pr-doping and the annealing of the samples, two bands are observed between 550 and 600 cm(-1), which are related to the defects in the fluorite structure associated with oxygen vacancies. XPS spectra reveal an increase in the ratio of Ce(3+)ions depending on the annealing temperature and Pr-doping. This increase is associated with the carbon removal from the lattice by annealing. This behavior causes a change in the hue of the powders as the annealing temperature increases. According to diffuse reflectance and colorimetric measurements, CeO(2)shows a light-yellow color due to the O 2p-Ce 4f transitions whose b* parameter mainly decreases with annealing, becoming almost white. The CeO2:Pr sample exhibits a red-orange color because of the electronic transitions between 4f(2) -> 5d(1)states of Pr3+. Upon annealing, L* and b* parameters decrease, resulting in a red-brown shade. The charge compensation or charge transfer is responsible for the modification of the hue of these pigments.
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