Tuning Color through Sulfur and Fluorine Substitutions in the Defect Tin(II, IV) Niobate Pyrochlores

Published

July 1, 2018

Author(s)

Gabriella Giampaoli, Jun Li, Raphael P. Hermann, Judith K. Stalick, M. A. Subramanian

Abstract

Sulfur and fluorine substituted Sn₂Nb₂O6d7^ pyrochlore compounds were synthesized to produce brilliant orange/red colors as an environmentally friendly alternative to other toxic inorganic pigments. Neutron structure refinements indicate that the studied compositions crystallize in the pryochlore structure with a large number of cation and/or anion vacancies and significant local structural disorder. The cubic unit cell decreases with increasing sulfur and fluorine content and ¹¹⁹Sn Mossbauer analysis quantified the presence of both Sn²⁺ and Sn⁴⁺ in all compositions. The static displacive disorder and unusual lattice evolution with sulfur substitution are presumably driven by the strong lone pair steroactivity associated with Sn²⁺. Chemical analysis confirmed the the existence of sulfur and fluorine in these compounds. The general formula representative of sulfur-containing pigments is nonstoichiometric Sn^{2+6_2-z(Nb_2-ySn}u4+^_y)O_7-zy/2-xS_x with the color varying according to x, y and z values. The fluorine compound is refined to be Sn^{2+6₂(Nb_0.958Ti_0.984Sn}u4+^_0.058)Od6.376^F_0.206 with anion vacancies only. Optical characterization was performed through diffuse reflectance and color meter measurements. The estimated band gap is determined to be in the range of 2.35 to 2.05 eV as sample color changes from yellow to orange/red. All powder samples were found to have 6095% reflectance in the near-infrared (NIF) region, adding new functionality to the application of these compounds as "cool" pigments.

Citation

Solid State Sciences

Volume

81

Pub Type

Journals

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Keywords

pyrochlores, cool pigments, neutron Rietveld refinement, lone pair stereoactivity, color tuning

Citation

Giampaoli, G. , Li, J. , Hermann, R. , Stalick, J. and Subramanian, M. (2018), Tuning Color through Sulfur and Fluorine Substitutions in the Defect Tin(II, IV) Niobate Pyrochlores, Solid State Sciences, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=925844 (Accessed December 8, 2024)