Structural and Spectroscopic Study of a New Pink Chromium-Free Er2(Ti,Zr)2O7 Ceramic Pigment

Abstract

Transition metal ions are usually incorporated as chromophores into pyrochlore structures in order to develop colored compounds. However, due to the high toxicity of some of them (Cr, Ni, Co, Cd …), other nontoxic species such as lanthanide ions have been studied in order to produce environment-friendly pigments. This paper describes the structural and spectroscopic study of a pink pigment based on the Er2Ti2−xZrxO7 system synthesized by a sol–gel route. A previous research on the Er2Ti2O7 system revealed that this compound exhibits a pink coloration only in its defect fluorite-type structure. At high temperature (800°C), an atomic rearrangement into a pyrochlore network significantly reduces its coloration. The stabilization of the fluorite phase in Er2Ti2O7 through substitution of Ti(IV) with larger Zr(IV) ions is studied in this work. The analysis by differential thermal analysis and thermogravimetric analysis, X-ray powder diffraction, and Raman techniques indicates that the introduction of Zr(IV) species successfully avoids the undesired fluorite-to-pyrochlore transition. The colorimetric study concludes that the optimal composition corresponds to the Er2Ti0.6Zr1.4O7 stoichiometry, which gives an intense pink coloration independently of the thermal treatment. This study introduces a novel nontoxic pigment suitable for industrial applications at both low- and high-temperature ceramic technologies.