Heterophase synthesis of rare-earth zirconates

Abstract

This study focuses on developing a heterophase process for synthesizing rare-earth zirconates, specifically R2Zr2O7 /R2O3·2ZrO2 (R = La, Sm, Gd, Dy). We investigated the sorption properties of low-hydrated zirconium hydroxide, a precursor for complex-oxide phases, towards rare-earth elements' ions (La, Sm, Gd, Dy). The results indicate that sorption by low-hydrated zirconium hydroxide is a multifaceted process, involving the incorporation of rare-earth cations into the pores of low-hydrated hydroxide and ion exchange. The paper details the synthesis of R2Zr2O7 /R2O3·2ZrO2 (R = La, Sm, Gd, Dy), considering both «light» and «heavy» elements. The process process involves the interaction between Zr(OH)3÷1O0.5÷1.5·(1.6÷2.6)H2O, low-hydrated zirconium hydroxide, and an aqueous solution of rare-earth acetate (С(La3+) = 0.155 mol/l, С(Sm3+) = 0.136 mol/l, С(Gd3+) = 0.141 mol/l, С(Dy3+) = 0.120 mol/l) followed by heat treatment. The resulting phases and their thermolysis products were analyzed using differential thermal analysis and X-ray phase analysis. Single-phase rare-earth zirconates R2Zr2O7 (R = La, Sm, Gd) and the Dy2O3·2ZrO2 solid solution were only obtained at 800 °С. The lattice parameters are calculated for each phase. Lanthanum, samarium, and gadolinium zirconates exibited a cubic pyrochlore structure (Fd3–m), while dysprosium displayed a fluorite structure (Fm3–m). The average particle size of all zirconates was 1.14 ± 0.02 μm.