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Effect of Rare-Earth (RE) Cation Size on Phase Stability and Grain Growth of RE2Zr2O7 (RE = La, Gd, Yb, and Y) at 1100, 1200, and 1300 °C.

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Title: Effect of Rare-Earth (RE) Cation Size on Phase Stability and Grain Growth of RE2Zr2O7 (RE = La, Gd, Yb, and Y) at 1100, 1200, and 1300 °C.
Authors: Hedayati, Omid1 (AUTHOR), Farvizi, Mohammad2 (AUTHOR) mmfarvizi@yahoo.com, Rahimipour, Mohammad Reza1 (AUTHOR), Bahamirian, Milad3 (AUTHOR)
Source: Journal of Materials Engineering & Performance. May2026, Vol. 35 Issue 17, p16520-16536. 17p.
Subjects: Rare earth ions, Pyrochlore, Zirconium compounds, Crystal growth, Heat treatment, Thermal barrier coatings, Phase equilibrium
Abstract: This study investigates the effect of rare-earth (RE) cation size on phase stability and grain growth behavior in RE2Zr2O7 zirconates (RE = La3+, Gd3+, Yb3+, and Y3+) synthesized via coprecipitation and subjected to thermal treatments at 1100, 1200, and 1300 °C for up to 50 h. High-temperature x-ray diffraction (HT-XRD) and Raman spectroscopy reveal that the crystallization onset temperature increases with the size of the RE cation, occurring at 700 °C for YbZO and YZO, 800 °C for GdZO, and 900 °C for LaZO. Larger RE cations favor formation and stability of the ordered pyrochlore structure, while smaller cations promote the defect fluorite structure at lower temperatures. Heat treatment induces a gradual phase transition from defect fluorite to pyrochlore, with the cation order parameter remaining consistently high in LaZO (ΦC = 1), while increasing significantly in the other compositions after 50 h at 1300 °C—from 0.41 to 0.97 in GdZO, 0 to 0.73 in YbZO, and 0 to 0.33 in YZO. FESEM analysis shows grain growth from 72 to 134 nm in LaZO, 47 to 116 nm in GdZO, 33 to 112 nm in YbZO, and 26 to 123 nm in YZO after 50 h at 1300 °C, with smaller cation samples exhibiting faster growth due to lower activation energies. These findings demonstrate that RE cation size critically controls phase stability and microstructural evolution, providing a basis for optimizing thermal barrier coatings with enhanced sintering resistance and thermal performance. [ABSTRACT FROM AUTHOR]
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Abstract:This study investigates the effect of rare-earth (RE) cation size on phase stability and grain growth behavior in RE2Zr2O7 zirconates (RE = La3+, Gd3+, Yb3+, and Y3+) synthesized via coprecipitation and subjected to thermal treatments at 1100, 1200, and 1300 °C for up to 50 h. High-temperature x-ray diffraction (HT-XRD) and Raman spectroscopy reveal that the crystallization onset temperature increases with the size of the RE cation, occurring at 700 °C for YbZO and YZO, 800 °C for GdZO, and 900 °C for LaZO. Larger RE cations favor formation and stability of the ordered pyrochlore structure, while smaller cations promote the defect fluorite structure at lower temperatures. Heat treatment induces a gradual phase transition from defect fluorite to pyrochlore, with the cation order parameter remaining consistently high in LaZO (ΦC = 1), while increasing significantly in the other compositions after 50 h at 1300 °C—from 0.41 to 0.97 in GdZO, 0 to 0.73 in YbZO, and 0 to 0.33 in YZO. FESEM analysis shows grain growth from 72 to 134 nm in LaZO, 47 to 116 nm in GdZO, 33 to 112 nm in YbZO, and 26 to 123 nm in YZO after 50 h at 1300 °C, with smaller cation samples exhibiting faster growth due to lower activation energies. These findings demonstrate that RE cation size critically controls phase stability and microstructural evolution, providing a basis for optimizing thermal barrier coatings with enhanced sintering resistance and thermal performance. [ABSTRACT FROM AUTHOR]
ISSN:10599495
DOI:10.1007/s11665-025-12819-6