| Abstrakt: |
Phase equilibria and structural transformations in the ternary ZrO2–La2O3–Gd2O3 system at 1600°C were studied by X-ray diffraction, microstructural, and electron microprobe analyses over the entire composition range. Fields of solid solutions based on the cubic fluorite-type (F) and tetragonal (T) modifications of ZrO2, monoclinic (M) and cubic (C) modifications of Gd2O3, hexagonal (A) modification of La2O3, and an ordered intermediate phase with La2Zr2O7 pyrochloretype structure (Py) exist in the system. The boundaries of phase fields and lattice parameters of the phases were determined. In the ZrO2-rich corner, solid solutions based on the ZrO2 tetragonal modification are formed. The solubility of La2O3 in the T-ZrO2 lattice is low and reaches ~0.5 mol.%, which is evidenced by X-ray diffraction and microstructural analyses. The solid solutions based on the tetragonal modification of zirconia cannot be quenched when cooled with the furnace. The diffraction patterns recorded at room temperature include peaks of the M-ZrO2 monoclinic phase. The ordered Ln2Zr2O7 pyrochlore-type (Py) phase is in equilibrium with all phases (except for C-Gd2O3) existing in the ternary ZrO2–La2O3–Gd2O3 system at 1600°C and forms substitutional solid solutions with phases of the binary systems. The greatest solubility in the Ln2Zr2O7 (Py) lattice is shown by Gd2O3 along the Gd2O3–(67 mol.% ZrO2–33 mol.% La2O3) section. The La2Zr2O7 (Py) lattice parameters change from a = 1.0781 nm for the single-phase (Py) sample containing 67 mol.% ZrO2–33 mol.% La2O3–0 mol.% Gd2O3 to a = 1.0741 nm for the threephase (F + Py + B) sample containing 43.55 mol.% ZrO2–21.45 mol.% La2O3–35 mol.% Gd2O3 along the Gd2O3–(67 mol.% ZrO2–33 mol.% La2O3) section. The cubic phases are primarily in equilibrium in the ZrO2–La2O3–Gd2O3 system: F-Fm3m, Py-Fd3m, and C-Ia3. The isothermal section of the ZrO2–La2O3–Gd2O3 phase diagram at 1600°C contains four three-phase regions (T + F + Py, A + Py + B, Py + F + B, and F + C + B) and nine two-phase regions (T + Py, F + Py, F + T, F + C, F + B, B + Py, A + Py, B + A, and B + C). [ABSTRACT FROM AUTHOR] |
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