Low‐Temperature Phase Equilibria by the Flux Method and the Metastable–Stable Phase Diagram in the ZrO₂–CeO₂ System

Abstract

Low-temperature phase equilibria ranging from 1000" to 1200°C in the Zr0,-CeO, system were investigated by annealing compositionally homogeneous Zr0,-CeO, solid solutions in a Na,B,O,.NaF flux. The 5 mol% CeO, samples decomposed into monoclinic ( m ) and tetragonal ( t ) phases during annealing at 1100" and 1120"C, and the t-phase transformed diffusionlessly into monoclinic (m') symmetry during quenching. A eutectoid reaction, t +-( m + c), was confirmed to occur at 1055" +. 1O"C, where the equilibrium compositions of the t-, m-, and c-phases were 11.2 +: 2.8, 0.9 f 0.9, and 84 ? 1 mol% CeO,, respectively. The equilibrium phase boundaries were almost independent of the annealing time and/or the flux:sample ratio, which indicates that the flux accelerates the reaction rate without affecting the equilibration. The previous data are discussed using metastable-stable phase diagrams. The discrepancies of the low-temperature phase diagram in the literature are attributable to either regarding the metastable phase boundaries as stable ones or ignoring the sluggish kinetics.

Humidity Related Low Temperature Conductivity Hysteresis of Ce1–xZrxO2 (0 ≤ x ≤ 1) Ceramics. Structural Disorder Relationship

“…In agreement with reported phase diagrams [5][6][7]9], monoclinic, tetragonal and cubic phases are detected when the amount of Ce increases. As a consequence of the low miscibility of Zr and Ce cations, the simultaneous presence of tetragonal Zr rich and cubic Ce rich phases should be produced at intermediate 0.4 < x < 0.8 compositions.…”

“…According to the widely accepted phase-diagram established by Yashima et al, [6] the segregation of Ce-poor tetragonal (x > 70%), and Ce-rich cubic phases (x < 40%) should be produced at intermediate compositions. However, some complexity arises from the existence of metastable t′ and t″ tetragonal phases that improves cation mixing at intermediate compositions [7].…”

Sol–Gel Synthesis of Tunable Cerium Titanate Materials

“…Yashima et al [16] have reviewed the phase diagram and phase transition in the CeO 2 -ZrO 2 system. In the Ce-rich area a cubic phase is detected, meanwhile in the Zr-rich area the monoclinic phase is stabilized.…”

Electrical conductivity of metastable κ-CeZrO4 phase possessing ordered arrangement of Ce and Zr ions

“…The electrical conductivity of xCeO 2 ±(1 2 x)ZrO 2 oxides has been investigated at intermediate temperatures as 1273 K over the wide composition range [3]. In the intermediate composition range of the CeO 2 ±ZrO 2 system, no compound exists in the equilibrium phase diagram, except for the CaF 2 -type cubic phase over 1823 K [4,5]. When it is cooled in the furnace, in spite of its low cooling rate, a tetragonal t 0 or t 00 phase possessing random distribution of Ce and Zr ions could appear without the phase separation [6,7].…”