Diffusionless Tetragonal–Cubic Transformation Temperature in Zirconia–Ceria Solid Solutions

Abstract

Diffusionless tetragonal (t') u cubic (c') phase transformation in 65-mol%-Ce0,-ZrO2 was investigated around the c'-t' equilibrium temperature Ti'" using powder X-ray diffraction, where c' was defined as a tetragonal or cubic phase with an axial ratio of unity. The (400) peak profile of t'-ZrO, broadened at 860" and 900°C. This indicated that the t'-ZrO, transformed partially into c'-ZrO,. The (400) peak profile of c'-ZrO, also broadened at 860" and 9OO0C, which indicated that the c'-ZrO, partially transformed to t'-ZrO,. The finish point of t ' -d transformation T:' " was investigated by annealing the t'-ZrO, containing 30-65 mol% CeO, at various temperatures. The T:'"' line existed in the vicinity of the cubic solubility limit within the t + c two-phase region. This Tf-" location, which should have been located in the vicinity of Ti"", could not be explained by a simple regular solution model. However, it was described successfully by a thermodynamic model based on Landau's phenomenologic theory.

Synergy between gold and oxygen vacancies in gold supported on Zr-doped ceria catalysts for the CO oxidation

“…A classification of the crystallographic phase and the space group of Ce-Zr mixed oxides as a function of the Ce At.%, previously proposed by Yashima et al [34,35] is presented in Table 2. has been previously evidenced [8,36,37].…”

Supported Catalysts for CO2 Methanation: A Review

“…The t phase is a stable one and is formed through a diffusional phase decomposition; t' is obtained through a diffusionless transition and is metastable. The t" form is intermediate between t' and cubic [176][177][178][179]. The H2-TPR profiles reported in [180] show peaks in the temperature range from 400 °C to 600 °C for CZ, attributed to a reduction of surface oxygen and bulk oxygen in Ce0.5Zr0.5O2, respectively [42, 181,182], while the peaks around 360 °C are assigned to the reduction of surface oxygen in CZ and of the bulk NiO, having weak interaction with the support.…”

“…The t phase is a stable one and is formed through a diffusional phase decomposition; t' is obtained through a diffusionless transition and is metastable. The t" form is intermediate between t' and cubic [176][177][178][179].…”

Caracterización estructural y espectroscópica de fibras cristalinas de Ce_0.4Zr_0.6O₂ crecidas mediante el método de fusión zonal asistida por láser

“…In these conditions and under fast cooling rates, a cubic-like phase is quenched, with composition close to the starting one (x = 0.4). We attribute this phase to the defective phase named c' by Yashima et al (8), (16) However, reoxidation occurs at the surface of the rod during cooling, due to contact with air, up to a depth of several microns. That small region suffers the defective c' to non-defective t' phase transition also described by Yashima.…”

“…However, metastable phases of intermediate compositions (between ≈16 and 80 % Ce content) can be obtained by quenching from temperatures above 1600 ºC and applying a subsequent reoxidizing treatment. (8), (9) For compositions below 65 % the metastable t'-phase is formed, with the same P4 2 /nmc space group as tetragonal zirconia (t-ZrO 2 ), and c>a. On the other hand, the pseudocubic t''-phase found for Ce content between 65 and 80 % is also tetragonal, with the same space group as t' phase, but has c=a.…”