PAC Characterization of Nontransformable Tetragonal t′ Phase in Arc‐Melted Zirconia–2.8 mol% Yttria Ceramics

Abstract

Tetragonal compact bodies obtained by quenching from the melt a ZrO 2 -2.8 mol% Y 2 O 3 commercial powder have been investigated between room temperature and 1150°C, using mainly perturbed angular correlations spectroscopy. The resulting nontransformable t phase observed by optical micrography is characterized at nanoscopic level by a hyperfine interaction describing defective and disordered Zr 4؉ neighborhoods very different from those of the regular tetragonal phase. A small amount of remaining Zr 4؉ sites corresponds to a scarcely distorted tetragonal structure. As the compacts are heated, two processes activate: the movement of vacancies and the gradual and irreversible conversion of t defective sites into less defective ones, probably resulting from oxygen absorption.

Room‐Temperature Degradation of t‐Zr(Pr)O2 in an Aqueous Suspension Revealed by Perturbed Angular Correlations

“…1(a)) reveal that the hyperfine interaction is made up of a unique and static EFG (•) characterized by ω Q =164 Mrad/s, η=0.51, and δ=22%, already reported for the same powder system 3 . This corresponds to the well‐known oxygen defective t ′‐form of metastable tetragonal zirconia 15 . The results obtained for the aqueous suspension (Fig.…”

Local Structures in the ZrO2–15 mol% Fe2O3 System Obtained by Ball Milling

“…As an example of the power of the technique, it must be mentioned that it has allowed the distinction of a variety of Zr surroundings within the metastable tetragonal structure. In fact, the existence of the regular t ‐form with eight oxygen‐coordinated Zr 4+ cations, it has been reported the ubiquitous and highly defective t ′‐form involving nearest oxygen vacancies, 12 the t ″‐form of null tetragonality 13 and the tetragonal form named X ‐configuration, 10 described by a very intense (ω≈180 Mrad/s), asymmetric, and ordered EFG.…”

Hyperfine Characterization of the Metastable t″‐Form of the Tetragonal Phase in ZrO2–10 mol% Y2O3 Powders Synthesized by Gel Combustion

“…The Perturbed Angular Correlations (PAC) method 10,11 has proved to be an efficient tool in the investigation of zirconia‐based ceramics at a nanoscopic level 12–14 . It allows the determination of different nanoconfigurations around zirconium sites, hardly resolvable by other techniques, as well as their thermal evolution without temperature limitations.…”

“…A goal of the PAC method has been the neat characterization of the two metastable tetragonal forms, t and t ′, that allowed separating them unambiguously in systems where both forms coexisted 11,13 . In fact, the corresponding spin rotation curves have been resolved in two quite distinct interactions (ω Q =165 Mrad/s, η≅0.55, and δ≥25% for metastable t ′‐form and ω Q =188 Mrad/s, η≅0.2, and δ≤4% for metastable t ‐form), also different from that of the equilibrium tetragonal phase 14 …”