Abstract
This study combines bulk structural and spectroscopic investigations of Eu3+- or Y3+/Eu3+ co-doped tetragonal and cubic zirconia polymorphs to gain an in-depth understanding of the solid solution formation process. Our bulk structural characterizations show that the dopant is homogenously distributed in the ZrO2 host structure resulting in an increase of the bulk symmetry with increasing dopant substitution (from 8 to 26 mol%). The local site symmetry around the Eu3+ dopant, however, determined with luminescence spectroscopy (TRLFS), remains low in all samples. Results obtained with X-ray pair distribution function and X-ray absorption spectroscopy show that the average coordination environment in the stabilized zirconia structures remains practically unchanged. Despite this very constant average dopant environment, site-selective TRLFS data show the presence of three nonequivalent Eu3+ environments in the ZrO2 solid structures. These Eu3+ environments are assumed to arise from Eu3+ incorporation at superficial sites, which increase in abundance as the size of the crystallites decrease, and incorporation on two bulk sites differing in the location of the oxygen vacancies with respect to the dopant cation.
Highlights
Zirconia (ZrO2) is a material with exceptional properties such as a very high melting point of 2715 °C and the capability of forming solid solutions with various isovalent and aliovalent cations [1]
Our bulk structural characterizations show that the dopant is homogenously distributed in the ZrO2 host structure resulting in an increase of the bulk symmetry with increasing dopant substitution
Results obtained with X-ray pair distribution function and X-ray absorption spectroscopy show that the average coordination environment in the stabilized zirconia structures remains practically unchanged
Summary
Zirconia (ZrO2) is a material with exceptional properties such as a very high melting point of 2715 °C and the capability of forming solid solutions with various isovalent and aliovalent cations [1]. The fracture toughness rests upon the martensitic transformation of metastable t-ZrO2 to mZrO2, which is accompanied by a volumetric expansion This expansion resulting from the diffusionless transformation, induced by the stress field around a crack in a ZrO2 ceramic material, leads to local compressive stress which counterweighs the driving force of the crack propagation [1, 14,15,16]. For applications as nuclear materials, the crystalline host structure must be flexible enough to accommodate the rather large actinide cations Structural properties such as a large overall grain size and low porosity, which reduce the reactive surface area and subsequently increase their corrosion resistance in contact with water, are important
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