“Energy Selection Channels” for High-Performance Electrolyte: Anion-Frenkel Defect Pair as Dominant Source for O Ion Conductions in Pyrochlore-type Lanthanide Hafnium Oxides SOFC

Abstract

The excellent ion conductivities of pyrochlore-type materials are believed to be based on oxygen anion transportations caused by the intrinsic defects, in which the anion Frenkel (a-Fr) pair (V+I) defect is the most stable one that lacks detailed study. The partially disordered pyrochlore with formation of the a-Fr pair defect will result in more disorder in local pyrochlore structure and increase number of possible migration paths for oxygen anions, which could further improve the ion conductivities of materials. Hence, we studied the formation of a-Fr defect pairs in LaHfO as a representative pyrochlore structure by density functional theory (DFT) calculations. Three types of defect migration sites were discovered with the ability to incorporate interstitial oxygen atoms from 48f sites and form a-Fr defect pairs (I+V). Besides the most stable vacant 8a sites with lowest defect formation energy of 3.49 eV/pair, two other novel migration sites have been first reported with ability to form a-Fr pair defect with formation energies of 6.53 and 8.49 eV/pair, respectively. These two new types of migration path, as intermediate sites, could construct a diffuse channel with vacant 8a site for interstitial oxygen anions diffusion in the lattice and significantly decrease the distance and barrier of each jump for oxygen atoms. In contrast with the oxygen interstitial defects, the formation of a-Fr pair defect shows higher priority because of much lower formation energies. Since oxygen anions could be easier to generate and diffuse in the pyrochlore structure, the a-Fr pair defect can be explained as the origin of excellent ion conductivities of pyrochlore materials. This work provides a detailed understanding of relationship between intrinsic defects and electronic properties, which enable us to predict electronic properties of other pyrochlore-type materials in the future study.

Multicolor Tuning and Temperature-Triggered Anomalous Eu3+-Related Photoemission Enhancement via Interplay of Accelerated Energy Transfer and Release of Defect-Trapped Electrons in the Tb3+,Eu3+-Doped Strontium–Aluminum Chlorites

“…We further perform on the energetic behaviors of different substitution dopings in the host matrix. To illustrate the dependence of temperature on the free energy in the system, the thermodynamic principles are imported to discuss the stability. , The free energy as a function of temperature is based on the phonon calculation which is based on one of the inset functionals of our CASTEP packages. Thermodynamic calculations can be performed only if the system is in the ground state, that is, geometry optimization is fully converged.…”

All-inorganic perovskite nanocrystals: next-generation scintillation materials for high-resolution X-ray imaging

“…Having severe impacts on thermal conductivity and ionic conduction, [38][39][40] the anion Frenkel (a-Fr) defects serve as the dominant imperfection type in fluorides and oxides lattice, formed by an anion moving from its original site to a neighboring interstitial site, resulting in an uncharged vacancy-interstitial defect pair in the lattice. 38,39,41,42 The migrating charge carriers can be trapped and stored in these defect states, mainly in those of vacancies. The electrons/holes in traps will be released by ambient thermal disturbance, followed by phonon-assisted migration.…”

Synthesis and Thermodynamic Properties of the Ln2CrTaO7 (Ln = Sm, Gd, Y) Pyrochlores

“…Compounds with a pyrochlore structure are of great interest due to the possibility of their use for solving a number of significant problems, such as the creation of fuel cells [1][2][3][4], microwave technology materials [5], visible-light photocatalysts for water and organic dyes decomposition [6][7][8], CO oxidation catalysts [9], phosphors [10,11], ceramic pigments [12], and ceramics for nuclear waste disposal [13][14][15]. Also, the attention of researchers is focused on their magnetic [16,17] and electrical properties [3,18,19].…”