Beneficial Lattice Strain in Heterogeneously Doped Ceria

Abstract

Oxygen ion conduction in heterogeneously doped films composed of alternating layers of pure Y2O3 and pure CeO2 was reported recently, with conduction coming predominantly from vacancies trapped in interfacial space charge regions in CeO2. Here, we expand this concept to films composed of CeO2 heterogeneously doped with Y2O3, Gd2O3, or La2O3 in order to study the effects of heterodopant identity on the oxygen ion conductivity. For all samples, the thickness of the entire structure and that of the individual dopant layers were kept constant. The dopant oxides used in this work adopt the cubic bixbyite crystal structure with pseudo-fluorite lattice parameters that are, relative to CeO2, smaller (Y2O3), larger (La2O3), and nearly equal (Gd2O3). The total conductivity of the films increased with increasing lattice parameter of the dopant oxides. An electrostatic Gouy–Chapman model is not sufficient to explain this behavior because all of the dopants theoretically contribute identical interfacial oxygen vacancy concentrations. Therefore, extensions beyond a Gouy–Chapman model are suggested, with consideration for the effects of interfacial strain on the concentration and mobility of vacancies from dopant oxides in the space charge region.

Colossal oxygen vacancy formation at a fluorite-bixbyite interface

“…13). Therefore, the (111) fluorite-bixbyite interface could induce a larger number of oxygen vacancies without the creation of an SCR, which differs from the mechanism proposed for (001) interfaces of fluorite-bixbyite systems in previous studies 15,16 . As was confirmed by STEM imaging, classical force field (FF) simulation also confirmed that the CeO 2 side of the interfaces always remained as the fluorite structure, even though the interface had a high concentration of oxygen vacancies ( Supplementary Fig.…”

“…It was proposed that a space charge region (SCR) [12][13][14] could be formed by interfacing the fluorite CeO 2 (space group Fm 3m, a = 5.412 Å) with a bixbyite oxide, such as Y 2 O 3 (space group Ia 3, a = 10.607 Å), along the [100] direction 15,16 . The bixbyite structure has a "pseudofluorite" structure with an ordered array of vacant oxygen sites occurring on every fourth site (Supplementary Fig.…”

Controlling Oxygen Mobility in Ruddlesden–Popper Oxides

“…The use of epitaxial strain induced in a thin film by lattice mismatch with a substrate has been intensively studied for control of oxygen migration and the formation of oxygen defects in binary oxides [ 80 , 81 , 82 , 83 , 110 , 111 , 112 , 113 , 114 ] and ABO 3 perovskite oxides [ 7 , 85 , 86 , 115 , 116 , 117 , 118 , 119 ]. Theoretical studies [ 110 , 112 ] have shown that tensile (compressive) strain can decrease (increase) the formation energy of oxygen vacancies in CeO 2 .…”

Equilibrium oxygen storage capacity of ultrathin CeO2-δ depends non-monotonically on large biaxial strain

“…Numerous studies have investigated the effect of strain on the surface reactivity using substrate-supported films 12 13 14 15 and on ionic transport using multilayered heterostructures 16 17 18 19 20 21 22 23 . In the latter, a wide variation in the results is often observed depending on the volume fraction of the strained phases and the geometry of electrical contacts, among other parameters 20 21 22 23 24 . It is generally recognized that compressive strain increases the migration barrier for oxygen ion transport and surface exchange, while tensile strain has the opposite effect.…”