Strain Tuning and Strong Enhancement of Ionic Conductivity in SrZrO₃–RE₂O₃ (RE = Sm, Eu, Gd, Dy, and Er) Nanocomposite Films

Abstract

wileyonlinelibrary.comThe tensile strain reduces the activation energy for oxygen vacancy migration because the spatial volume of the moving species increases. [ 12 ] In a lateral multilayer system composed of Y-stabilized ZrO 2 (YSZ) and RE 2 O 3 (RE = Y, Lu, and Sc), the ionic conductivity changed systematically depending on the strain state of the YSZ induced by the RE 2 O 3 layers. [ 9,11 ] Interestingly, ionic conductivity in YSZ/Y 2 O 3 multilayers increased by a few orders of magnitude, compared with bulk YSZ fi lm, due to very large tensile strain of 3% in YSZ layer induced by Y 2 O 3 layer.To date few systematic studies have been done to show how ionic conductivity scales with strain. [9][10][11] Owing to limitations on the availability of single crystal substrates and the diffi culty of probing buried planar interfaces, the infl uence of strain alone on the ionic conduction cannot be easily investigated in standard planar structures. Hence, controversy remains over the true origin of the enhanced ionic conduction at interfaces. Further complications in understanding arise because space charge effects and reconstruction (i.e., formation of interface defects such as dislocations and oxygen vacancies), can also contribute to the enhanced ionic conductivity. [ 3,4 ] In vertical nanoscaffold fi lms, the strain is controlled in the out-of-plane direction because vertical heteroepitaxial matching occurs between two epitaxial oxides within the fi lm, instead of between the fi lm and substrate in the standard planar fi lm case. [ 8,[13][14][15][16][17][18][19] Hence, nanoscaffold fi lms offer the following advantages over planar fi lms: a. By choosing the appropriate two phases in a nanoscaffold fi lm, one phase in the fi lm will act as a stiff, strain-controlling phase, while the other phase (which forms the matrix) will be strain-controlled. [ 8,[13][14][15][16][17][18][19] Hence, by using different second phase materials to systematically control the strain, there is the possibility to understand the role of strain independent of the infl uences of charge and surface reconstruction effects. b. Since the lateral dimensions of the two phases in the fi lm are only tens of nm, vertical strains of more than 2% can be induced, independent of fi lm thickness. [ 16,17 ] Also, the vertical strain remains in much thicker fi lms and is independent of the substrate (when the fi lm thickness is larger than a critical fi lm thickness), which is not the case of standard planar fi lms, Fast ion transport channels at interfaces in thin fi lms have attracted great attention due to a range of potential applications for energy materials and devices, for, solid oxide fuel cells, sensors, and memories. Here, it is shown that in vertical nanocomposite heteroepitaxial fi lms of SrZrO 3 -RE 2 O 3 (RE = Sm, Eu, Gd, Dy, and Er) the ionic conductivity of the composite can be tuned and strongly enhanced using embedded, stiff, and vertical nanopillars of RE 2 O 3 . With increasing lattice constant of RE 2 O 3 from Er 2 O 3 to Sm 2 O 3 , i...

Role of scaffold network in controlling strain and functionalities of nanocomposite films

“…The measured strain is consistently smaller than the calculated lattice mismatch in all reported systems. Table S2 summarizes the composite films with domain matching ( 12 , 17 , 24 , 27 , 29 , 38 , 39 ). The overall calculated misfit strain is small and less than 3.32%.…”

Interfacial lattice-strain effects on improving the overall performance of micro-solid oxide fuel cells

“…[31][32][33][34][35] For instance, porous electrode materials have been employed to improve the efficiency of gas transport in the SOFC technology, which decreases the concentration polarization of gas transport in electrodes. 50,51 Fig. [39][40][41][42][43][44][45][46] An insightful review has been provided by Yildiz recently, 47 which focuses strongly on computational aspects and some model experiments carried out on the strain-ionic transport interaction in oxide films.…”

Research Update: Fast and tunable nanoionics in vertically aligned nanostructured films

“…Very recently, as shown in Figure 1(d), new and novel device architectures, vertically aligned nanostructured (VAN) films, [43][44][45][46][47][48][49][50][51][52][53] were developed to overcome several issues in conventional ionic devices as mentioned above. Basically, the development of ionic devices by using VAN films started from a similar motivation of laterally aligned heteroepitaxy films.…”

“…In this section, we will introduce several interesting examples, such as memories using RS phenomena, 46 oxide fuel cells, 43,[47][48][49][50] and water splitting. 53 Further applications, as yet unexplored, would be entirely possible by tailoring the various properties of VAN films.…”