Reversible nano-structuring of SrCrO3-δ through oxidation and reduction at low temperature

Abstract

Oxygen vacancies are often present in complex oxides as point defects, and their effect on the electronic properties is typically uniform and isotropic. Exploiting oxygen deficiency in order to generate controllably novel structures and functional properties remains a challenging goal. Here we show that epitaxial strontium chromite films can be transformed, reversibly and at low temperature, from rhombohedral, semiconducting SrCrO 2.8 to cubic, metallic perovskite SrCrO 3-d . Oxygen vacancies in SrCrO 2.8 aggregate and give rise to ordered arrays of {111}-oriented SrO 2 planes interleaved between layers of tetrahedrally coordinated Cr 4 þ and separated by B1 nm. First-principle calculations provide insight into the origin of the stability of such nanostructures and, consistent with the experimental data, predict that the barrier for O 2 À diffusion along these quasi-two-dimensional nanostructures is significantly lower than that in cubic SrCrO 3-d . This property is of considerable relevance to solid oxide fuel cells in which fast O 2 À diffusion reduces the required operating temperature.

Hole-induced insulator-to-metal transition inLa1−xSrxCrO3

“…The pure SrCrO 3 films were subjected to an additional anneal in air at 250 o C for 3 hours to insure complete oxidation and formation of the perovskite phase. 22 This step was found to not be important for LSCO films grown on LaAlO 3 (001), because upon air annealing, the changes in resistivity were negligible (see Fig. S1).…”

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

“…Ionics has been traditionally used for long-standing energy applications, 1,2 i.e., ion batteries which rely on the ionic motion of either Li or Na; [3][4][5][6][7][8][9][10] solid oxide fuel cells based on the ionic motion of either oxygen or hydrogen; [11][12][13][14] and catalysts which use oxidation and reduction processes of O 2 or CO 2 , [15][16][17] and so on. In these applications, compared with electronic motion, ionic motion is essentially very slow, 18 resulting in many unsolved challenges.…”

Comparison of topotactic fluorination methods for complex oxide films

“…For example, post-growth anneals in oxygen, dilute O 3 /O 2 mixtures, vacuum, or forming gas mixtures have been used to oxidize or reduce, depending on the annealing environment, many ABO 3−δ perovskites to achieve a targeted anion stoichiometry, typically δ = 0 or 0.5. [2][3][4][5][6][7][8][9][10][11] The use of aggressive reducing agents, such as Ca 2 H, 12 has enabled the realization of ABO 2 compounds such as SrFeO 2 and LaNiO 2 via topotactic transformations from as-grown ABO 3 and ABO 2.5 films. 13,14 Given the sensitive coupling between δ and physical properties, [15][16][17] topotactic oxidation and reduction reactions have been used to induce large changes to the electronic, optical, and magnetic properties of epitaxial films [18][19][20] and may prove applicable in ionically controlled solid state devices.…”