The ability to manipulate oxygen anion defects rather than metal cations in complex oxides can facilitate creating new functionalities critical for emerging energy and device technologies. However, the difficulty in activating oxygen at reduced temperatures hinders the deliberate control of important defects, oxygen vacancies. Here, strontium cobaltite (SrCoOx) is used to demonstrate that epitaxial strain is a powerful tool for manipulating the oxygen vacancy concentration even under highly oxidizing environments and at annealing temperatures as low as 300 C. By applying a small biaxial tensile strain (2%), the oxygen activation energy barrier decreases by ~30%, resulting in a tunable oxygen deficient steady-state under conditions that would normally fully oxidize unstrained cobaltite. These strain-induced changes in oxygen stoichiometry drive the cobaltite from a ferromagnetic metal towards an antiferromagnetic insulator. The ability to decouple the oxygen vacancy concentration from its typical dependence on the operational environment is useful for effectively designing oxides materials with a specific oxygen stoichiometry.
Simultaneous study of magnetic and electrocatalytic properties of cobaltites under extreme conditions expands understanding of physical and chemical processes proceeding in them with the possibility of their further practical application. Therefore, La0.6Sr0.4CoO3 (LSCO) nanopowders have been synthesized at different annealing temperatures tann = 850, 875, 900 C, and their multifunctional properties have been studied comprehensively. As tann increases, the rhombohedral perovskite structure of the LSCO becomes more single-phase, whereas average particle size and dispersion grow. Co ions are in …
Oxygen Vacancies at Dislocation Core Modulate Plasticity in Strontium Titanate
Ames National Laboratory（艾姆斯国家实验室）；North Carolina State University（北卡罗来纳州立大学）；Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院）；Iowa State University（爱荷华州立大学）；University of Virginia（弗吉尼亚大学）
Supercapacitors have recently gained popularity as possible energy storage systems due to their high cycling ability and increased power density. However, one of the major drawbacks of supercapacitors is that they have a low energy density, which makes them less effective than batteries. Herein, we explore different methods of increasing the supercapacitor performance of the perovskite SrCoO3. We carry out first-principles calculations to systematically study how SrCoO3/graphene interface, oxygen vacancies, and doping improve the performance of strontium cobaltite as an anion-intercalation-typ…
Strontium doped lanthanum manganite thin films were deposited by pulsed laser deposition on yttria stabilized zirconia single crystals for a comprehensive electrochemical characterization of the material acting as a cathode. A physically meaningful electrical model was employed to fit the electrochemical impedance spectroscopy results in order to extract the main oxygen mass transport parameters as a function of the temperature and oxygen partial pressure. The oxygen diffusion and surface exchange coefficients extracted from the analysis showed several orders of magnitude of enhancement with r…
Strontium cobaltite (SrCoOx) is known as a material showing fast topotactic electrochemical Redox reaction so-called oxygen sponge. Although atomic scale phenomenon of the oxidation of SrCoO2.5 into SrCoO3 is known, the macroscopic phenomenon has not been clarified yet thus far. Here, we visualize the electrochemical oxidation of SrCoOx macroscopically. SrCoOx epitaxial films with various oxidation states were prepared by the electrochemical oxidation of SrCoO2.5 film into SrCoO3-d film. Steep decrease of both resistivity and the absolute value of thermopower of electrochemically oxidized SrCo…
Since oxide materials like Sr$_2$FeMoO$_6$ are usually applied as thin films, we studied the effect of biaxial strain, resulting from the substrate, on the electronic and magnetic properties and, in particular, on the formation energy of point defects. From our first-principles calculations, we determined that the probability of forming point defects - like vacancies or substitutions - in Sr$_2$FeMoO$_6$ could be adjusted by choosing a proper substrate. For example, the amount of anti-site disorder can be reduced with compressive strain in order to obtain purer Sr$_2$FeMoO$_6$ as needed for sp…
Magnetic properties of bilayer Sr$_3$Ir$_2$O$_7$: role of epitaxial strain and oxygen vacancies
用{ \it ab initio}方法研究了SrIridates Ruddlesden-Popper系列SrPDMATHABMO Ir $_{m}$ O $_{3m+1}$，双层结构SrPDMATHABMR Ir $_2$ O $_7$的磁性随外延应变和氧空位的变化.与单层化合物Sr $_2$ IrO $_4$不同，其表现出稳健的面内磁序，Sr $_3$ Ir $_2$ O $_7$中的面内和面外磁序之间的能量差小得多，并且预计小的外部扰动可以诱导磁跃迁。我们的研究结果表明，外延应变产生的自旋翻转转变，这是由之间的交叉层$J_1$和层间$J_2$磁交换相互作用压缩应变。$J_1$对应变效应基本上不敏感，而$J_2$的强度在拉伸应变$\geq$ 3~ 1%时变化一个数量级。此外，我们的研究澄清了不寻常的平面内观察到的磁响应在Sr $_3$ Ir $_2$ O $_7$的应用程序时的外部磁场源于由于氧空位，倾斜的八面体网络的局部磁矩的倾斜-从而允许非共线的自旋配置。
Magnetism in lanthanum cobaltite (LCO, LaCoO$_3$) appears to be strongly dependent on strain, defects, and nanostructuring. LCO on strontium titanate (STO, SrTiO$_3$) is a ferromagnet with an interesting strain relaxation mechanism that yields a lattice modulation. However, the driving force of the ferromagnetism is still controversial. Experiments debate between a vacancy-driven or strain-driven mechanism for the ferromagnetism of epitaxial LCO. We found that a weak lateral modulation of the superstructure is sufficient to promote ferromagnetism. We find that ferromagnetism appears under unia…
SrTiO$_3$, a quantum paralectric, displays a detectable phonon thermal Hall effect (THE). Here we show that the amplitude of THE is extremely sensitive to stoichiometry. It drastically decreases upon substitution of a tiny fraction of Sr atoms with Ca, which stabilizes the ferroelectric order. It drastically increases by an even lower density of oxygen vacancies, which turn the system to a dilute metal. The enhancement in the metallic state exceeds by far the sum of the electronic and the phononic contributions. We explain this observation as an outcome of three features: i) heat is mostly tra…
Room temperature ferromagnetism was characterized for thin films of SrTi$_{0.6}$Fe$_{0.4}$O$_{3-δ}$ grown by pulsed laser deposition on SrTiO$_{3}$ and Si substrates under different oxygen pressures and after annealing under oxygen and vacuum conditions. X-ray magnetic circular dichroism demonstrated that the magnetization originated from Fe$^{2+}$ cations, whereas Fe$^{3+}$ and Ti$^{4+}$ did not contribute. Films with the highest magnetic moment (0.8 μB per Fe) had the highest measured Fe$^{2+}$:Fe${^3+}$ ratio of 0.1 corresponding to the largest concentration of oxygen vacancies (δ = 0.19). …
Strontium titanate (SrTiO3) is widely used as a promising photocatalyst due to its unique band edge alignment with respect to the oxidation and reduction potential corresponding to oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). However, further enhancement of the photocatalytic activity in this material could be envisaged through the effective control of oxygen vacancy states. This could substantially tune the photoexcited charge carrier trapping under the influence of elemental functionalization in SrTiO3, corresponding to the defect formation energy. The charge trappi…
