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Interface-engineered superlattices composed of perovskite PrCoO3 and brownmillerite CaCoO2.5 ([(PCO)n/(CCO)n]m) were designed and fabricated on (001) SrTiO3 substrates with integrated antiphase domain boundaries (APBs) for investigating ferromagnetic insulating phenomenon. The APBs were formed at the surface-step-terrace edges, and the densities of APBs can be regulated by the periods of the superlattices. In these superlattices, ferromagnetic insulating properties were found to be significantly modulated by the APBs. The room-temperature resistivity of the n = 1 superlattice increases by more than three orders of magnitude than that of the n = 5 superlattice and more than five orders of magnitude than that of the Pr0.5Ca0.5CoO3-δ alloy films. The insulation behavior is primarily derived from the charge carriers scattering at the APBs, which block the charge carriers transferring along the in-plane direction. These results could propel the advancement of multifunctional material genetics and provide a strategic approach for the development of artificial materials with tunable properties. [ABSTRACT FROM AUTHOR]

Interface-engineered double-perovskite structural LaBaCo2O5.5+δ thin films were highly epitaxially fabricated on (001) (La,Sr)(Al,Ta)O3 substrates with various miscut angles of 0°, 1°, 3° and 5° using a pulsed laser deposition system. All the LaBaCo2O5.5+δ thin films have a c-axis orientation with a highly epitaxial crystalline quality. Moreover, the effect of the interface tuning mechanism on the magnetic properties has been systematically investigated using physical properties measurement systems. Larger strain can be obtained by increasing the substrates’ surface miscut angles and can further enhance the magnetic properties of the LaBaCo2O5.5+δ thin films. All these results reveal that interface engineering using surface-step-terraces is an effective way of tuning/controlling the magnetic properties of LaBaCo2O5.5+δ films. [ABSTRACT FROM AUTHOR]

Surface exchange and oxygen vacancy diffusion dynamics were studied in double-perovskites LnBaCo2O5.5+δ (LnBCO) single-crystalline thin films (Ln=Er, Pr;20.5<δ<0.5) by carefully monitoring the resistance changes under a switching flow of oxidizing gas (O2) and reducing gas (H2) in the temperature range of 250 ∼8006C. A giant resistance change DR by three to four orders of magnitude in less than 0.1 s was found with a fast oscillation behavior in the resistance change rates in the DR vs. t plots, suggesting that the oxygen vacancy exchange diffusion with oxygen/hydrogen atoms in the LnBCO thin films is taking the layer by layer oxygen-vacancy-exchange mechanism. The first principles density functional theory calculations indicate that hydrogen atoms are present in LnBCO as bound to oxygen forming O-H bonds. This unprecedented oscillation phenomenon provides the first direct experimental evidence of the layer by layer oxygen vacancy exchange diffusion mechanism. [ABSTRACT FROM AUTHOR]

The role of temperature and the oxygen content in the structural transformation and electrical conductivity of epitaxial double perovskite LaBaCo2O5+δ (0≤ δ ≤ 1) thin films was systematically investigated. Reciprocal space mapping and ω-2θ x-ray diffraction performed at different temperatures in vacuum indicate that oxygen vacancies in the films become ordered at high temperature in a reducing environment. The changes of the oxygen content and the degree of oxygen vacancy ordering in the films result in a strong in-plane anisotropic lattice deformation and a large thermal expansion coefficient along the c-axis direction. The electrical conductivity measurements reveal that these behaviors are related to the degree of oxygen vacancy formation and lattice deformation in the films. [ABSTRACT FROM AUTHOR]

[Display omitted] • Quenching is utilized to produce advanced ceramic oxygen catalysts. • Quenching retains the high-temperature structure of oxygen catalysts. • Quenching improves catalytic activity and durability of ceramic catalysts for ORR. • Quenching determines the microstructural evolution of perovskite oxides. Rapid degradation of catalytic activity for oxygen reduction reaction has become key factor in restricting practical applications of perovskite oxide in solid oxide fuel cells. Herein, quenching is disclosed to be an effective method to bring rapid and durable oxygen catalysis of perovskite-structured Pr 0.5 Ba 0.25 Ca 0.25 CoO 3-δ. The quenching processing, cooling rate is around 8000 times higher than that of traditional annealing process, could turn the output power density of single cells from the decay process with a rate of 17.1% into an upsurge process with a rate of 18.4%, resulting in a stable power density of 0.72 W cm−2. This relates to a large number of point defects, dislocations, disorder and nanocrystalline domains are formed in perovskite oxides by quenching. These chemical defects can drive cationic diffusion to the surface indiscriminately, forming electroactive perovskite-structured nanoparticles. This work provides a new technology and concept to optimize the performance of perovskite-structured oxygen catalysts. [ABSTRACT FROM AUTHOR]

Distorted oxygen octahedral structures in complex oxides induced by deformations, tilts or rotations have emerged as a well-established approach to control the physical properties of functional oxide materials. In this work, the lateral magnetic anisotropy is modulated in highly epitaxial PrBaCo 2 O 5+δ (PBCO) thin films. Under the same growth conditions, a high density of anti-phase domain boundary (APB) defects is present in the PBCO films grown on (001)-oriented MgO substrate while less on (001)-oriented SrTiO 3 substrate. The APBs break the co-corner connection between oxygen octahedra, thereby changing the lattice symmetry and leading to different lateral magnetic anisotropy, i.e., the fourfold symmetric lateral magnetic anisotropy in PBCO/MgO while twofold symmetry in PBCO/SrTiO 3. Our results demonstrate that the magnetic anisotropy can be modulated through defect engineering, which can be further extended to a broader class of perovskite transition-metal oxides and pave the way for the development of correlated oxide-based magnetic spintronic devices. [Display omitted] [ABSTRACT FROM AUTHOR]

• Magic role of A-site cation size mismatch in the double perovskites is disclosed. • Lower M A relieves lattice distortion and expands PrO δ layer of double perovskites. • Lower M A stabilizes the surface chemistry of double perovskites. • Lower M A boosts the catalytic activity and durability of double perovskites in ORR. The double perovskite oxides are intriguing catalysts for energy conversion/storage and chemical sensor systems. The cation surface segregation is a stubborn issue that restricts their application. Herein, A-site cation size mismatch (M A) was proposed for the first time as a critical intrinsic parameter for controlling the surface chemistry and electrochemical performance of the double perovskite catalyst. The studies in PrBa 1-x Ca x CoCuO 5+δ revealed that lowering M A can relieve lattice distortion, enlarge PrO δ layer space, maintain surface chemistry, and significantly improve catalytic activity and durability of the double perovskite. Specifically, as M A decrease from 26.1–18.1 %, the output peak power density of PrBa 1-x Ca x CoCuO 5+δ -based single-cells increase from 1.47 to 2.04 W cm−2 (800 °C) while the output current density retentions rise from 82.2 to 94.7 % after 100 h (700 °C and 0.7 V). This guides the design of robust double perovskite catalysts in solid oxide cells, metal-air batteries, photocatalysis, and oxygen sensors. [ABSTRACT FROM AUTHOR]