Complex oxide systems are promising candidates for materials in solid oxide fuel cells, oxygen sensors, and other applications requiring oxygen anion diffusion. [1][2][3] In particular, mixed mode conductors such as the manganite oxides are of interest as cathode materials for solid oxide fuel cells. [3][4][5] One interesting property of some complex oxides is their ability to form distinct, oxygen-defi cient ordered phases with high ionic conductivity. [ 1 , 6-8 ] Here, we report the discovery, using in situ synchrotron-based X-ray techniques, of a new method for creating oxygen vacancy ordered phases in epitaxial manganite thin fi lms. The method involves depositing an oxygen defi cient complex oxide fi lm on top of a stoichiometric manganite fi lm to act as an oxygen getter. Once the getter layer exceeds a critical thickness, a phase transition to an oxygen vacancy ordered superlattice occurs in the manganite fi lm. We demonstrate the use of oxygen defi cient SrTiO 3-δ (STO) and LaAlO 3-δ (LAO) as getter layers and superlattice formation in four manganite systems: La 0.7 Sr 0.3 MnO 3 (LSMO), Pr 0.7 Ca 0.3 MnO 3 (PCMO), La 0.7 Ca 0.3 MnO 3 (LCMO), and LaMnO 3 (LMO). The superlattices may be maintained at ambient conditions after cooling to room temperature. This growth technique constitutes a new procedure for preparing such structures, and may lead to the discovery of new, technologically diverse phases of complex oxide materials that cannot be grown by traditional deposition techniques.Refl ection high energy electron diffraction (RHEED) and X-ray scattering are commonly employed to monitor thin fi lm thickness, roughness, morphology, and structure during deposition. [ 9 -14 ] The penetrating power of X-rays makes them uniquely suited for structural studies of the buried layers in heterostructures. To monitor fi lm thickness during deposition, the intensity at "anti-Bragg" positions may be monitored in real time. [15][16][17] During homoepitaxial layer-by-layer growth, this intensity oscillates with the period corresponding to the deposition of 1 unit cell, hereafter referred to as a monolayer (ML). For heteroepitaxial growth, the anti-Bragg intensity oscillates with a period of either 1 or 2 MLs, depending on the details of the system. [ 17 , 18 ] Here, we use this method by measuring the intensity of specularly refl ected X-rays at the (0 1 2 0) position on the crystal truncation rod of the substrate ([010] is the surface normal).The Anti-Bragg intensity measured during pulsed laser deposition (PLD) of a LSMO/STO/LAO heterostructure on SrTiO 3 010 is shown in Figure 1 a . The oscillations during the LSMO deposition are shown in green, and the time between Figure 1 . a) Anti-Bragg intenisty oscillations for the deposition of a LSMO/STO/LAO heterostructure. The large intensity increase during the LAO deposition is the result of a Bragg peak forming due to oxygen vacancy ordering in the buried LSMO fi lm. b) The post deposition X-ray refl ectivity.

Articles you may be interested inThe effect of stress on the dielectric and tunable properties of barium stannate titanate thin films Appl. Phys. Lett. 94, 052902 (2009); 10.1063/1.3073743 Barium titanate nanocrystals and nanocrystal thin films: Synthesis, ferroelectricity, and dielectric properties J. Appl. Phys. 100, 034316 (2006); 10.1063/1.2218765 Combined effect of thickness and stress on ferroelectric behavior of thin BaTiO 3 films J. Appl. Phys. 93, 2855 (2003); 10.1063/1.1540225Diffuse phase transitions, electrical conduction, and low temperature dielectric properties of sol-gel derived ferroelectric barium titanate thin films Pyroelectric Ba 0.8 Sr 0.2 TiO 3 thin films derived from a 0.05 M solution precursor by sol-gel processing Scaling effects in polycrystalline ferroelectric thin films were investigated by preparing barium titanate in a manner that maintained constant composition and film thickness while allowing systematically increased grain size and crystalline coherence. The average grain dimensions ranged from 60 to 110 nm, and temperature dependence of permittivity analysis revealed diffuse phase transitions in all cases. Maximum permittivity values ranged from 380 to 2040 for the smallest to largest sizes, respectively. Dielectric hysteresis is evident at room temperature for all materials, indicating stability of the ferroelectric phase. Comparison of permittivity values at high electric fields indicates that the intrinsic dielectric response is identical and microstructural artifacts likely have a minimal influence on film properties across the sample series. Permittivity values, however, are substantially smaller than those reported for bulk material with similar grain dimensions. X-ray line broadening measurements were taken for the grain size series at the Cornell High Energy Synchrotron Source ͑CHESS͒, which revealed coherent scattering dimensions substantially smaller than the microscopy-determined grain size. Collectively these data sets suggest that permittivity values are influenced not only by grain size but also by the mosaic structure existing within each grain, and that thin film thermal budgets, which are several hundred degrees lower than used for bulk processing, are responsible for reduced crystalline coherence, and likely the origin of degraded electromechanical response in thin film ferroelectrics.

A new diffractometer system was designed and built for the G2 experimental station at the Cornell High Energy Synchrotron Source (CHESS). A six-circle κ goniometer, which provides better access to reciprocal space compared to Eulerian cradles, was chosen primarily to perform large angle Bragg diffraction on samples with preferred crystallographic orientations, and can access both horizontal and vertical diffraction planes. A new atmosphere- and temperature-controlled sample stage was designed for thin film thermomechanical experiments. The stage can be operated in ultrahigh vacuum and uses a Be dome x-ray window to provide access to all scattering vectors above a sample’s horizon. A novel design minimizes sample displacements during thermal cycling to less than 160μm over 900°C and the stage is motorized for easy height adjustments, which can be used to compensate for displacements from thermal expansion. A new area detector was built and a new line detector was purchased. Both detectors cover a large region in reciprocal space, providing the ability to measure time-resolved phenomena. A detailed description of the design and technical characteristics is given. Some capabilities of the diffractometer system are illustrated by a strain analysis on a thin metal film and characterization of organic thin films with grazing incidence diffraction. The G2 experimental station, as part of CHESS, is a national user facility and is available to external users by application.

International Journal of Fracture (2005) 136:265-284Abstract. The companion article proposed a model for radial crack development at sharp contacts. The major extension of this model from previous works is the inclusion of a 'wedging' mechanism, to form a three-stress-field description of indentation crack evolution. Here, the amplitude terms of the three stress-intensity factors comprising the model are calibrated from experimental in situ and post situ inert-environment radial crack measurements on soda-lime glass. These values are scaled to predict radial crack evolution during cube corner and Vickers indentation of fused silica and soda lime glass in inert and ambient air environments. Both the conventional two-field and the proposed threefield model predictions are compared with radial crack lengths measured during indentation loadunload cycles (through the transparent materials with an in-situ apparatus). The three-field model is shown to be a great improvement over the two-field model in the description of crack evolution at cube-corner indentations, particularly with respect to the significant crack extension during loading and the attainment of a maximum crack length during unloading. The three-field model is consistent with observations of Vickers fracture in soda-lime glass and is able to reproduce the features of radial fracture evolution on the 'anomalous' glass, fused silica.

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