Interface structure and defects in directionally solidified oxide–oxide eutectic composites

International audienceInterfaces in ternary oxide-oxide eutectic composites prepared by directional solidification are investigated at the atomic scale. Two systems are studied that both display a chinese script interconnected microstructure, associating three monocrystalline phases, alumina (A), yttrium aluminium garnet (Y) phase or a perovskite phase SmAlO 3 (S), and zirconia (Z), i.e. Al 2 O 3-Y 3 Al 5 O 12-ZrO 2 (A-Y-Z) or Al 2 O 3-SmAlO 3-ZrO 2 (A-S-Z). Most interfaces are semicoherent. The curved interfaces between A and Z nodules are strongly faceted and parallel to dense planes of both crystals or to dense planes of alumina. The same features occur for AS interfaces, which show longer facets. The steps between facets accommodate the misfits. Y-A and Y-Z interfaces are often parallel to a dense plane of one crystal owing to a slight deviation of the Y phase from the perfect orientation relationship (OR). The OR between Y and A phases found in binary eutectic is modified by the presence of Z. Similarly, although the same OR occurs between A and Z in binary and ternary eutectics with the Y phase, this OR is modified by the presence of S. The discussion emphasizes the predominant role of interfacial order on the final orientation relationships

Evidence of extended defects in pure zirconia irradiated by swift heavy ions

X-ray diffraction, transmission electron microscopy, and optical spectroscopy were used to investigate the microstructure of polycrystalline samples of pure monoclinic zirconia irradiated by high energy ions. These techniques point out the existence of extended defects and they allow to monitor the tetragonal to monoclinic phase transition as a function of the temperature during isochronal annealings. The Landau theory approach explains the phase transition mechanism via the presence of an important strain field induced by dislocations. Though high and low energy ions can effectively stabilize the same tetragonal phase in the irradiated layer, only point defects are produced at low energy whereas extended defects are also observed at high energy, showing the strong influence of the energy deposition modes on the observed microstructures

The structure of low temperature crystallized LiCoO2

International audienc

Femtosecond Laser-Induced Crystallization in Glasses: Growth Dynamics for Orientable Nanostructure and Nanocrystallization

International audienc

Heterogeneity and Disorder in Ti1-xFeyO2-d Nanocrystal Rutile-Based Flowerlike Aggregates: Detection of Anatase

Here we report results of systematic investigation of heterogeneity and disorder in Ti1-xFeyO2-d nanorod rutile-based flowerlike aggregates. It was found that Ti1-xFeyO2-d aggregates are composed of two crystalline phases: rutile as a dominant and anatase as a minor phase. Flowerlike aggregates were found to grow from an isometric core ca. 5-10 nm in diameter that was built from anatase and rutile nanorods ca. 5 x 100 nm that were grown on the anatase surface having base plane (001) intergrowth with an anatase plane. The direction of rutile nanorods growth, i.e., direction of the nanorod elongation, was [001]. Highly nonisometric rutile crystals produce anisotropic X-ray powder diffraction line broadening and doubling of vibrational bands in Raman spectra. Both these techniques confirmed nonisometric character of rutile crystals and gave a quantitative measure of crystal shape anisotropy in excellent agreement with high-resolution transmission electron microscopy measurements. In addition, from the atomic pair distribution function and Raman spectral analyses the level of vacancy concentration was determined in rutile and anatase phases of investigated samples

Intricate disorder in defect fluorite/pyrochlore: a concord of chemistry and crystallography

International audienceIntuitively scientists accept that order can emerge from disorder and a significant amount of effort has been devoted over many years to demonstrate this. In metallic alloys and oxides, disorder at the atomic scale is the result of occupation at equivalent atomic positions by different atoms which leads to the material exhibiting a fully random or modulated scattering pattern. This arrangement has a substantial influence on the material's properties, for example ionic conductivity. However it is generally accepted that oxides, such as defect fluorite as used for nuclear waste immobilization matrices and fuel cells, are the result of disorder at the atomic scale. To investigate how order at the atomic scale induces disorder at a larger scale length, we have applied different techniques to study the atomic composition of a homogeneous La$^2$ Zr$^2$ O$^7$ pyrochlore, a textbook example of such a structure. Here we demonstrate that a pyrochlore, which is considered to be defect fluorite, is the result of intricate disorder due to a random distribution of fully ordered nano-domains. Our investigation provides new insight into the order disorder transformations in complex materials with regards to domain formation, resulting in a concord of chemistry with crystallography illustrating that order can induce disorder