Christian Roucau

α-Bi4V2O10 crystal structure and oxidation mechanism. X-ray and electron diffraction analysis

The {alpha}-Bi{sub 4}V{sub 2}O{sub 10} structure was determined from Rietveld analysis of X-ray diffraction powder data and electron diffraction microscopy. {alpha}-Bi{sub 4}V{sub 2}O{sub 10} crystallizes in the orthorhombic system, space group Pnma with a = 5.4704(2) {angstrom}, b = 17.2471(4) {angstrom}, and c = 14.9219(4) {angstrom}. This compound, derived from the Aurivillius family, presents a typical layered structure of alternating (Bi{sub 2}O{sub 2}){sub 2n} and (VO{sub 3}){sub 2n} layers. These layers are built up by corner-sharing VO{sub 5} square pyramids in the succession along [010] of three pyramids pointing alternately up and down. Structural relationships between this compound and Bi{sub 4}V{sub 2}O{sub 10.66} are described, and a structural mechanism that might explain the oxidation at room temperature of {alpha}-Bi{sub 4}V{sub 2}O{sub 10} into Bi{sub 4}V{sub 2}O{sub 10.66} is proposed.

Microstructure of (Bi,Pb)-Sr-Ca-Cu-O fibres: Study by electron microscopy

Abstract We report on the microstructure of (Bi,Pb)-Sr-Ca-Cu-O superconducting fibres grown by the laser floating zone (LFZ) method and studied by means of scanning (SEM) and transmission (TEM) electron microscopy. The shape, size and orientation of the grains in the LFZ fibre are analysed. Electron diffraction patterns display the low T c (≈80 K) 2212 phase for almost all grains. The presence of CuO precipitates and the distribution of Pb within the grains, and within the amorphous intergranullar material, has been established by wavelength dispersive spectroscopy (on SEM) and energy dispersive spectroscopy (on TEM). Two modulations, q 1 =δ 1 b ∗ +c ∗ and q 2 =δ 2 b ∗ , as well as indications of intermodulation, have been observed within the grains in both diffraction patterns and images.

HREM study of the epitaxial growth of Fe on Ir(001)

Abstract High resolution transmission electron microscopy is used to study the structural evolution of Fe thin films deposited by MBE onto fcc Ir(001) in Fe Ir superlattices with various Fe and Ir thicknesses. For very thin Fe layers, the Ir Fe interfaces are coherent and the body centered tetragonal (bct) structure of iron (up to 5 atomic planes) is evidenced with a tetragonality ratio c a = 1.36 . For thicker iron layers, Fe remains in its bct structure in the vicinity of the Ir Fe interface but relaxes to its usual bcc structure a few planes far from it.

Cross-sectional TEM investigations of the microstructure and film-substrate substrate interface in Y-Ba-Cu-O thin films

Abstract Superconducting YBaCuO films deposited on yttria-stabilized zirconia (YSZ) and SrTiO 3 substrates have been studied by transmission electron microscopy. The films were elaborated by RF diode sputtering, the annealing procedure being performed ex-situ, at temperatures close to 900°C. Characterization by X-ray diffraction and resistivity measurements shows that the films mainly consist of the desired 123 phase. The c -axis perpendicular orientation has been obtained whatever the substrate orientation with YSZ and with (100) oriented SrTiO 3 . We report here the results of the cross-sectional TEM investigations of the microstructures and film/substrate interfaces. The presence of a 300 nm thick intermediate layer in films deposited on YSZ is reported while HREM studies clearly show the epitaxial growth of the 123 phase on SrTiO 3 (100).

Conductive and superconductive materials derived from dmit-complexes

Recent results on the synthesis, structure and properties of conductive and superconductive materials derived from the transition metal complexes [M(dmit)2]n- are described.

The high Tc superconductor Bi2Sr2CaCu2O8 studied by electron microscopy. Influence of the partial substitution of Yb for Ca on the modulated structure

The incommensurate modulation of high-Tc superconductors of the type Bi2Sr2Ca1−yYbyCu2O8+x is characterised by electron diffraction. The results are in favour of an atomic displacive one-dimensional modulation with both transverse and longitudinal components. In a four-dimensional description of the modulated structure, the reflection conditions that are evidenced obey the relation: h+l+m=2n. The partial substitution of Yb cations for Ca proves to affect the electrical properties of these materials. Analysis of compounds having different Yb contents (0≤y≤0.66) reveals that the modulation wave vector decreases with increasing y until y=0.5.

Ferroelastic behaviour of the (Ln)Ba2Cu3O6+x orthorhombic phase

Abstract The orthorhombic phase of the high Tc superconductor (Ln)Ba2Cu3O6+A is observed in transmission electron microscopy. This phase is ferroelastic and exhibits two different orientation domains. A full description of the twin boundaries is given. The behaviour of the ferroelastic domains at the intersection of orthogonal twin walls is more particularly investigated.

The role of Microstructure, Nanostructure and Composition in the Brilliant Red Slip of Roman Terra Sigillata Pottery from Southern Gaul

Terra sigillata pottery is the most famous fine ware of the Roman period and is characterised by the red colour of the body (or paste) and slip (or gloss). The term derives from its colour, which is similar to the reddish colour of clay (terra), and the frequent use of stamps or moulds (sigilla). Its great success was due to its remarkable gloss, also called slip, which provides a bright, deep red appearance. Electron energy loss spectroscopy in a transmission electron microscope (TEM-EELS) and x-ray diffraction (XRD) techniques were used for analysing the sub-microscopic structure of the material. The paper describes the analyses made on five shard samples from two important workshops in southern Gaul. These samples appear to have the same slip structure, consisting in sub-microscopic hematite and corundum crystals in a glass matrix. The colour of hematite depends on crystal size. The largest crystals have a black colour, while the red colour occurs when the crystals decrease to submicron size. The off-white or light-yellow corundum crystals could be acting as a brightener. -- ICCROM

TEM Analysis Of Advanced Devices For Electronics Or Spintronics: From Structure To Properties

During the last decades, transmission electron microscopy has become an essential tool for solving problems involving microstructural questions in materials science. Its unique ability to provide direct imaging of particular regions of the material together with structural information made it highly valuable in the study of complex materials including domains as ferroelastic or ferroelectric materials. Moreover, TEM is the dedicated technique for studying defects (dislocations, boundaries, precipitates, interfaces) which can either affect or enhance the desired properties (mechanical, optical or magnetic properties, transport). After a brief review of typical answers given by TEM on materials questions, we discuss the interest of the technique to investigate new devices for energy, communication or security applications. We show in particular that new developments in TEM now allow us to determine various fields in the specimens, in particular strain or magnetic fields, which bring direct information on the physical properties.

Strain Accommodation and Relaxation Mechanisms in Epitaxially Grown Manganites

Epitaxial growth of La 1-x (SrorCa) x MnO 3 manganites (LSMO or LCMO) has been successfully achieved on SrTiO 3 (001) and MgO(001) substrates. We report the influence of the deposition conditions, in particular growth rate, annealing and nature of the substrate, on the state of strain in the manganite layers. Fully strained layers are reported at very slow growth rate on SrTiO 3 substrates while misfit dislocations are clearly observed in layers grown on MgO and alsoin layers grown on SrTiO 3 , after annealing at high temperature. Besides, evidence is given for a rhombohedral (respectively orthorhombic) distortion relaxation in LSMO (respectively LCMO) layers. The microstructure of the manganite layers is analyzed taking into account their non-isomorphic growth on the cubic substrates.