Recent studies by a number of research groups have shown that the structure of epitaxial BiFeO3 (BFO) films changes drastically as a function of substrate-induced biaxial compression, with the crystal structure changing from one being nearly rhombohedral (R-like) to one being nearly tetragonal (T-like), where the “T-like” structure is characterized by a highly enhanced c/a ratio of out-of-plane c to in-plane a lattice parameters. In this work, we show that the critical compressive strain σc necessary to induce this transition can be reduced significantly by substituting 10% Ba for Bi [Bi0.9Ba0.1FeO3−δ (BBFO)] and that the “T-like” phase in both BBFO and BFO is stable up to the decomposition temperatures of the films in air. Furthermore, our results show that the BBFO solid solution shows clear ferromagnetic properties in contrast to its undoped BFO counterpart.

The annular dark field (ADF) image contrast of a 0.92% tensile strained GaN0.045As0.955 layer on GaAs substrate was studied with a scanning transmission electron microscope (STEM) as a function of ADF detector inner semi-angles ranging from 28 mrad to 90 mrad. The GaN0.045As0.955 layers were brighter than the surrounding GaAs for the values of ADF detector semiangle up to 65 mrad, and the measured contrast decreased with increasing ADF detector inner semi-angle. For a 37 nm thick specimen, the GaN0.045As0.955 intensity is about 13% higher than that of GaAs in the 28 mrad ADF detector inner semi-angle. Multislice simulations show that the displacement around substitutional N atoms plays an important role in the observed ADF-STEM contrast, while the contribution to the contrast due to misfit strain between GaN0.045As0.955 and GaAs is small.

The nanostructures self-organized via lateral composition modulation in 140 period (InAs)13/(GaSb)13 superlattices grown by molecular beam epitaxy have been studied by highresolution x-ray diffraction and infrared absorption. Three samples were analyzed in this study; two with lateral composition modulation and one without. X-ray reciprocal space map scans were taken to determine the average morphology of the modulated structures. Both vertical and lateral satellite peaks were observed for the samples with composition modulation, indicating the formation of two-dimensional nanowire arrays. The vertical wavelength measured for the two samples was twice the period intended by the growers. This is due to the face-centered cubic type stacking of the nanowires. Infrared absorption spectra of these two samples were compared to the spectra of the sample with no lateral composition modulation. Transitions involving the heavy- and light-hole bands in the GaSb hole quantum well and the electron subbands of the InAs electron quantum well were not evident for the samples with lateral composition modulation, indicating that the nanostructure of the lateral composition modulation affects the optical response of the sample, which is important for optoelectronic device applications.

The copper alloys commonly referred to as nickel aluminum bronzes (NAB) are widely used in marine applications due to their excellent seawater corrosion resistance and good mechanical properties. Unfortunately, these alloys are susceptible to a variety of surface sensitive degradation processes such as cavitation and wear which significantly reduce service life. Laser surface melting and cladding techniques have recently demonstrated a potential to substantially enhance the performance of NAB components. This is associated with the occurrence of a martensitic or Widmanstätten transformation from the high temperature bcc β phase accompanied by precipitation of ordered intermetallic particles collectively referred to as κ. Optimization of these techniques requires an improved understanding of the evolution of microstructure in the NAB system under conditions of rapid solidification, however little data is currently available. In this paper, transmission electron microscopy is used to examine the microstructures of a series of laser surface melted NAB alloys containing from 8 to 12 wt. % Al, 3.8 to 6.5 wt. % Ni, 3.8 to 6.5 wt. % Fe, ∽1 wt. % Mn and, in some cases, lesser amounts of Ti or Zr.

Although the unusual microstructural and electronic properties of charge density wave (CDW) modulated compounds have been extensively investigated over the past two decades, many aspects of the complex behaviour of these systems remain unexplained. As a result, the characterization of a new family of CDW structures, in which the CDW properties can be widely varied in a predictable manner, is of experimental and theoretical interest.

The Nb3X4 (X = S, Se, Te) family of compounds is based on a hexagonal unit cell built up of edge and face sharing NbX6 octahedra (Figure 1). The structure is characterized by zigzag Nb-Nb chains and large hexagonal tunnels running parallel to the c-axis. One member of this family, Nb3Te4, is known to undergo a CDW phase transition at ∼100 K. A large number of metal atoms can be introduced into the tunnels to form a family of isostructural, intercalated compounds AyNb3X4. Electrical resistivity measurements on polycrystalline pellets of InyNb3X4 (X = Se, Te) have revealed temperature anomalies indicative of the formation of CDW in these materials.

Improvements in instrumentation for energy-dispersive X-ray microanalysis (EDX) and electron energy-loss spectroscopy (EELS) have underlined the need for suitable standards for measuring performance. We report the results from several laboratories that were supplied with a test specimen consisting of a thin film of nickel oxide supported on a molybdenum grid. The Ni-Kα/Mo-Kα count ratio was used as an indication of number of stray electrons and/or X-rays in the TEM column; the Ni-Kα peak/background ratio provided a measure of the total background in the EDX spectrum, including bremsstrahlung contributions and the effect of detector electronics. By providing values typical of current instrumentation, the results illustrate how the test specimen can be used to evaluate TEM/EDX systems prior to purchase, during installation, and (periodically) during operation. The NiO films were also used to test EELS acquisition and quantification procedures: measured Ni/O elemental ratios were all within 10% of stoichiometry.

The effects of transition metal dopants on superconductivity in samples of nominal composition Bi2CaSr2(Cu1-xMx)208+δ with M = Co, Fe, Ni and Zn have been investigated for 0 ≤ x ≤ 1. Co and Fe additions progressively suppress the ? of the doped material and result in semiconducting behaviour for x ≤ 0.2. In the ranges 0 ≤ x ≤ .07 and near x = 1.0, x-ray diffraction reveals the samples are essentially single phase but are multiphase otherwise. Ni and Zn dopants have only a very slight effect on Tc; however, EDX analysis reveals these elements are not significantly Incorporated into the superconducting phase.