LaCoO 3 and La 0.8 Ca 0.2 CoO 3 ceramics show a nonelastic stress-strain behavior during four-point bending experiments where hysteresis loops are observed during loading-unloading cycles. Permanent strain is stored in the material after unloading, and a mechanism related to ferroelastic domain switching in the rhombohedral perovskite is proposed. Domain switching in the materials has been confirmed using X-ray diffractometry. Fracture toughnesses of La 0.8 Ca 0.2 CoO 3 measured using single-edge notched beam and single-edge V-notched beam methods coincide and are equal to 2.2 MPa⅐m 1/2 at room temperature and decrease to ϳ1 MPa⅐m 1/2 at temperatures >300°C. A decrease in fracture toughness is consistent with ferroelastic behavior, because the rhombohedral distortion decreases with increasing temperature.

Single-photon emitting point defects in semiconductors have emerged as strong candidates for future quantum technology devices. In the present work, we exploit crystalline particles to investigate relevant defect localizations, emission shifting and waveguiding. Specifically, emission from 6H-SiC micro-and nanoparticles ranging from 100 nm to 5 μm in size is collected using cathodoluminescence (CL), and we monitor signals attributed to the Si vacancy (VSi) as a function of its location. Clear shifts in the emission wavelength are found for emitters localized in the particle center and at the edges. By comparing spatial CL maps with strain analysis carried out in transmission electron microscopy, we attribute the emission shifts to compressive strain of 2-3% along the particle a-direction. Thus, embedding VSi qubit defects within SiC nanoparticles offers an interesting and versatile opportunity to tune single-photon emission energies, while simultaneously ensuring ease of addressability via a self-assembled SiC nanoparticle matrix.

Work, 13(2),

Many heat resistant ferritic steels have superior thermal expansion and conductivity properties compared to Ni-based alloys but are somewhat limited in their applications above ~600 o C by their mechanical properties. Efforts are being made to use precipitation strengthening to improve these properties and thus the efficiency of such alloys [1]. One such effort uses coherent (Ni,Fe)Al precipitates in a ferritic matrix, Fig. 1, and has shown good initial results. Transmission electron microscopy (TEM) has been used to understand globally the precipitate microstructure as it evolves with heat treatment. In order to understand the mechanisms by which such precipitation occurs, it is important to know how the composition variations in the structure on the scale of the precipitates evolve with heat treatment. Atom probe tomography (APT) [2] excels at such atomicscale characterization and is a strong complement to the imaging capabilities of TEM. The local electrode atom probe (LEAP) [3] has been used to characterize the nanoscale microstructure in this alloy in order to determine the chemistry of the third phase (yellow arrow) precipitated inside the (Ni,Fe)Al B2 phase, which is shown as the darkly-imaging phase in Fig. 1b. The Fe-18.1at.% Ni-22.9at.% Al-9.5at.% Cr alloy was produced by vacuum induction melting followed by solution annealing at 1200°C with air cooling. For atom probe analysis, rods of this material were sharpened by electropolishing to have a radius of curvature of less than 100 nm at the apex. Three phases in the microstructure were identified consistent with prior work [1]. A primary Fe-rich phase (A2), a secondary NiAl phase (B2), and a third Fe-rich precipitate. Precipitates of the primary phase within the secondary phase were not seen to form within ~15 nm of large scale primary regions, i.e., there is a denuded zone or precipitate free zone near the primary phase A2 phase. Fig. 2 shows a LEAP analysis with a volume of (80x80x500) nm made up of 110 million atoms. On the right side of Fig. 2, two composition profiles are shown. The top one is across a narrow B2 region between two A2 regions showing the ~50/50 composition of the NiAl phase in this region. The lower profile reveals that the very small (~5nm) precipitates (yellow arrow in Fig. 1) inside the NiAl phase appear to be secondary Fe-rich phase. Through this correlative microscopy effort with TEM and APT, a greater understanding of the precipitation sequence and evolution of the microstructure is obtained.

No abstract