Precession Electron Diffraction - a versatile tool for the characterization of Phase Change Materials

Towards 3D crystal orientation reconstruction using automated crystal orientation mapping transmission electron microscopy (ACOM-TEM)

To relate the internal structure of a volume (crystallite and phase boundaries) to properties (electrical, magnetic, mechanical, thermal), a full 3D reconstruction in combination with in situ testing is desirable. In situ testing allows the crystallographic changes in a material to be followed by tracking and comparing the individual crystals and phases. Standard transmission electron microscopy (TEM) delivers a projection image through the 3D volume of an electron-transparent TEM sample lamella. Only with the help of a dedicated TEM tomography sample holder is an accurate 3D reconstruction of the TEM lamella currently possible. 2D crystal orientation mapping has become a standard method for crystal orientation and phase determination while 3D crystal orientation mapping have been reported only a few times. The combination of in situ testing with 3D crystal orientation mapping remains a challenge in terms of stability and accuracy. Here, we outline a method to 3D reconstruct the crystal orientation from a superimposed diffraction pattern of overlapping crystals without sample tilt. Avoiding the typically required tilt series for 3D reconstruction enables not only faster in situ tests but also opens the possibility for more stable and more accurate in situ mechanical testing. The approach laid out here should serve as an inspiration for further research and does not make a claim to be complete.

Inorganic Double Helices in Semiconducting SnIP

SnIP is the first atomic-scale double helical semiconductor featuring a 1.86 eV bandgap, high structural and mechanical flexibility, and reasonable thermal stability up to 600 K. It is accessible on a gram scale and consists of a racemic mixture of right- and left-handed double helices composed by [SnI] and [P] helices. SnIP nanorods <20 nm in diameter can be accessed mechanically and chemically within minutes.

Martensite adaption through epitaxial nano transition layers in TiNiCu shape memory alloys

Titanium-rich TiNiCu shape memory thin films with ultralow fatigue have been analysed for their structural features by transmission electron microscopy. The stabilization of austenite (B2) and orthorhombic martensite (B19) variants epitaxially connected to Ti2Cu-type precipitates has been observed and found responsible for the supreme mechanical cycling capability of these compounds. Comprehensiveex situandin situcooling/heating experiments have demonstrated the presence of an austenitic nanoscale region in between B19 and Ti2Cu, in which the structure shows a gradual transition from B19 to B2 which is then coupled to the Ti2Cu precipitate. It is proposed that this residual and epitaxial austenite acts as a template for the temperature-induced B2↔B19 phase transition and is also responsible for the high repeatability of the stress-induced transformation. This scenario poses an antithesis to residual martensite found in common high-fatigue shape memory alloys.

Thermoelectric efficiency of (1 − x)(GeTe) x(Bi2Se0.2Te2.8) and implementation into highly performing thermoelectric power generators

First report of high performance thermoelectric generator based on GeTe substituted with Bi and Se yielding the composition of (1 − x)(GeTe) x(Bi₂Se_0.2Te_2.8).

Superposition twinning supported by texture in ZnO nanospikes

The morphology and real structure of wurtzite-type ZnO nanospikes grown by the recently introduced flame transport synthesis have been examined by means of advanced transmission electron microscopy (TEM). The rapid synthesis produces nanospikes showing a well defined texture which restricts TEM experiments to a preferred viewing direction of [2 {\overline 1}{\overline 1}3]. Forced by the specific morphology, all of the observed nanospikes show a complicated superposition of twinned domains as an intrinsic real structural feature. The high-resolution contrasts are characterized by lamellar fringes parallel to the (1 {\overline 1} 0 {\overline 1}) planes, and the quasi-kinematic diffraction patterns contain satellite peaks based on multiple scattering. All these phenomena can be interpreted by comparison of experimental and simulated data relying on a supercell approach.

New insights into hard phases of CoCrMo metal-on-metal hip replacements

The microstructural and mechanical properties of the hard phases in CoCrMo prosthetic alloys in both cast and wrought conditions were examined using transmission electron microscopy and nanoindentation. Besides the known carbides of M(23)C(6)-type (M=Cr, Mo, Co) and M(6)C-type which are formed by either eutectic solidification or precipitation, a new mixed-phase hard constituent has been found in the cast alloys, which is composed of ∼100 nm fine grains. The nanosized grains were identified to be mostly of M(23)C(6) type using nano-beam precession electron diffraction, and the chemical composition varied from grain to grain being either Cr- or Co-rich. In contrast, the carbides within the wrought alloy having the same M(23)C(6) structure were homogeneous, which can be attributed to the repeated heating and deformation steps. Nanoindentation measurements showed that the hardness of the hard phase mixture in the cast specimen was ∼15.7 GPa, while the M(23)C(6) carbides in the wrought alloy were twice as hard (∼30.7 GPa). The origin of the nanostructured hard phase mixture was found to be related to slow cooling during casting. Mixed hard phases were produced at a cooling rate of 0.2 °C/s, whereas single phase carbides were formed at a cooling rate of 50 °C/s. This is consistent with sluggish kinetics and rationalizes different and partly conflicting microstructural results in the literature, and could be a source of variations in the performance of prosthetic devices in-vivo.