An efficient approach to characterize pseudo-merohedral twins by precession electron diffraction: Application to the LaGaO3 perovskite

Hexagonal Si-Ge Class of Semiconducting Alloys Prepared by Using Pressure and Temperature

Multi-anvil and laser-heated diamond anvil methods have been used to subject Ge and Si mixtures to pressures and temperatures of between 12 and 17 GPa and 1500-1800 K, respectively. Synchrotron angle dispersive X-ray diffraction, precession electron diffraction and chemical analysis using electron microscopy, reveal recovery at ambient pressure of hexagonal Ge-Si solid solutions (P6₃ /mmc). Taken together, the multi-anvil and diamond anvil results reveal that hexagonal solid solutions can be prepared for all Ge-Si compositions. This hexagonal class of solid solutions constitutes a significant expansion of the bulk Ge-Si solid solution family, and is of interest for optoelectronic applications.

Creating Reactivity with Unstable Endmembers using Pressure and Temperature: Synthesis of Bulk Cubic Mg0.4 Fe0.6 N

Alloy and nitride solid solutions are prominent for structural, energy and information processing applications. There are frequently however barriers to making them. We remove barriers to reactivity here using pressure with a new synthetic approach. We target pressures where the reasons for cubic endmember nitride instability can become the driving force for cubic nitride solid solution stability. Using this approach we form a novel rocksalt Mg0.4 Fe0.6 N solid solution at between 15 and 23 GPa and up to 2500 K. This is a system where, neither an alloy nor a nitride solid solution form at ambient conditions and bulk MgN and FeN endmembers do not form, either at ambient or at high pressure. The new nitride is formed, by removing endmember lattice mismatch with pressure, allowing a stabilizing redistribution of valence electrons upon heating. This approach can be employed for a range of normally unreactive systems. Mg, Fe and enhanced nitrogen presence, may also indicate a richer reaction chemistry in our planets interior.

Dense Si(x)Ge(1-x) (0 < x < 1) materials landscape using extreme conditions and precession electron diffraction

High-pressure and -temperature experiments on Ge and Si mixtures to 17 GPa and 1500 K allow us to obtain extended Ge-Si solid solutions with cubic (Ia3) and tetragonal (P4(3)2(1)2) crystal symmetries at ambient pressure. The cubic modification can be obtained with up to 77 atom % Ge and the tetragonal modification for Ge concentrations above that. Together with Hume-Rothery criteria, melting point convergence is employed here as a favored attribute for solid solution formation. These compositionally tunable alloys are of growing interest for advanced transport and optoelectronic applications. Furthermore, the work illustrates the significance of employing precession electron diffraction for mapping new materials landscapes resulting from tailored high-pressure and -temperature syntheses.

Electron diffraction characterization of a new metastable Al2Cu phase in an Al–Cu friction stir weld

The space group of a new metastable orthorhombic Al2Cu phase, located in the Al-rich interfacial region of an Al–Cu friction stir weld, was unambiguously identified asIc2mby a recently developed systematic method combining precession electron diffraction and convergent-beam electron diffraction. This metastable phase has the same tetragonal lattice as its stable θ-Al2Cu counterpart (tetragonal,I4/mcm, No. 140). The tetragonal-to-orthorhombic symmetry lowering is due to slight modifications of the atomic positions in the unit cell. This metastable phase can be transformed into the stable θ-Al2Cu phase byin situirradiation within the transmission electron microscope.

Structure of the new mineral sarrabusite, Pb5CuCl4(SeO3)4, solved by manual electron-diffraction tomography

The new mineral sarrabusite Pb5CuCl4(SeO3)4 has been discovered in the Sardinian mine of Baccu Locci, near Villaputzu. It occurs as small lemon–yellow spherical aggregates of tabular crystals (< 10 µm) of less than 100 µm in diameter. The crystal structure has been solved from and refined against electron diffraction of a microcrystal. Data sets have been measured by both a manual and an automated version of the new electron-diffraction tomography technique combined with the precession of the electron beam. The sarrabusite structure is monoclinic and consists of (010) layers of straight chains formed by alternating edge-sharing CuO4Cl2 and PbO8 polyhedra parallel to the c axis, which share corners laterally with two zigzag corner-sharing chains of PbO6Cl2 and PbO4Cl4 bicapped trigonal prisms. These blocks are linked together by SeO_3^{2-} flat-pyramidal groups.