A hydrated crystalline calcium carbonate phase: Calcium carbonate hemihydrate
As one of the most abundant materials in the world, calcium carbonate, CaCO3, is the main constituent of the skeletons and shells of various marine organisms. It is used in cement industry and plays a crucial role in the global carbon cycle and formation of sedimentary rocks. For more than a century, only three polymorphs of pure CaCO3—calcite, aragonite, and vaterite—were known to exist at ambient conditions, as well as two hydrated crystal phases, monohydrocalcite (CaCO3·1H2O) and ikaite (CaCO3·6H2O). A hitherto unknown monoclinic nano crystalline phase, hemihydrate CaCO3·½H2O, was solved based on automated diffraction tomography (ADT) data.
A high-strength silicide phase in a stainless steel alloy designed for wear-resistant applications
Hardfacing alloys provide strong, wear-resistant and corrosion-resistant coatings for extreme environments such as those within nuclear reactors. Here, we report an ultra-high-strength Fe–Cr–Ni silicide phase, named π-ferrosilicide, within a hardfacing Fe-based alloy (2.5 times harder than the surrounding austenite and ferrite phases). Electron diffraction tomography (EDT) has allowed the determination of the atomic structure of this phase.
Ab initio structure determination and quantitative disorder analysis on nanoparticles by electron diffraction tomography
Small particle size, various types of disorder and intergrown structures render the description of many structures at atomic level by standard crystallographic methods difficult. Here a proof-of-principle study, the characterization of the strongly disordered zeolite beta structure using a combination of electron exit-wave reconstruction, automated diffraction tomography (ADT), crystal disorder modelling and electron diffraction simulations is reported. The crystal structures of two intergrown Zeolite Beta polymorphs BEA and BEB were solved from a single automated diffraction tomography (ADT) data set by direct methods. The ratio for BEA/BEB = 48:52 was determined by analysis of the diffuse scattering extracted from the reconstructed intensity space based on ADT data and comparison with simulated electron diffraction data.