A transferable force field for CdS-CdSe-PbS-PbSe solid systems

Unexpected origin of magnetism in monoclinic Nb12O29 from first-principles calculations

Nb12O29 is a 4d transition metal oxide that occurs in two forms with different symmetries, monoclinic (m) and orthorhombic (o). The monoclinic form has unusual magnetic properties; below a temperature of 12 K, it exhibits both metallic conductivity and antiferromagnetic ordering. Here, first-principles density-functional theory calculations are...

Structural tale of two novel (Cr,Mn)C carbides in steel

Chromium (Cr), Manganese (Mn), and Carbon (C) are well known alloying elements used in technologically important alloy steels and advanced high strength steels. It is known that binary CrCx and MnCx carbides can be formed in steels, but in this study we reveal for the first time that Cr and Mn were found combined in novel ternary cementite type ...

Atomic Resolution Monitoring of Cation Exchange in CdSe-PbSe Heteronanocrystals during Epitaxial Solid?Solid?Vapor Growth

Here, we show a novel solid?solid?vapor (SSV) growth mechanism whereby epitaxial growth of heterogeneous semiconductor nanowires takes place by evaporation-induced cation exchange. During heating of PbSe-CdSe nanodumbbells inside a transmission electron microscope (TEM), we observed that PbSe nanocrystals grew epitaxially at the expense of CdSe...

Structural and magnetic properties of NiCx and NiNx (x=0 to 1/3) solid solutions from first-principles calculations

First-principles calculations have been performed for a variety of Ni3X (X = C, N) phases, as well as for NiXy (y = 0 to 1/3) solid solutions to clarify the persistent controversy regarding its magnetic state. The calculations show that the solid solution phases based on hexagonal-close-packed (hcp or ?-) Ni have relatively high stability for X...

Novel ultrafine Fe(C) precipitates strengthen transformation-induced-plasticity steel

A transmission electron microscopy study was conducted on nanoprecipitates formed in Ti microalloyed transformation-inducedplasticity-assisted steels, revealing the presence of Ti(N), Ti2CS and a novel type of ultra-fine Fe(C) precipitate. The matrix/precipitate orientation relationships, sizes and shapes were investigated in detail. The...

Stability and crystal structures of iron carbides: A comparison between the semi-empirical modified embedded atom method and quantum-mechanical DFT calculations

Iron carbides play a crucial role in steel manufacturing and processing and to a large extent determine the physical properties of steel products. The modified embedded atom method (MEAM) in combination with Lee's Fe-C potential is a good candidate for molecular dynamics simulations on larger Fe-C systems. Here, we investigate the stability and...

Characterization of NbC and (Nb, Ti)N nanoprecipitates in TRIP assisted multiphase steels

Multiphase steels utilising composite strengthening may be further strengthened via grain refinement or precipitation by the addition of microalloying elements. In this study a Nb microalloyed steel comprising martensite, bainite and retained austenite has been studied. By means of transmission electron microscopy (TEM), we have investigated the...

Role of carbon and nitrogen in Fe2C and Fe2N from first-principles calculations

Although Fe2C and Fe2N are technologically important materials, the exact nature of the chemical bonding of C and N atoms and the related impact on the electronic properties are at present unclear. Here, results of first-principles electronic structure calculations for Fe2X (X = C, N) phases are presented. The electronic structure calculations...

Origin of Predominance of Cementite among Iron Carbides in Steel at Elevated Temperature

A long-standing challenge in physics is to understand why cementite is the predominant carbide in steel. Here we show that the prevalent formation of cementite can be explained only by considering its stability at elevated temperature. A systematic highly accurate quantum mechanical study was conducted on the stability of binary iron carbides....

Structural, electronic, and magnetic properties of iron carbide Fe7C3 phases from first-principles theory

The iron carbide Fe7C3 exhibits two types of basic crystal structures, an orthorhombic (o-) form and a hexagonal (h-) one. First-principles calculations have been performed for the basic Fe7C3 forms and for the related ?-Fe3C cementite phase. Accurate total-energy calculations show that the stability of Fe7C3 is comparable to that of ?-Fe3C. The...