Jörg von Appen

A density-functional study of the phase diagram of cementite-type (Fe,Mn)3C at absolute zero temperature.

The phase diagram of (Fe1−x Mnx)3C has been investigated by means of density‐functional theory (DFT) calculations at absolute zero temperature. The atomic distributions of the metal atoms are not random‐like as previously proposed but we find three different, ordered regions within the phase range. The key role is played by the 8d metal site which forms, as a function of the composition, differing magnetic layers, and these dominate the physical properties. We calculated the magnetic moments, the volumes, the enthalpies of mixing and formation of 13 different compositions and explain the changes of the macroscopic properties with changes in the electronic and magnetic structures by means of bonding analyses using the Crystal Orbital Hamilton Population (COHP) technique.

Impact of Mn on the solution enthalpy of hydrogen in austenitic Fe-Mn alloys: A first-principles study

Hydrogen interstitials in austenitic Fe‐Mn alloys were studied using density‐functional theory to gain insights into the mechanisms of hydrogen embrittlement in high‐strength Mn steels. The investigations reveal that H atoms at octahedral interstitial sites prefer a local environment containing Mn atoms rather than Fe atoms. This phenomenon is closely examined combining total energy calculations and crystal orbital Hamilton population analysis. Contributions from various electronic phenomena such as elastic, chemical, and magnetic effects are characterized. The primary reason for the environmental preference is a volumetric effect, which causes a linear dependence on the number of nearest‐neighbour Mn atoms. A secondary electronic/magnetic effect explains the deviations from this linearity.

Synthesis, High-resolution Crystal Structure Refinement and Magnetic Properties of the Manganese-rich Cementite-type Mn1.8Fe1.2C

The manganese-rich ternary cementite phase Mn1.8Fe1.2C has been synthesized by a ceramic route in an almost quantitative yield, and the crystal structure refinement on the basis of high-resolution X-ray powder diffraction data using MoKα1 radiation has been performed. The carbon atom is found in a slightly distorted trigonal prism composed of Mn and Fe atoms, with a rather narrow bond length range from 1.95 to 2.09 Å . The magnetic susceptibility data clearly indicate long-range ordering phenomena, in particular dominant antiferromagnetic interactions, as predicted by density-functional theory. Graphical Abstract Synthesis, High-resolution Crystal Structure Refinement and Magnetic Properties of the Manganese-rich Cementite-type Mn1.8Fe1.2C