H. Euchner

The impact of nitrogen content and vacancies on structure and mechanical properties of Mo–N thin films

Based on a combined computational and experimental study, we show that besides the thermodynamically stable β-MoN0.5 and δ2-MoN phases, also metastable γ-MoNx and its ordered relative γ′-MoNx can be synthesized by physical vapor deposition. The formation of the NaCl-based γ-MoNx phase is favored for nitrogen concentrations between 23 and 34 at.% (i.e., xu2009=u20090.30–0.53). Higher nitrogen contents (close to the 3:2 stoichiometry, hence, MoN0.67) favor the ordering of the vacancies at the nitrogen sublattice (hence, γ′-MoNx). The highest hardness of ∼33u2009GPa is obtained for single-phase cubic-structured γ-MoN0.53 coatings, whereas the ordered γ′-MoN0.67 coatings are slightly softer with a hardness of ∼28u2009GPa.

Direct measurement of individual phonon lifetimes in the clathrate compound Ba 7.81 Ge 40.67 Au 5.33

Engineering lattice thermal conductivity requires to control the heat carried by atomic vibration waves, the phonons. The key parameter for quantifying it is the phonon lifetime, limiting the travelling distance, whose determination is however at the limits of instrumental capabilities. Here, we show the achievement of a direct quantitative measurement of phonon lifetimes in a single crystal of the clathrate Ba7.81Ge40.67Au5.33, renowned for its puzzling ‘glass-like’ thermal conductivity. Surprisingly, thermal transport is dominated by acoustic phonons with long lifetimes, travelling over distances of 10 to 100u2009nm as their wave-vector goes from 0.3 to 0.1u2009Å−1. Considering only low-energy acoustic phonons, and their observed lifetime, leads to a calculated thermal conductivity very close to the experimental one. Our results challenge the current picture of thermal transport in clathrates, underlining the inability of state-of-the-art simulations to reproduce the experimental data, thus representing a crucial experimental input for theoretical developments.Phonon lifetime is a fundamental parameter of thermal transport however its determination is challenging. Using inelastic neutron scattering and the neutron resonant spin-echo technique, Lory et al. determine the acoustic phonon lifetime in a single crystal of clathrate Ba7.81Ge40.67Au5.33.

Atomic structure and phason modes of the Sc–Zn icosahedral quasicrystal

The detailed atomic structure of the binary icosahedral ScZn7.33 quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering.

Atomic structure and phason modes of the Sc-Zn icosahedral quasicrystal

The detailed atomic structure of the binary icosahedrali-ScZn7.33 quasicrystal has been investigated by means ofhigh-resolution synchrotron single-crystal Xraydiffraction and absolute scale measure ...

Diffuse scattering and phason modes in the Zn–Sc binary icosahedral quasicrystal

Recently, a new binary icosahedral quasicrystal Zn-Sc has been obtained by Canfield et. al. [1]. Because of the chemical order and the x-ray contrast between Zn and Sc, this phase is a nice system ...

Diffuse scattering in the Zn6Sc 1/1 cubic approximant

The low-temperature phase transition of the Zn6Sc cubic 1/1 approximant [1] has been investigated by X-ray diffraction. It is a crystalline approximant to a recently discovered quasicrystal Zn88Sc1 ...