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A. Hannemann

Publications and source records attributed to A. Hannemann.

4 recordsLinked to original sources

Non-equilbrium Dynamics in Amorphous Si_3B_3N_7

We present extensive numerical investigations of the structural relaxation dynamics of a realistic model of the amorphous high-temperature ceramic a-Si$_3$B$_3$N$_7$, probing the mean square displacement (MSD) of the atoms, the bond survival probability (BSP), the average energy, the specific heat, and the two-point energy average. Combining the information from these different sources, we identify a transition temperature $T_c \approx 2000$ K below which the system is no longer ergodic and physical quantities observed over a time $t_{obs}$ show a systematic parametric dependence on the waiting time $t_w$, or age, elapsed after the quench. The aging dynamics 'stiffens' as the system becomes older, which is similar to the behavior of highly idealized models such as Ising spin-glasses and Lennard-Jones glasses.

cond-mat.stat-mech

Non-equilibrium dynamics in amorphous Si3B3N7

We present numerical investigations of the dynamics on the energy landscape of a realistic model of the high-temperature ceramic a-Si3B3N7. Below a critical temperature Tc = 2000 K, the system is no longer in equilibrium, and we predict that the material has a glass transition in this temperature range at high pressure. Analyzing the two-time energy correlation function shows aging in this system, which is linked to the geometrical properties of the energy landscape.

cond-mat.stat-mech

Modelling of Si-B-N ceramics

We present results of computer simulations of amorphous Si3B3N7 ceramics. The computed pair correlation functions are in agreement with the experimental results. Regarding the structural properties of the B-N, Si-N and N-Si/B coordination spheres, our results are in full agreement with experimental data. We confirm that silicon is tetrahedrally coordinated by nitrogen, and boron is trigonally planar coordinated by nitrogen. Furthermore we find that the coordination of nitrogen by the cations is also trigonally planar. Additionally our results suggest that a significant structural property of these materials is a heterogenity on a lengthscale of about 0.5nm. The simulation of relaxation and annealing processes of this new substance indicate the existence of rather stable BN3 building units, while the SiN4 building units are comparatively malleable.

cond-mat.mtrl-sci