Dresden 2003 – wissenschaftliches Programm

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DF: Dielektrische Festkörper

DF 4: Gl
äser Ib (gemeinsam FV DF/DY)

DF 4.3: Vortrag

Dienstag, 25. März 2003, 10:45–11:00, HSZ/403

Thermodynamic properties of the Si/B/N-system - a computer simulation study. — •Alexander Hannemann, J. Christian Schön, and Martin Jansen — MPI f. Festkörperforschung, Heisenbergstr. 1, 70569 Stuttgart

We present results on the thermodynamic properties of the Si₃B₃N₇ system. Extensive NVT MC-simulations at many different volumes and temperatures show that the system should possess a critical temperature T_crit ≈ 3700 K and a critical pressure of p_crit≈ 0.7 GPa. At elevated pressures (≈ 5 GPa) our results suggest that the sytem undergoes an ergodic to non-ergodic transition at a glass transition temperature T_G≈ 2000 K. In the non-ergodic regime the system is amorphous.

Experimentally the amorphous Si₃B₃N₇ system has an unusually low density of ≈ 1.9 g/cm³, compared to the weighted sum of the crystalline binary phases h-BN and β− Si₃N₄ (≈ 2.8 g/cm³). One possible explanation is the existence of nanovoids. We investigated the stability of voids of various sizes by NpT-MC-simulation for large systems. For temperatures T<T_G, voids are stable on the time scale of our NpT-MC simulation, while for temperatures T>T_G these voids are destroyed.