Stress-strain response of GaN-ML at different temperatures in the range of 10 to 1700 K at a strain rate of 0.89%/ps. The linear behavior indicates the elastic nature, except for the higher temperatures. A zig-zag type of variation of the response at higher temperatures is shown in the inset. This indicates the transition to ductile nature at higher temperatures.
The fracture process at 700 K and 1300 K. The values in the parentheses are the critical stress (in GPa) and strain (in%), respectively, at that particular instant of fracture time. At 700 K, the fracture occurs with a clear cut, indicating the brittle nature while at 1300 K which is close to TBDT for this strain rate, the formation of a group of atoms as a chain that links the separated portions can be seen. The negative values of corresponding stresses represent the compression of the group of atoms due to higher temperature.
The variation of critical stress with temperature is shown. The critical stress decreases linearly with increasing temperature, in confirmation with the prediction of Eq. (4) . For comparison, the curves are obtained with the GaN-ML having single and double vacancies. All the three cases exhibit the similar qualitative behavior, although there are quantitative differences. A reduction in the critical stress of the GaN-ML in the presence of atomic vacancies is also evident. In all the three cases, a kink can be observed at higher temperatures, indicating the brittle to ductile transition.
(a) The variation of as a function of inverse temperature at a strain rate of 0.89%/ps. The temperature at which an abrupt change in the slope of the curve occurs corresponds to TBDT . The occurrence of change of slopes at high temperatures is shown in the inset. The results are compared for GaN-ML with single and diatomic vacancies. It can also be seen that TBDT falls nearly at the same point in all the three cases, as the fraction of vacant atoms in the GaN-ML is much lesser as compared to the total number of atoms in the GaN-ML; (b) the variation of as a function of inverse temperature at strain rates of 0.1, 0.4, 0.89, 1.6, and 2.5%/ps. The corresponding values of TBDT are obtained, as shown in Table I ; (c) variation of vs. . The value of TBDT shifts to the higher values with the increase in rate of applied tensile loading. The linear dependency is consistent with the prediction of Eq. (10) .
The variation of thermal conductivity of GaN-ML in the temperature range of 300 to 2000 K. A rapid reduction in thermal conductivity that saturates at higher temperatures can be seen. At higher temperatures, the increased phonon-phonon interactions and the inelastic boundary scattering reduce the mean free paths. The results are compared with the (25,0) nanotube generated from the same GaN-ML.
TBDT (in K) at various strain rates (in%/ps).
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