Speaker
Description
Monika Všianská$^{1}$, Iva Rambousková$^{1}$, Aneta Benešová$^{1}$, Jana Pavlů$^{1}$* and Mojmír Šob$^{1,2}$
$^{1}$ Department of Chemistry, Faculty of Science, Masaryk University, Kamenice 753/5,
CZ-625 00 Brno, Czech Republic
$^{2}$ Institute of Physics of Materials CAS, v. v. i., Žižkova 513/22,
CZ-616 00 Brno, Czech Republic
An ab initio analysis of MoSi$_2$-XSi$_2$ (X = Nb, Ta, Ti) disilicide nanocomposites was performed, where the most stable configurations of non-diffusive phase boundaries were determined as follows: MoSi$_2$(AC)/TiSi$_2$(DACB), MoSi$_2$(AD)/TiSi$_2$(CADB), MoSi$_2$(AC)/Nb(Ta)Si$_2$(BAC), MoSi$_2$(AB)/ Nb(Ta)Si$_2$(CAB) and MoSi$_2$(AB)/Nb(Ta)Si$_2$(ABC), where A, B, C and D denote the configurations of most densely occupied crystal planes. In the case of MoSi$_2$(AC)/TiSi$_2$(DACB), MoSi$_2$(AC)/TiSi$_2$(BDAC) and MoSi$_2$(AC)/Nb(Ta)Si$_2$(BAC) interfaces, the influence of defects on structure properties was studied. It was found that all structures containing the defects are stable with respect to the standard element reference states despite their destabilisation effect. This was not always true when pure disilicides were used as reference states. Furthermore, the most preferred positions of vacancies, divacancies, Al and Si impurities and vacancy-impurity couples were determined together with their formation energies. However, it was necessary to be careful during the studies of vacancies as some of them may undergo recombination with interstitial impurities, as it happened in the systems with Si impurities. The destabilisation effect of vacancies can be reduced by the presence of impurities, which leads to the conclusion that the impurities can facilitate the formation of vacancies. The diffusion (exchange of Mo-X atoms across the phase boundary) caused the stabilisation of studied structures by creating a diffusive interface in some cases.
The ab initio calculations were performed using the VASP code (Vienna Ab initio Simulation Package), employing the Density Functional Theory with Projector Augmented Wave method. The exchange-correlation energy was evaluated within the Local Density Approximation with the Ceperley-Alder functional.
Acknowledgement: Computational resources were supplied by the project “e-Infrastruktura CZ” (e INFRA CZ LM2018140 and e-INFRA CZ (ID:90140)) supported by the Ministry of Education, Youth and Sports of the Czech Republic. Further, the Academy of Sciences of the Czech Republic (Institutional Project No. RVO:68081723) is acknowledged.
