Abstract
A first-principle computational method has been used to investigate the effects of Ru dopants on the electronic and optical absorption properties of marcasite FeS2. In addition, we have also revealed a new marcasite phase in RuS2, unlike most studied pyrite structures. The new phase has fulfilled all the necessary criteria of structural stability and its practical existence. The transition pressure of 8 GPa drives the structural change from pyrite to orthorhombic phase in RuS2. From the thermodynamical calculation, we have reported the stability of new-phase under various ranges of applied pressure and temperature. Further, from the results of phonon dispersion calculated at Zero Point Energy, pyrite structure exhibits ground state stability and the marcasite phase has all modes of frequencies positive. The newly proposed phase is a semiconductor with a band gap comparable to its pyrite counterpart but vary in optical absorption by around 106 cm−1. The various Ru doped structures have also shown similar optical absorption spectra in the same order of magnitude. We have used crystal field theory to explain high optical absorption which is due to the involvement of different electronic states in formation of electronic and optical band gaps. Lӧwdin charge analysis is used over the customarily Mulliken charges to predict 89% of covalence in the compound. Our results indicate the importance of new phase to enhance the efficiency of photovoltaic materials for practical applications.
Highlights
A first-principle computational method has been used to investigate the effects of Ru dopants on the electronic and optical absorption properties of marcasite FeS2
We report first principle investigations based on Kohn–Sham density functional theory (DFT)[22,23], where the total energy is expressed in terms of electron density rather than the wave function
To further investigate the choice of exchange correlation potential on the result sensitivity, the modified Becke Johnson potential is used for calculations, where the potential depends on the kinetic energy density
Summary
A first-principle computational method has been used to investigate the effects of Ru dopants on the electronic and optical absorption properties of marcasite FeS2. Of RuS2 with energy band gap (1.3 eV) close to its pyrite phase and shows high optical absorption coefficient (106 cm−1) outperforming R uS2 thin films, silicon and even direct gap materials such as GaAs. The orthorhombic structure of the compound was obtained by introducing new energy levels in the forbidden gap of parent m-FeS2 through Ru doping in Fe site. The same has been confirmed from experiment with enhanced band gap of the pyrite p hase[21] This shows that Ru acts as an effective dopant, many studies avoid extending the idea in understanding the effects in marcasite structure, indicating the approach to be problematic. Our results question the literature regarding the low photovoltaic performance in marcasite phase and reveal the coexistence of m-and p-phase of R uS2 that may motivate the experimentalist for further verification
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