The microstructure and stoichiometry of pyrite FeS_2−x

Abstract

Both natural and synthetic crystals of pyrite, FeS2−x, have been analyzed chemically and examined structurally by transmission electron microscopy and x-ray powder diffraction. Chemical analysis and density measurements have shown the synthetic crystals, grown at 850 K, are frequently deficient in sulfur, with a composition of FeS2−x with x ⋚ 0.15. From a refinement of the pyrite structure using the integral intensities of the x-ray powder pattern, a variation in the sulfur population parameter was obtained ranging from 0.87(2) to 1.03(3). A correlation according to Vegard's rule between the population factor and the lattice parameter a0 has been proven. Transmission electron microscope examination revealed that the crystals did not contain a significant population of disorder defects which may account for this apparent sulfur deficit. Therefore the nonstoichiometry in pyrite has to be interpreted in terms of S vacancies which can be understood as the tendency of the material to reduce the high anion content in the unit cell. The structural nature of nonstoichiometric pyrite is discussed in relationship to other related disulfides.

CIBS Solar Cell Development Final Scientific/Technical Report

“…Figure 23 shows the optical absorption spectrum for this thin film sulfurized at 450 o C for 1 hr. The film processed at 450 °C had an apparent bandgap of 0.94 eV that is in agreement with the literature [18].…”

“…The band gap energy determined form the Tauc measurement ( Figure 28) was 0.93 eV, which is just slightly below the expected value of 0.95 eV [18].…”

“…The very high absorption coefficient, α = 6 x 10 5 cm -1 for λ = 633 nm [16] and the composition of abundant, cheap and non-toxic elements makes pyrite an interesting material for thin-film solar cells [17]. Iron disulfide has a bandgap energy of E g = 0.95 eV, [18] somewhat less than the ideal. However, a thorough modeling of the potential of pyrite indicates that efficiencies of 20% are possible [19].…”

Thin Film Solar Cells Using Earth-Abundant Materials

“…This value of V oc is lower than the theoretical value of about 500 mV [106]. The low photopotential is attributed to the strong pinning of the Fermi level caused by surface states [105] as well as bulk defects caused by the sulphur deficiency [107].…”

Estudo do comportamento eletroquímico de eletrodos de FeS₂ em meio ácido

“…da pirita [79,88]; por exemplo , amostras de pirita sintética deficientes de enxofre , da ordem de 7,5 %, tem-se mostrado promissoras para o uso de coletores solares [79] .…”