In situ Raman spectroscopic studies of FeS2 pyrite up to 675 K and 2100 MPa using a hydrothermal diamond anvil cell

摘要

Raman scattering experiments of natural FeS2 pyrite were performed at simultaneous high-pressure and high-temperature conditions up to 675 K and 2100 MPa using a hydrothermal diamond anvil cell combined with micro-Raman spectroscopy. Four out of five Raman active modes [E-g, A(g), T-g(1) and T-g(3)] were resolved at ambient conditions, the remaining T-g(2) [similar to 377 cm(-1)] mode was weak and unresolved occurring similar to 2 cm(-1) from the intense A(g) [379 cm(-1)] mode. The frequency shifts of the Eg [343 cm(-1)] and A(g) [379 cm(-1)] modes were determined to be quadratic functions of pressure and temperature: nu(343) = 343.35 - 0.0178x Delta T - 8.4E-6x(Delta T)(2) + 0.00367x Delta p - 3.7E-7x(Delta p)(2) + 1.0E-6x Delta Tx Delta p and nu(379) = 379.35 - 0.0295x Delta T - 9.0E-66(Delta T)(2) + 0.00460x Delta p - 5.3E-7x(Delta p)(2) + 7.0E-76DTx Delta p. The positive pressure dependence of both modes indicates stress-induced contraction of S-S and Fe-S bonds, whereas the negative temperature dependence shows temperature-induced expansion of them. The Raman spectra of pyrite were used to derive its bulk modulus at high temperatures, thermal expansion coefficient at high pressures and anharmonic parameters at high-pressure and high-temperature conditions.