Abstract
The relativistic Doppler effect of Mössbauer γ‐quanta from a 57Co source is investigated in the resonance absorption of FeS2 powder and in the resonance scattering from the (200) reflection of FeS2 single crystals in the temperature range 298 K ≦ T ≦ 598 K. The shift of resonances is d ln ω/dT = −(2.58 ± 0.07) × 10−15 K−1, while the quadrupole splitting dEQ = (633 ± 9) μm/s is temperature independent. Single crystal data exhibit an unexpected additional broadening of one quadrupole resonance, which originates in an interference of nuclear resonance and electronic Rayleigh scattering.