Room-temperature Raman scattering measurements were carried out on well-characterized samples of MgB2-xCx. The Raman line corresponding to the E2g phonon mode shows progressive hardening from 620/cm in pristine MgB2 to 775/cm in the sample with a C fraction of x = 0.2. The corresponding line-width on the other hand increased from a value of about 220 to 286/cm in samples with x = 0.1, beyond which it decreased to a value of 167/cm for x = 0.2. From the average mode frequency and the line width obtained from Raman measurements and taking the values of N(0) obtained from the calculated variation in σ-hole density of states in MgB2-xCx, the electron–phonon coupling strength to the E2g phonon, λ2g, was evaluated using Allen’s formula. This remained large for low C fraction, but exhibited a rapid decrease for x > 0.10. Using this value of λ2g appropriately weighted, TC was obtained from McMillan’s equation. These values were in good agreement with the measured TC variation in MgB2-xCx.

Raman Scattering Investigation of Electron–Phonon Coupling in Carbon Substituted MgB2. T.Sakuntala, A.Bharathi, S.K.Deb, N.Gayathri, C.S.Sundar, Y.Hariharan: Journal of Physics - Condensed Matter, 2005, 17, 3285-92