Carbon-doping was found to increase the upper critical field HC2 in superconducting MgB2 thin-film and bulk samples. However, the C effects on both HC2 and lattice parameters were very different between thin films and bulk, suggesting C might incorporate differently in the two cases. This work combines ab initio calculations and thin-film lattice parameter measurements in order to explore the connection between substitutional and interstitial C in MgB2 and experimental bulk and thin-film lattice parameters.

Impact of Substitutional and Interstitial Carbon Defects on Lattice Parameters in MgB2. A.K.Bengtson, C.W.Bark, J.Giencke, W.Dai, X.Xi, C.B.Eom, D.Morgan: Journal of Applied Physics, 2010, 107[2], 023902