Measurements were made of the microwave surface impedance of a powder sample and of 2 films. The powder sample had TC = 39K and the films had TC = 29 and 38K. These samples exhibited different temperature dependences of the field penetration depth. Over a period of six months, the film with TC = 38K degraded to a TC of 35K.

The Microwave Surface Impedance of MgB2 Thin Films. A.J.Purnell, A.A.Zhukov, T.Nurgaliev, G.Lamura, Y.Bugoslavsky, Z.Lockman, J.L.MacManus-Driscoll, H.Y.Zhai, H.M.Christen, M.P.Paranthaman, D.H.Lowndes, M.H.Jo, M.G.Blamire, L.Hao, J.C.Gallop, L.F.Cohen: Superconductor Science and Technology, 2003, 16, 1-6