AVS 50th International Symposium
    Electronic Materials and Devices Wednesday Sessions
       Session EM-WeM

Paper EM-WeM4
Unusual Behavior of Electrical Conductivity and Thermopower Found in Mn@sub 1.68-X@Cu@sub .6+X+Y+Z@Co@sub .24-Y@Ni@sub .48-Z@O@sub 4@ Thin Films

Wednesday, November 5, 2003, 9:20 am, Room 321/322

Session: Multifunctional Electronic Materials
Presenter: F.S. Ohuchi, University of Washington
Authors: F.S. Ohuchi, University of Washington
J.G. Moyer, University of Washington
D.A. Kukuruznyak, University of Washington
M.S. Prowse, University of Washington
Correspondent: Click to Email
The thermopower, S, and electrical conductivity, @sigma@, are measured on variations of a reference composition, Mn@sub 1.68-X@Cu@sub .6+X+Y+Z@Co@sub .24-Y@Ni@sub .48-Z@O@sub 4@. Doped compositions show parallel increases or decreases in conductivity and thermopower magnitude unlike typical band-gap conducting materials. This is desirable for increasing the efficiency parameter called the power factor, S@super 2@@sigma@, for thermoelectric applications. While thermopower varies by as much as 30%, the conductivity changes by up to a factor of four in the compositions explored. Conduction is attributed to small polaron hopping between neighboring Mn ions. Thin films are obtained through Metal Organic Decomposition processing. This is a low-temperature fabrication route that allows for the retention of meta-stable Mn@super 4+@ and Cu@super 1+@ ions that are essential to favorable electronic behavior. Compositional variations modify the Mn@super 3+@, Mn@super 4+@, Cu@super 1+@, and Cu@super 2+@ concentrations, and in turn change the conductivity and thermopower. Supplemental XPS work defines changes in Cu oxidation states and oxygen content, and thermopower data provides Mn oxidation state information. Using the Heikes and Nernst-Einstein transport models we explain the seemingly incongruent behavior in thermopower and conductivity and identify that the discrepancy occurs in the conductivity factor. The nature of the unusual conduction behavior will be discussed.