Advantageous power factor anomaly in Mn1.68-XCu.6+X+Y+ZCo.24-YNi.48-ZO4 thin films
J.G. Moyer, D.A. Kukuruznyak, F.S. Ohuchi
Department of Materials Science and Engineering, University of Washington, Box 352120, Seattle, WA 98195, USA
Compositional variations are made to a reference composition Mn1.68-XCu.6+X+Y+ZCo.24-YNi.48-ZO4, and the thermopower and electrical conductivity are measured to examine changes in the power factor terms. Properties are determined for thin films obtained through Metal Organic Decomposition processing. This low-temperature fabrication route allows retention of meta-stable Mn4+ and Cu1+ ions, which are essential to the n-type materialís electronic behavior. Compositional variations modify the oxidation states of Mn and Cu. and in turn, the conductivity and thermopower values. Charge balance models are used to interpret the influences of doping. The data indicates that replacing portions of Co with Cu raises both the conductivity and thermopower magnitude, and exchanging small amounts of Mn or Ni with Cu reduces these thermoelectric factors. Surprisingly, the effects of doping show parallel rises or declines in conductivity and thermopower magnitude. Inconsistencies with standard conductivity models are identified. This factor is more strongly impacted by carrier mobility than by the number of charge carriers in these materials. The changes in mobility are attributed to variations in the ionic environment. While thermopower varies by as much as 30%, there is a 400% alteration in conductivity as a result of doping.