Band or Polaron: The Hole Conduction Mechanism in the p-Type Spinel Rh 2ZnO4

Arpun R. Nagaraja, Nicola H. Perry, Thomas O. Mason, Yang Tang, Matthew Grayson, Tula R. Paudel, Stephan Lany, Alex Zunger

Research output: Contribution to journalArticlepeer-review

49 Scopus Citations


Given the emerging role of oxide spinels as hole conductors, we discuss in this article the traditional vs. new methodologies of determining the type of conduction mechanism at play - localized polaronic vs. band-like transport. Applying (i) traditional small polaron analysis to our in-situ high temperature four-point conductivity and thermopower measurements, we previously found an activated mobility, which is indicative of the small polaron mechanism. However, (ii) employing the recent developments in correcting density functional methodologies for hole localization, we predict that the self-trapped hole is unstable and that Rh 2ZnO 4 is instead a band conductor with a large effective mass. The hole mobility measured by high-field room temperature Hall effect also suggests band rather than polaron conduction. The apparent contradiction between the conclusion of the traditional procedure (i) and first-principles theory (ii) is resolved by taking into account in the previous transport analysis the temperature dependence of the effective density of states, which leads to the result that the mobility is actually temperature-independent in Rh 2ZnO 4. Our case study on Rh 2ZnO 4 illustrates the range of experimental and theoretical approaches at hand to determine whether the transport mechanism of a semiconductor is band or small polaron conduction.

Original languageAmerican English
Pages (from-to)269-274
Number of pages6
JournalJournal of the American Ceramic Society
Issue number1
StatePublished - Jan 2012

NREL Publication Number

  • NREL/JA-5900-54346


  • photovoltaics
  • semiconductor
  • solar energy
  • transparent conductors


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