• Ohuchi, Fumio S.
• Dandeneau, Christopher
• Bordia, Rajendra K.
• Yang, Yihsun

Abstract

<jats:p>Electron transport mechanisms in reduced Sr0.5Ba0.5Nb2O6 (SBN50) are investigated from ∼100 to 955 K through an analysis of the electrical conductivity (σ) and the Seebeck coefficient (S) with respect to temperature (T). Notably, experimental evidence is presented that supports a scenario of Anderson localization below 600 K and carrier excitation across a mobility edge at higher temperature. As a relaxor ferroelectric, stoichiometric SBN has intrinsic disorder associated with both the distribution of Sr/Ba vacancies and the formation of polarized nanoregions. The removal of oxygen through reduction generates conduction electrons in SBN. At the lowest temperatures measured (100–155 K), the electrical conductivity exhibits a temperature dependence characteristic of variable range hopping, followed by a transition to small polaron hopping at intermediate temperatures (250–545 K). In both the variable range and small polaron hopping regimes, a semiconductor-like temperature dependence of the electrical conductivity (dσ/dT &amp;gt; 0) was observed. However, above 615 K, dσ/dT decreases dramatically and eventually becomes metal-like (dσ/dT &amp;lt; 0). Concomitantly, the Seebeck coefficient exhibits a linear dependence on lnT from 615 to 955 K with the same slope (∼104 μ V/K) for both polycrystalline SBN50 and single crystalline SBN61 (both reduced), indicating a similar, constant density of states near the Fermi level for both compositions. The application of Seebeck coefficient theory to this inherently disordered material reveals that the excitation of carriers across a mobility edge is likely responsible for the change in dσ/dT at high temperature. Such findings may have a significant impact in the field of conductive ferroelectrics.</jats:p>

Topics

• density
• impedance spectroscopy
• mobility
• theory
• Oxygen
• semiconductor
• Strontium
• electrical conductivity
• Barium