ChemInform Abstract: Electrical Properties of Pure and Titanium‐Doped Hematite Single Crystals, in the Basal Plane, at Low Oxygen Pressure.

Abstract

022ChemInform Abstract The electrical conductivity of α-Fe2O3 and TixFe2-xO3 (0.03 < x < 0.05) is measured as a function of oxygen pressure at temp. in the range 200-900 rc C. The transport properties of hematite are discussed in terms of the small polaron model.

Electrical transport properties of Ti-doped Fe2O3(0001) epitaxial films

“…These activation energies agree remarkably well with the 0.11 eV calculated by ab initio theory, 13 as well as 0.1 eV estimated for hematite basal plane conduction given by Goodenough et al, 11 and 0.08 eV from Gharibi et al. 12 Thus, conductivity from 300 to 140 K for all Ti concentrations is consistent with small polaron hopping and an activation barrier of ~0.1 eV. For temperatures well below Θ D /2, the small polaron hopping probability rapidly decreases and the polaron hopping model no longer applies, 36 as seen in the inset for Fig.…”

“…10 A hopping barrier of ~0.1 eV within the ab-plane has emerged from several theoretical and experimental studies. [11][12][13] Crystallographic anisotropies in the conductivity have also been observed and attributed to spin flip scattering, which lowers the conductivity for transport along the c axis. 13,14 Although progress has been made on the theoretical front, experimental studies of transport in hematite have been limited due to difficulties resulting from the generally high resistivity of hematite and ambiguities associated with measurements on polycrystalline samples.…”

Synthesis, electronic transport and optical properties of Si:α-Fe2O3 single crystals

“…Ubiquitous in nature, bulk charge transport in hematite also plays an important role in many geochemical processes. 10,11 Electronic transport agrees well with the small-polaron model 12,13 but a thorough analysis in this framework around room temperature -where PEC cells would operate -has not been performed. Recent work by our group utilized conductivity, Seebeck and Hall effect measurements as functions of temperature to probe the nature of small polarons in single crystals of another promising photoelectrode: tungstendoped bismuth vanadate (W:BiVO 4 ).…”

“…This is plausible, as SiO 2 can be transported at temperatures greater than 900 1C using various halogens, 24 but is at odds with several reports in the literature using identical or similar synthesis conditions, who reported insulating (resistivity 410 5 O cm) undoped a-Fe 2 O 3 . 13,36,37 As silica is ever-present in these syntheses, we do not understand this discrepancy at present. Interestingly, when Ti metal was added to the reaction vessel, only trace quantities (o20 ppm) were present in the crystals, indicating very inefficient Ti-incorporation by this method.…”

“…Good agreement with the small-polaron model was observed from 140 to 300 K. The Hall effect was analyzed using the conventional semiconductor framework, yielding a Hall mobility of B10 À1 cm 2 V À1 s À1 that was temperature independent from 190 to 290 K. Additionally, Gharibi et al measured the conductivity and Seebeck coefficient of single crystals of Ti:a-Fe 2 O 3 at elevated temperatures and concluded that small-polaron hopping was in the non-adiabatic regime at 780 K. 13 However, this assignment is questionable, as the non-adiabatic regime requires a transfer integral that is too small for most real materials. 19 In both of these prior reports the conductivity and either the Seebeck or Hall effect were measured as functions of temperature.…”