Electronic Transport Characterization of BiVO 4 Using AC Field Hall Technique
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Electronic Transport Characterization of BiVO4 Using AC Field Hall Technique Jeffery Lindemuth1, Alexander J. E. Rettie2, Luke G. Marshall4, Jianshi Zhou4, and C. Buddie Mullins2,3,4 1 Lake Shore Cryotronics, Westerville Ohio 43082 (USA) 2 McKetta Department of Chemical Engineering, The University of Texas at Austin, TX 78712 (USA) 3 Center for Electrochemistry, Department of Chemistry and Biochemistry, The University of Texas at Austin, TX 78712 (USA) 4 Materials Science and Engineering Program, Texas Materials Institute, Department of Mechanical Engineering, The University of Texas at Austin, TX 78712 (USA) ABSTRACT Bismuth vanadate (BiVO4) is a photoelectrode for the oxidation of water. It is of fundamental importance to understand the electrical and photoelectrochemical properties of this material. In metal oxides, the electronic transport is described by the small polaron model, first described by Mott. In this model, the resistivity varies with temperature as ߩሺܶሻ ݁ܶ ןሺாೌȀሺಳ்ሻሻ, where Ea is the hopping activation energy, kB is the Boltzmann constant and T is the absolute temperature. Resistivity measurements confirm that small polaron hopping dominates in temperature ranges from 250 K to 300 K. In addition measurements from 175K to 250K show the variable range hopping dominates the transport. To this end, the electronic transport properties of BiVO4 single crystal were characterized using resistivity measurements and Hall effect measurements over temperatures ranging from 175 K to 300 K. INTRODUCTION A promising method for storing solar energy is to directly produce hydrogen gas by using photoelectrochemical (PEC) cell. The PEC cell will directly split water into hydrogen and oxygen. [1,2] The choice of the photoelectrode is critical to the performance of the PEC cell. An ideal photoelectrode is a stable material composed of abundant elements. The photoelectrode should have good light absorption and high quality charge transport properties. Metal oxides, such as titania (TiO2) [3], hematite (Į-Fe2O3) [4] and tungsten oxide (WO3) [5] have been used as photoelectrodes. Complex metal oxides, such as BiVO4, are now of interest. Increased efficiencies using photoelectrodes of polycrystalline BiVO4 doped with molybdenum (Mo) [6-9] or tungsten (W) [8,10-12] or co-doped with MO and W [13,14] have been observed. To fully understand the performance of these material a fundamental study of the electrical properties of well characterized single crystal was performed. Initial report of transport measurements [15] is available. In this report, enhanced Hall measurements improve these transport measurements for carrier density and mobility to lower temperatures reported in reference 15. Experimental methods Single crystals of BiVO4 were synthesis from ceramic powders. Complete details of crystal synthesis, characterization and sample preparation are given in reference 15. The sample
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geometry was rectangular and resistivity and Hall measurements used the van der Pauw method. The sample was oriented such that the m
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