If you have read anything about our 8400 Series HMS, you know that when used with its AC field Hall option, it’s capable of measuring low-mobility materials. These are the types of materials with electron mobilities that can’t often be measured using traditional DC field Hall methods. One such material is bismuth vanadate (BiVO4) — a promising metal oxide material that will, hopefully, be a key catalyst in the production of hydrogen fuel from solar energy using photoelectrical (PEC) water splitting.
If the subject of measuring BiVO4 interests you, then be sure to read this recently published MRS Online article, “Electronic Transport Characterization of BiVO4 Using AC Field Hall Technique.” The paper, co-authored by Lake Shore’s Dr. Jeffrey Lindemuth and University of Texas researchers Alexander J. E. Rettie, Luke G. Marshall, Jianshi Zhou, and C. Buddie Mullins, examines how AC field Hall effect measurements can be beneficial in understanding the intrinsic electrical and photoelectrochemical properties of BiVO4 materials. Since early 2013, Lindemuth and the University of Texas team have been studying how to best determine carrier concentration and electron mobility values for synthesized BiVO4 crystals when measuring resistivity and the Hall effect as a function of temperature. Because metal oxides such as BiVO4 become more electrically resistive at different temperatures, knowing these changing values can be a very important part of designing new PEC solar cells.
In a 2013 Journal of Chemical Society paper, Lindemuth and the team were able to measure the mobility of BiVO4 material from room temperature to 250 K. But, as detailed in the recent MRS Online paper, they have now been able to extend the measurements to 175 K. This was done by improving the filtering used in the AC Hall measurement. They found that the mobility decreased from 0.1 cm2/V s at 250 K to 0.03 cm2/V s at 175 K. The temperature dependency of the carrier density and resistance was consistent with variable range hopping theory above 250 K and small polaron hopping below 250 K.