Anisotropic small-polaron hopping in W:BiVO{sub 4} single crystals

• Published in: Applied physics letters 2015-01, Vol.106 (2)
• Main Authors: Rettie, Alexander J. E., Chemelewski, William D., Zhou, Jianshi, Lindemuth, Jeffrey, McCloy, John S., Materials Science and Engineering Program, Washington State University, Pullman, Washington 99164, Marshall, Luke G., Department of Chemical Engineering, Northeastern University, Boston, Massachusetts 02115, Emin, David, Mullins, C. Buddie, Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712
• Format: Article
• Language: English
• Subjects: ACTIVATION ENERGY; ANISOTROPY; BISMUTH COMPOUNDS; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; DOPED MATERIALS; ELECTRIC CONDUCTIVITY; HALL EFFECT; MONOCLINIC LATTICES; MONOCRYSTALS; N-TYPE CONDUCTORS; POLARONS; SEEBECK EFFECT; TEMPERATURE DEPENDENCE; TUNGSTEN; VANADATES
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4905786

DC electrical conductivity, Seebeck and Hall coefficients are measured between 300 and 450 K on single crystals of monoclinic bismuth vanadate that are doped n-type with 0.3% tungsten donors (W:BiVO{sub 4}). Strongly activated small-polaron hopping is implied by the activation energies of the Arrhenius conductivities (about 300 meV) greatly exceeding the energies characterizing the falls of the Seebeck coefficients' magnitudes with increasing temperature (about 50 meV). Small-polaron hopping is further evidenced by the measured Hall mobility in the ab-plane (10{sup −1 }cm{sup 2 }V{sup −1 }s{sup −1} at 300 K) being larger and much less strongly activated than the deduced drift mobility (about 5 × 10{sup −5 }cm{sup 2 }V{sup −1 }s{sup −1} at 300 K). The conductivity and n-type Seebeck coefficient is found to be anisotropic with the conductivity larger and the Seebeck coefficient's magnitude smaller and less temperature dependent for motion within the ab-plane than that in the c-direction. These anisotropies are addressed by considering highly anisotropic next-nearest-neighbor (≈5 Å) transfers in addition to the somewhat shorter (≈4 Å), nearly isotropic nearest-neighbor transfers.