Publication Date

2018-08-03

Availability

Embargoed

Embargo Period

2020-08-03

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Physics (Arts and Sciences)

Date of Defense

2018-05-07

First Committee Member

Joshua L. Cohn

Second Committee Member

Neil F. Johnson

Third Committee Member

Sunxiang Huang

Fourth Committee Member

Francisco M. Raymo

Abstract

Bulk materials with high anisotropic Seebeck coefficient are potentially useful as transverse thermoelectric devices. Molybdenum oxide bronzes are low dimensional materials with high anisotropy in transport properties. Lithium purple bronze Li_0.9 Mo_6 O_17 is a quasi-one dimensional conductor which a large, p-type Seebeck coefficient transverse to its quasi-1-D chains coexists with n-type metallic behavior along the chains. We report on measurements of the transverse Peltier effect on single crystals of lithium purple bronze (LiPB) in the temperature range of 300-500 K which demonstrates one of the largest known transverse Peltier figure of merit for bulk materials. We extend the measurement for a series of single crystals cut with their body axes at varying angles to the q1D chain direction and compare the data to theoretical models that employ known transport coefficients along the mutually perpendicular directions. The result demonstrates that LiPB has one of the largest known values. We also report the transport measurement on single crystals of the closely related quasi-one-dimensional semiconductor Li_0.33 MoO_3, in the temperature range of 150-500 K which shows extreme anisotropy in resistivity and Seebeck coefficients within the a-c plane with transition ~ 360K, accompanied with structural anomaly. This anisotropy appears to be associated with different character of the transport (band-like vs polaron-like) in different crystallographic directions.

Keywords

Low dimensional materials; Thermoelectricity; Molybdenum bronzes; Transport measurement; Transverse Peltier effect; Experimental Solid State Physics

Available for download on Monday, August 03, 2020

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