The narrow band gap semiconductor iron antimonide, FeSb2, has been grown as bulk single crystals, and investigated for its electronic and magnetic properties at low temperatures. The electronic behavior of FeSb2 is associated with strong electron correlations, similar to the characteristic behavior observed in FeSi, another strongly correlated d-electron correlated semiconductor. Recent studies found an enhancement of the Seebeck coefficient and thermopower, two key parameters in thermoelectric performance, at temperatures below 77K, making FeSb2 potentially useful in cryogenic Peltier-cooling applications below liquid nitrogen temperatures. Crystals with sizes of 1.5-5.0 mm are grown using three different synthesis approaches: chemical vapor-phase transport (CVT), using either chlorine (Cl2(g)) or iodine (I2(g)) as transporting agents, and molten flux growth using excess antimony (Sb). Single crystal and powder x-ray diffraction experiments on select samples provided for structural phase identification and confirmed the absence of secondary impurity phases. FeSb2 crystallizes in the FeS2-marcasite structure type, featuring FeSb6 edge-sharing octahedra forming chains along the c-axis and corner-sharing in the a-b plane. The crystal surfaces were characterized using SEM-EDS and AFM measurements, revealing the characteristic morphological features resulting from CVT growth, as well as helping to identify surface contamination. Magnetic susceptibility measurements show weak temperature induced paramagnetism above 50K, with the diamagnetic-to-paramagnetic crossover above 100K. Temperature-dependent electronic transport properties, ρ(T), showed semiconducting behavior and the formation of a resistivity plateau between 10K-40K, corresponding to a secondary transport gap, εg, of about 3.9-7.2meV, similar in magnitude and in accordance to previous studies on FeSb2. Hybridization between iron (Fe) 3d and antimony (Sb) 5p and 5s valence states appears to be responsible for complex electronic behavior at low temperatures, with the formation of a small secondary gap. Earlier studies have shown a significant enhancement of the Seebeck coefficient (thermopower) at the onset of this gap (10K-12K). Thermopower measurements in our sample also show peak values around this temperature, but the maximum values are several orders of magnitude lower than previous reports, while magnetic and electronic properties are in good agreement. / A Thesis submitted to the Interdisciplinary Program in Materials Science in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester, 2012. / May 22, 2012. / Correlated Systems, FeSb2, FeSi, Peltier cooling, Seebeck Coefficient, Thermoelectrics / Includes bibliographical references. / Theo Siegrist, Professor Directing Thesis; Eric Hellstrom, Committee Member; James Brooks, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_183167 |
| Contributors | Lombardo, Rafael Vasquez (authoraut), Siegrist, Theo (professor directing thesis), Hellstrom, Eric (committee member), Brooks, James (committee member), Program in Materials Science (degree granting department), Florida State University (degree granting institution) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource, computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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