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Instrument for stable high temperature Seebeck coefficient and resistivity measurements under controlled oxygen partial pressure

Journal of Materials Science

Brown-Shaklee, Harlan J.; Sharma, Peter A.; Ihlefeld, Jon I.

The transport properties of ceramic materials strongly depend on oxygen activity, which is tuned by changing the partial oxygen pressure (pO2) prior to and during measurement. Within, we describe an instrument for highly stable measurements of Seebeck coefficient and electrical resistivity at temperatures up to 1300 K with controlled oxygen partial pressure. An all platinum construction is used to avoid potential materials instabilities that can cause measurement drift. Two independent heaters are employed to establish a small temperature gradient for Seebeck measurements, while keeping the average temperature constant and avoiding errors associated with pO2-induced drifts in thermocouple readings. Oxygen equilibrium is monitored using both an O2 sensor and the transient behavior of the resistance as a proxy. A pO2 range of 10−25–100 atm can be established with appropriate gas mixtures. Seebeck measurements were calibrated against a high purity platinum wire, Pt/Pt–Rh thermocouple wire, and a Bi2Te3 Seebeck coefficient Standard Reference Material. To demonstrate the utility of this instrument for oxide materials we present measurements as a function of pO2 on a 1 % Nb-doped SrTiO3 single crystal, and show systematic changes in properties consistent with oxygen vacancy defect chemistry. An approximately 11 % increase in power factor over a pO2 range of 10−19–10−8 atm at 973 K for the donor-doped single crystals is observed.

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TYPE Journal Article YEAR 2015
ScopusOSTIDOI

Glass-like thermal conductivity of (010)-textured lanthanum-doped strontium niobate synthesized with wet chemical deposition

Journal of the American Ceramic Society

Foley, Brian M.; Brown-Shaklee, Harlan J.; Campion, Michael J.; Medlin, Douglas L.; Clem, Paul G.; Ihlefeld, Jon I.; Hopkins, Patrick E.

We have measured the cross-plane thermal conductivity (κ) of (010)-textured, undoped, and lanthanum-doped strontium niobate (Sr2-xLaxNb2O7-δ) thin films via time-domain thermoreflectance. The thin films were deposited on (001)-oriented SrTiO3 substrates via the highly-scalable technique of chemical solution deposition. We find that both film thickness and lanthanum doping have little effect on κ, suggesting that there is a more dominant phonon scattering mechanism present in the system; namely the weak interlayer-bonding along the b-axis in the Sr2Nb2O7 parent structure. Furthermore, we compare our experimental results with two variations of the minimum-limit model for κ and discuss the nature of transport in material systems with weakly-bonded layers. The low cross-plane κ of these scalably-fabricated films is comparable to that of similarly layered niobate structures grown epitaxially.

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TYPE Journal Article YEAR 2014
ScopusOSTIDOI

Thermal boundary conductance accumulation and spectral phonon transmission across interfaces: experimental measurements across metal/native oxide/Si and metal/sapphire interfaces

Nature Communications

Ihlefeld, Jon I.; Brown-Shaklee, Harlan J.; Cheaito, Ramez C.; Gaskins, John T.; Caplan, Matthew E.; Donovan, Brian F.; Foley, Brian M.; Giri, Ashutosh G.; Duda, John C.; Szwejkowski, Chester J.; Constantin, Costel C.; Hopkins, Patrick E.

Abstract not provided.

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TYPE Journal Article YEAR 2014
OSTI
Results 51–75 of 103
Results 51–75 of 103