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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

Dysprosium-doped cadmium oxide as a gateway material for mid-infrared plasmonics

Nature Materials

Sachet, Edward; Shelton, Christopher T.; Harris, Joshua S.; Gaddy, Benjamin E.; Irving, Douglas L.; Curtarolo, Stefano; Donovan, Brian F.; Hopkins, Patrick E.; Sharma, Peter A.; Sharma, Ana L.; Ihlefeld, Jon I.; Franzen, Stefan; Maria, Jon P.

The interest in plasmonic technologies surrounds many emergent optoelectronic applications, such as plasmon lasers, transistors, sensors and information storage. Although plasmonic materials for ultraviolet-visible and near-infrared wavelengths have been found, the mid-infrared range remains a challenge to address: few known systems can achieve subwavelength optical confinement with low loss in this range. With a combination of experiments and ab initio modelling, here we demonstrate an extreme peak of electron mobility in Dy-doped CdO that is achieved through accurate 'defect equilibrium engineering'. In so doing, we create a tunable plasmon host that satisfies the criteria for mid-infrared spectrum plasmonics, and overcomes the losses seen in conventional plasmonic materials. In particular, extrinsic doping pins the CdO Fermi level above the conduction band minimum and it increases the formation energy of native oxygen vacancies, thus reducing their populations by several orders of magnitude. The substitutional lattice strain induced by Dy doping is sufficiently small, allowing mobility values around 500 cm2 V-1 s-1 for carrier densities above 1020 cm-3. Our work shows that CdO:Dy is a model system for intrinsic and extrinsic manipulation of defects affecting electrical, optical and thermal properties, that oxide conductors are ideal candidates for plasmonic devices and that the defect engineering approach for property optimization is generally applicable to other conducting metal oxides.

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TYPE Journal Article YEAR 2015
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Results 26–50 of 67
Results 26–50 of 67