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research: experimental validation

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Materials synthesis and characterization

experiments: Cedomir Petrovic, Qianheng Du
material growth: Cedomir Petrovic, Qianheng Du
theory: Gabriel Kotliar

The materials synthesis and characterization laboratories supported by Comscope synthesize materials and perform characterization of their basic structural and physical properties. Its methods of crystal growth range from molten metallic fluxes to chemical vapor transport. The characterization of physical properties includes thermal, thermodynamic, magnetic, and transport measurements whereas structural properties are investigated by powder and single crystal X-ray diffraction. 

For Comscope we in particular synthesize and characterize materials with large thermoelectric power such as FeSb2 and related compounds. We have discovered that the thermoelectric power in FeSb2 is very dependent on the impurity content. Crystals with low thermoelectric power always show compensated carrier concentrations n and identical mobility μ at 300 K whereas crystals with high thermoelectric power show rather disparate values of n and μ. The sign of the thermopower as a function of temperature in all crystals exactly tracks the sign of the low mobility band.  The amplification in high thermopower crystals coincides with a high phonon mean free path, therefore it is plausible to conclude that the so-called phonon drag mechanism might be active in such crystals (but see our optics work).

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Sample dependence of FeSb2 crystals with different purity.

Besides FeSb2, we have synthesized FeP2, FeSe2, FeTe2, CrSb2, NiSb2, CoSb2, RuSb2, and OsTe2. It is found that the crystal structure and  the conductivity can be tuned by chemical substitutions. Detailed investigation of their properties, in particular correlated electron thermoelectricity, is under way.

Related Publications

Impurity in-gap states in colossal thermopower of iron diantimonide.
Qianheng Du, G. Kotliar, and C. Petrovic,
In preparation (2018)

Low temperature thermoelectricity in CoSbS.
Qianheng Du, Yu Liu, G. Kotliar, and C. Petrovic,
Submitted (2017)

Polaronic transport and thermoelectricity in Fe1-xCoxSb2S4 (x=0, 0.1 and 0.2)
Yu Liu, Chang-Jong Kang, Eli Stavitski, Qianheng Du, Klaus Attenkofer, G. Kotliar, and C. Petrovic, Phys. Rev. B 97, 155202 (2018)

Superconducting order from Disorder in 2H-TaSe2-xSx.
Lijun Li, Xiaoyu Deng, Zhen Wang, Yu Liu, Milinda Abeykoon, Eric Dooryhee, Aleksandra Tomic, Yanan Huang, John B. Warren, Emil S. Bozin, Simon J. L. Billinge, Yuping Sun, Yimei Zhu, Gabriel Kotliar, and Cedomir Petrovic,
Nature Partner Journal Quantum Materials 2, 11 (2017)