Thermoelectric materials can convert heat into electricity. They are used to generate electricity when other power sources are not available or to increase energy efficiency by recycling waste heat. The Yb 21 Mn 4 Sb 18 phase was previously shown to have good thermoelectric performance due to its large Seebeck coefficient (∼290 μV K −1 ) and low thermal conductivity (0.4 W m −1 K −1 ). These characteristics stem respectively from the unique [Mn 4 Sb 10 ] 22− subunit and the large unit cell/site disorder inherent in this phase. The solid solutions, Yb 21 Mn 4− x Cd x Sb 18 ( x = 0, 0.5, 1.0, 1.5) and Yb 21− y Ca y Mn 4 Sb 18 ( y = 3, 6, 9, 10.5) have been prepared, their structures characterized and thermoelectric properties from room temperature to 800 K measured. A detailed look into the structural disorder for the Cd and Ca solid solutions was performed using synchrotron powder X-ray diffraction and pair distribution function methods and shows that these are highly disordered structures. The substitution of Cd gives rise to more metallic behavior whereas Ca substitution results in high resistivity. As both Cd and Ca are isoelectronic substitutions, the changes in properties are attributed to changes in the electronic structure. Both solid solutions show that the thermal conductivities remain extremely low (∼0.4 W m −1 K −1 ) and that the Seebeck coefficients remain high (>200 μV K −1 ). The temperature dependence of the carrier mobility with increased Ca substitution, changing from approximately T −1 to T −0.5 , suggests that another scattering mechanism is being introduced. As the bonding changes from polar covalent with Yb to ionic for Ca, polar optical phonon scattering becomes the dominant mechanism. Experimental studies of the Cd solid solutions result in a max zT of ∼1 at 800 K and, more importantly for application purposes, a ZT avg ∼ 0.6 from 300 K to 800 K.
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Measured and simulated thermoelectric properties of FeAs 2−x Se x ( x = 0.30–1.0): from marcasite to arsenopyrite structure
FeAs 2−x Se x ( x = 0.30–1.0) samples were synthesized as phase pure powders by conventional solid-state techniques and as single crystals ( x = 0.50) from chemical vapor transport. The composition of the crystals was determined to be Fe 1.025(3) As 1.55(3) Se 0.42(3) , crystallizing in the marcasite structure type, Pnnm space group. FeAs 2−x Se x (0 < x < 1) was found to undergo a marcasite-to-arsenopyrite ( P 2 1 / c space group) structural phase transition at x ∼ 0.65. The structures are similar, with the marcasite structure best described as a solid solution of As/Se, whereas the arsenopyrite has ordered anion sites. Magnetic susceptibility and thermoelectric property measurements from 300–2 K were performed on single crystals, FeAs 1.50 Se 0.50 . Paramagnetic behavior is observed from 300 to 17 K and a Seebeck coefficient of −33 μV K −1 , an electrical resistivity of 4.07 mΩ cm, and a very low κ l of 0.22 W m −1 K −1 at 300 K are observed. In order to determine the impact of the structural transition on the high-temperature thermoelectric properties, polycrystalline FeAs 2−x Se x ( x = 0.30, 0.75, 0.85, 1.0) samples were consolidated into dense pellets for measurements of thermoelectric properties. The x = 0.85 sample shows the best thermoelectric performance. The electronic structure of FeAsSe was calculated with DFT and transport properties were approximately modeled above 500 K.
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- Award ID(s):
- 1709382
- NSF-PAR ID:
- 10249778
- Date Published:
- Journal Name:
- Materials Advances
- Volume:
- 1
- Issue:
- 5
- ISSN:
- 2633-5409
- Page Range / eLocation ID:
- 1390 to 1398
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d0ma00371a
