Journal
PHYSICAL REVIEW B
Volume 85, Issue 14, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.85.144120
Keywords
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Funding
- US Department of Energy, Office of Energy Efficiency and Renewable Energy
- Center on Revolutionary Materials for Solid State Energy Conversion, an Energy Frontier Research Center
- US Department of Energy, Office of Basic Energy Sciences [DE-SC0001054]
- US Department of Energy [DE-AC05-00OR22725]
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Materials with the half-Heusler structure possess interesting electrical and magnetic properties, including potential for thermoelectric applications. MgAgSb is compositionally and structurally related to many half-Heusler materials but has not been extensively studied. This work presents the high-temperature x-ray diffraction analysis of MgAgSb between 27 and 420 degrees C, complemented with thermoelectric property measurements. MgAgSb is found to exist in three different crystal structures in this temperature region, taking the half-Heusler structure at high temperatures, a Cu2Sb-related structure at intermediate temperatures, and a previously unreported tetragonal structure at room temperature. All three structures are related by a distorted Mg-Sb rocksalt-type sublattice, differing primarily in the Ag location among the available tetrahedral sites. Transition temperatures between the three phases correlate well with discontinuities in the Seebeck coefficient and electrical conductivity; the best performance occurs with the novel room temperature phase. For application of MgAgSb as a thermoelectric material, it may be desirable to develop methods to stabilize the room temperature phase at higher temperatures.
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