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Title: Three-dimensional multimodal imaging and analysis of biphasic microstructure in a Ti–Ni–Sn thermoelectric material

Abstract

The three-dimensional microstructure of levitation melted TiNi{sub 1.20}Sn has been characterized using the TriBeam system, a scanning electron microscope equipped with a femtosecond laser for rapid serial sectioning, to map the character of interfaces. By incorporating both chemical data (energy dispersive x-ray spectroscopy) and crystallographic data (electron backscatter diffraction), the grain structure and phase morphology were analyzed in a 155 μm × 178 μm × 210 μm volume and were seen to be decoupled. The predominant phases present in the material, half-Heusler TiNiSn, and full-Heusler TiNi{sub 2}Sn have a percolated structure. The distribution of coherent interfaces and high-angle interfaces has been measured quantitatively.

Authors:
;  [1];  [2]; ;  [1];  [1];  [2];  [2]
  1. Materials Department, University of California, Santa Barbara, California 93106 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
22499242
Resource Type:
Journal Article
Resource Relation:
Journal Name: APL Materials; Journal Volume: 3; Journal Issue: 9; Other Information: (c) 2015 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CRYSTALLOGRAPHY; DIFFRACTION; MICROSTRUCTURE; SCANNING ELECTRON MICROSCOPY; THERMOELECTRIC MATERIALS; THREE-DIMENSIONAL LATTICES; X-RAY SPECTROSCOPY

Citation Formats

Douglas, Jason E., E-mail: jedouglas@mrl.ucsb.edu, Pollock, Tresa M., Materials Research Laboratory, University of California, Santa Barbara, California 93106, Echlin, McLean P., Lenthe, William C., Seshadri, Ram, Materials Research Laboratory, University of California, Santa Barbara, California 93106, and Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106. Three-dimensional multimodal imaging and analysis of biphasic microstructure in a Ti–Ni–Sn thermoelectric material. United States: N. p., 2015. Web. doi:10.1063/1.4931764.
Douglas, Jason E., E-mail: jedouglas@mrl.ucsb.edu, Pollock, Tresa M., Materials Research Laboratory, University of California, Santa Barbara, California 93106, Echlin, McLean P., Lenthe, William C., Seshadri, Ram, Materials Research Laboratory, University of California, Santa Barbara, California 93106, & Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106. Three-dimensional multimodal imaging and analysis of biphasic microstructure in a Ti–Ni–Sn thermoelectric material. United States. doi:10.1063/1.4931764.
Douglas, Jason E., E-mail: jedouglas@mrl.ucsb.edu, Pollock, Tresa M., Materials Research Laboratory, University of California, Santa Barbara, California 93106, Echlin, McLean P., Lenthe, William C., Seshadri, Ram, Materials Research Laboratory, University of California, Santa Barbara, California 93106, and Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106. Tue . "Three-dimensional multimodal imaging and analysis of biphasic microstructure in a Ti–Ni–Sn thermoelectric material". United States. doi:10.1063/1.4931764.
@article{osti_22499242,
title = {Three-dimensional multimodal imaging and analysis of biphasic microstructure in a Ti–Ni–Sn thermoelectric material},
author = {Douglas, Jason E., E-mail: jedouglas@mrl.ucsb.edu and Pollock, Tresa M. and Materials Research Laboratory, University of California, Santa Barbara, California 93106 and Echlin, McLean P. and Lenthe, William C. and Seshadri, Ram and Materials Research Laboratory, University of California, Santa Barbara, California 93106 and Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106},
abstractNote = {The three-dimensional microstructure of levitation melted TiNi{sub 1.20}Sn has been characterized using the TriBeam system, a scanning electron microscope equipped with a femtosecond laser for rapid serial sectioning, to map the character of interfaces. By incorporating both chemical data (energy dispersive x-ray spectroscopy) and crystallographic data (electron backscatter diffraction), the grain structure and phase morphology were analyzed in a 155 μm × 178 μm × 210 μm volume and were seen to be decoupled. The predominant phases present in the material, half-Heusler TiNiSn, and full-Heusler TiNi{sub 2}Sn have a percolated structure. The distribution of coherent interfaces and high-angle interfaces has been measured quantitatively.},
doi = {10.1063/1.4931764},
journal = {APL Materials},
number = 9,
volume = 3,
place = {United States},
year = {Tue Sep 01 00:00:00 EDT 2015},
month = {Tue Sep 01 00:00:00 EDT 2015}
}
  • Thermoelectric properties and phase evolution have been studied in biphasic Ti–Ni–Sn materials containing full-Heusler TiNi 2Sn embedded within half-Heusler thermoelectric TiNiSn. Materials, prepared by levitation induction melting followed by annealing, were of the nominal starting composition of TiNi 1+x Sn, with x between 0.00 and 0.25. Phases and microstructure were determined using synchrotron X-ray diffraction and optical and electron microscopy. The full-Heusler phase is observed to be semi-coherent with the half-Heusler majority phase. Differential thermal analysis was performed to determine melting temperatures of the end-member compounds. The thermal conductivity is reduced with the introduction of a dispersed, full-Heusler phase withinmore » the half-Heusler material. This leads to an increased thermoelectric figure of merit, ZT, from 0.35 for the stoichiometric compound to 0.44 for TiNi 1.15Sn. Beyond x = 0.15 ZT decreases due to a rise in thermal conductivity. Density functional theory calculations using hybrid functionals were performed to determine band alignments between the half- and full-Heusler compounds, as well as comparative energies of formation. The hybrid functional band structure of TiNiSn is presented as well.« less
  • Thermoelectric properties and phase evolution have been studied in biphasic Ti–Ni–Sn materials containing full-Heusler TiNi{sub 2}Sn embedded within half-Heusler thermoelectric TiNiSn. Materials, prepared by levitation induction melting followed by annealing, were of the nominal starting composition of TiNi{sub 1+x}Sn, with x between 0.00 and 0.25. Phases and microstructure were determined using synchrotron X-ray diffraction and optical and electron microscopy. The full-Heusler phase is observed to be semi-coherent with the half-Heusler majority phase. Differential thermal analysis was performed to determine melting temperatures of the end-member compounds. The thermal conductivity is reduced with the introduction of a dispersed, full-Heusler phase within themore » half-Heusler material. This leads to an increased thermoelectric figure of merit, ZT, from 0.35 for the stoichiometric compound to 0.44 for TiNi{sub 1.15}Sn. Beyond x = 0.15 ZT decreases due to a rise in thermal conductivity. Density functional theory calculations using hybrid functionals were performed to determine band alignments between the half- and full-Heusler compounds, as well as comparative energies of formation. The hybrid functional band structure of TiNiSn is presented as well.« less
  • We report a half-Heusler (HH) derivative Ti{sub 9}Ni{sub 7}Sn{sub 8} with VEC = 17.25 to investigate the structural changes for the optimization of high thermoelectric performance. The structural analysis reveals that the resulting material is a nanocomposite of HH and full-Heusler with traces of Ti{sub 6}Sn{sub 5} type-phase. Interestingly, present nanocomposite exhibits a significant decrease in thermal conductivity due to phonon scattering and improvement in the power factor due to combined effect of nanoinclusion-induced electron injection and electron scattering at interfaces, leading to a boost in the ZT value to 0.32 at 773 K, which is 60% higher than its bulk counterpart HHmore » TiNiSn.« less