# Charge carrier effective mass and concentration derived from combination of Seebeck coefficient and ${}^{125}\mathrm{Te}$ NMR measurements in complex tellurides

## Abstract

Thermoelectric materials utilize the Seebeck effect to convert heat to electrical energy. The Seebeck coefficient (thermopower), S, depends on the free (mobile) carrier concentration, n, and effective mass, m*, as S ~ m*/n ^{2/3}. The carrier concentration in tellurides can be derived from ^{125}Te nuclear magnetic resonance (NMR) spin-lattice relaxation measurements. The NMR spin-lattice relaxation rate, 1/T _{1}, depends on both n and m* as 1/T _{1}~(m*) ^{3/2}n (within classical Maxwell-Boltzmann statistics) or as 1/T1~(m*) ^{2}n ^{2/3} (within quantum Fermi-Dirac statistics), which challenges the correct determination of the carrier concentration in some materials by NMR. Here it is shown that the combination of the Seebeck coefficient and ^{125}Te NMR spin-lattice relaxation measurements in complex tellurides provides a unique opportunity to derive the carrier effective mass and then to calculate the carrier concentration. This approach was used to study Ag _{x}Sb _{x}Ge _{50–2x}Te _{50}, well-known GeTe-based high-efficiency tellurium-antimony-germanium-silver thermoelectric materials, where the replacement of Ge by [Ag+Sb] results in significant enhancement of the Seebeck coefficient. Thus, values of both m* and n derived using this combination show that the enhancement of thermopower can be attributed primarily to an increase of the carrier effective mass and partially to a decrease of themore »

- Authors:

- Ames Lab. and Iowa State Univ., Ames, IA (United States)

- Publication Date:

- Research Org.:
- Ames Laboratory (AMES), Ames, IA (United States)

- Sponsoring Org.:
- USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)

- OSTI Identifier:
- 1278781

- Alternate Identifier(s):
- OSTI ID: 1259584

- Report Number(s):
- IS-J-9009

Journal ID: ISSN 2469-9950; PRBMDO

- Grant/Contract Number:
- AC02-07CH11358

- Resource Type:
- Journal Article: Accepted Manuscript

- Journal Name:
- Physical Review B

- Additional Journal Information:
- Journal Volume: 93; Journal Issue: 24; Journal ID: ISSN 2469-9950

- Publisher:
- American Physical Society (APS)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Ag
_{x}Sb_{x}Ge_{50–2x}Te_{50}(TAGS); Seebeck coefficient;^{125}Te NMR spin-lattice relaxation time; charge carrier effective mass and concentration

### Citation Formats

```
Levin, E. M..
```*Charge carrier effective mass and concentration derived from combination of Seebeck coefficient and Te125 NMR measurements in complex tellurides*. United States: N. p., 2016.
Web. doi:10.1103/PhysRevB.93.245202.

```
Levin, E. M..
```*Charge carrier effective mass and concentration derived from combination of Seebeck coefficient and Te125 NMR measurements in complex tellurides*. United States. doi:10.1103/PhysRevB.93.245202.

```
Levin, E. M.. Mon .
"Charge carrier effective mass and concentration derived from combination of Seebeck coefficient and Te125 NMR measurements in complex tellurides". United States. doi:10.1103/PhysRevB.93.245202. https://www.osti.gov/servlets/purl/1278781.
```

```
@article{osti_1278781,
```

title = {Charge carrier effective mass and concentration derived from combination of Seebeck coefficient and Te125 NMR measurements in complex tellurides},

author = {Levin, E. M.},

abstractNote = {Thermoelectric materials utilize the Seebeck effect to convert heat to electrical energy. The Seebeck coefficient (thermopower), S, depends on the free (mobile) carrier concentration, n, and effective mass, m*, as S ~ m*/n2/3. The carrier concentration in tellurides can be derived from 125Te nuclear magnetic resonance (NMR) spin-lattice relaxation measurements. The NMR spin-lattice relaxation rate, 1/T1, depends on both n and m* as 1/T1~(m*)3/2n (within classical Maxwell-Boltzmann statistics) or as 1/T1~(m*)2n2/3 (within quantum Fermi-Dirac statistics), which challenges the correct determination of the carrier concentration in some materials by NMR. Here it is shown that the combination of the Seebeck coefficient and 125Te NMR spin-lattice relaxation measurements in complex tellurides provides a unique opportunity to derive the carrier effective mass and then to calculate the carrier concentration. This approach was used to study AgxSbxGe50–2xTe50, well-known GeTe-based high-efficiency tellurium-antimony-germanium-silver thermoelectric materials, where the replacement of Ge by [Ag+Sb] results in significant enhancement of the Seebeck coefficient. Thus, values of both m* and n derived using this combination show that the enhancement of thermopower can be attributed primarily to an increase of the carrier effective mass and partially to a decrease of the carrier concentration when the [Ag+Sb] content increases.},

doi = {10.1103/PhysRevB.93.245202},

journal = {Physical Review B},

issn = {2469-9950},

number = 24,

volume = 93,

place = {United States},

year = {2016},

month = {6}

}

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