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Low effective mass and carrier concentration optimization for high performance p-type Mg2(1-x)Li2xSi0.3Sn0.7 solid
Qiang Zhang1, Long Cheng, Wei Liu
1State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China. tangxf@whut.edu.cn.
Physical Chemistry Chemical Physics : PCCP
|September 3, 2014
Summary
Lithium doping significantly enhances p-type Mg2Si1-xSnx thermoelectric materials by increasing hole carriers and power factor. This research achieves a 30% improvement in the figure of merit (ZT) for these promising materials.
Area of Science:
- Materials Science
- Solid-state Physics
- Thermoelectrics
Background:
- Mg2Si1-xSnx solid solutions are promising for thermoelectric power generation (500-800 K).
- While n-type materials show high performance (ZT ~ 1.4), p-type counterparts lag significantly.
- Effective p-type doping is crucial for advancing these thermoelectric materials.
Purpose of the Study:
- To enhance and control hole carrier concentration in p-type Mg2Si1-xSnx using Lithium (Li) doping.
- To investigate the impact of Li doping on thermoelectric properties, particularly the power factor and figure of merit (ZT).
- To explore strategies for optimizing p-type thermoelectric performance by manipulating electronic band structure.
Main Methods:
- Li doping was introduced on Mg sites in Mg2Si1-xSnx solid solutions.
- Electrical conductivity, Seebeck coefficient, and power factor were measured.
- Theoretical calculations explored the electronic band structure and density of states (DOS).
- Low-temperature specific heat capacity studies determined the DOS effective mass.
Main Results:
- Li was identified as a highly effective p-type dopant, surpassing Na and K.
- Increased Li content led to higher electrical conductivity due to enhanced hole density.
- A robust power factor was maintained despite a decrease in Seebeck coefficient, attributed to high hole mobility.
- Theoretical and experimental data indicated a low DOS effective mass in Li-doped samples, promoting hole mobility.
- A figure of merit (ZT) of ~0.5 at 750 K was achieved for Mg2Si0.93Sn0.07 doped with Li, a 30% improvement.
Conclusions:
- Li doping is a superior strategy for enhancing p-type Mg2Si1-xSnx thermoelectric materials.
- Designing materials with a low DOS near the Fermi level is key to optimizing power factor and ZT.
- This work provides a significant advancement for p-type thermoelectric materials in mid-temperature applications.
