Related Experiment Video
Updated: Jun 19, 2026
09:51
Atom Probe Tomography Studies on the CuIn,GaSe2 Grain Boundaries
Published on: April 22, 2013
12.7K
Ag Vacancies as "Killer-Defects" in CaAgSb Thermoelectrics
A K M Ashiquzzaman Shawon1, Ferdaushi Alam Bipasha2, Channyung Lee2
1Department of Chemical Engineering and Material Science, Michigan State University, East Lansing, Michigan 48824, United States.
ACS Applied Energy Materials
|February 28, 2025
Summary
Silver vacancies in CaAgSb Zintl compounds limit thermoelectric performance by causing high p-type carrier concentrations. These "killer defects" prevent n-type doping and hinder optimization of the material's thermoelectric figure of merit (zT).
Area of Science:
- Materials Science
- Solid-State Physics
- Thermoelectrics
Background:
- CaAgSb is a Zintl compound identified as a promising thermoelectric material due to high hole mobility and low lattice thermal conductivity.
- The theoretical thermoelectric figure of merit (zT) of ~1 for CaAgSb requires carrier concentration tuning to ~10^19 cm^-3.
- However, CaAgSb exhibits an intrinsic high p-type carrier concentration (~10^20 cm^-3), limiting zT optimization and preventing n-type doping.
Purpose of the Study:
- To investigate the Fermi-level tunability of CaAgSb using computational and experimental methods.
- To identify the dominant defects responsible for the high intrinsic p-type carrier concentration in CaAgSb.
- To understand the challenges in optimizing CaAgSb for enhanced thermoelectric performance.
Main Methods:
- Density Functional Theory (DFT) defect calculations to determine defect types and their impact on Fermi energy.
- Crystal Orbital Hamilton Population (COHP) analysis to understand bonding characteristics and defect formation energies.
- Experimental phase boundary mapping by synthesizing samples under varying Ca, Ag, and Sb compositions.
Main Results:
- DFT calculations identified acceptor-type defects, specifically Ag-vacancies, as dominant across the chemical potential range, pinning the Fermi energy in the valence band.
- COHP analysis suggests Ag-Sb antibonding orbitals below the Fermi energy contribute to low Ag-vacancy formation energy.
- Experimental synthesis across different phase regions consistently yielded high p-type carrier concentrations (6.0 × 10^19 to 1.8 × 10^20 cm^-3), corroborating DFT predictions.
Conclusions:
- Ag-vacancies are confirmed as the primary 'killer defects' in CaAgSb, responsible for the high intrinsic p-type conductivity.
- These defects limit Fermi-level tuning, posing a significant challenge for optimizing CaAgSb's thermoelectric performance.
- Further research is needed to mitigate the effects of Ag-vacancies for potential n-type doping and improved thermoelectric applications.
More Related Videos
11:45Experimental Methods for Trapping Ions Using Microfabricated Surface Ion Traps
Published on: August 17, 2017
13.6K
06:57Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon
Published on: July 17, 2020
2.1K
Related Concept Videos
01:19Mechanism of heat transfer
Understanding heat transfer mechanisms is essential for understanding how our bodies maintain balance in different environmental conditions. When the environment is thermoneutral, the body is in a state of balance, neither using nor releasing energy to maintain its core temperature. However, when the environment is not thermoneutral, the body employs four heat transfer mechanisms to maintain homeostasis: conduction, convection, evaporation, and radiation. These mechanisms facilitate heat...
01:14Mechanisms of Heat Transfer I
Just as interesting as the effects of heat transfer on a system are the methods by which the heat transfer occur. Whenever there is a temperature difference, heat transfer occurs. It may occur rapidly, such as through a cooking pan, or slowly, such as through the walls of a picnic ice box. So many processes involve heat transfer that it is hard to imagine a situation where no heat transfer occurs. Yet, every heat transfer takes place by only three methods: conduction, convection, and radiation.
01:27Biasing of Metal-Semiconductor Junctions
Biasing metal-semiconductor junctions involves applying a voltage across the junction. Specifically, the metal is connected to a voltage source, while the semiconductor is grounded. This technique is essential for controlling the direction and magnitude of current flow in electronic devices, including diodes, transistors, and photovoltaic cells.
In Schottky junctions, where the semiconductor is n-type, applying a positive voltage to the metal relative to the semiconductor reduces its Fermi...
In Schottky junctions, where the semiconductor is n-type, applying a positive voltage to the metal relative to the semiconductor reduces its Fermi...
01:19Thermal Strain
Thermal strain is a concept that arises when we consider how temperature changes affect structures. Unlike the conventional assumption that structures remain constant under load, real-world scenarios often involve temperature fluctuations that can significantly impact these structures. Consider a homogeneous rod with a uniform cross-section resting freely on a flat horizontal surface. If the rod's temperature increases, the rod elongates. This elongation is proportional to the temperature...
01:26Imperfections in Crystal Structure: Stoichiometric Point Defects
Schottky defects arise when some lattice points in a crystal, such as those in NaCl, remain unoccupied, creating lattice vacancies without disturbing the overall electrical neutrality of the crystal. This defect is common in ionic crystals where the positive and negative ions are similar in size, as seen in sodium chloride and cesium chloride. The presence of Schottky defects enables the crystal to conduct electricity to a small extent through an ionic mechanism. Electric fields cause nearby...
01:29Imperfections in Crystal Structure: Non-Stoichiometric Defects
Non-stoichiometric defects refer to a type of defect in the crystal structure of a compound where the ratio of its constituent elements deviates from the ideal stoichiometric ratio. There are two main types of non-stoichiometric defects: metal excess defects and metal deficiency defects.Metal excess defects occur when there is a slight surplus of metal ions than what is required by the stoichiometric ratio of the compound. For example, heating a sodium chloride crystal in sodium vapor results...