Project Details
Projekt
Ab initio based multiscale simulations of domain structures in thermoelektric materials
Applicant
Privatdozent Dr. Thomas Gruhn
Subject Area
Theoretical Condensed Matter Physics
Term
from 2012 to 2018
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 220269302
The reduction of the thermal lattice conductivity is an important objective in the development of new thermoelectric materials. Low lattice conductivities are found in materials with suitable nanostructures. In some compounds such a structure formation occurs spontaneously due to a phase segregation of components. In this project, we use ab-initio based multiscale simulations to study the domain formation and the resulting thermal lattice conductivity of thermoelectric materials that show partial demixing. The focus of the investigations will be on the thermoelectric half-Heusler material CoTi1-xMnxSb, which shows a partial segregation on one of the three sublattices. The simulations provide information about the segregation type and the shape of the domains as a function of the temperature and the stoichiometry of the system. Furthermore, we investigate the dynamics of the domain formation and the thermal lattice conductivity of differently structured materials. The material properties are determined with the help of Monte Carlo simulations and phase field methods. The simulations are based on a cluster expansion of the configurational energy that we derive from quantum mechanical density functional calculations. The Monte Carlo simulations are used to analyze the coexistence region of the alloy. This allows predicting whether a given compound demixes by cluster growth or by spinodal decomposition. Monte Carlo simulations of the domain boundary and its regularity help to determine a material with an optimum phonon damping. The phase field method is used to determine the three-dimensional domain structure on a larger length scale, which is very difficult to investigate, experimentally. The thermal lattice conductivity is calculated for nano and micro-structured materials, showing which domain structures lead to especially low heat conduction. The phase field method is also used to study the dynamics of segregation, which gives information on the persistence of the domain structures. The aim of all the numerical studies is to determine the structural and thermal properties of the compounds as a function of the composition and the production parameters in order to provide guide lines for the development of optimized thermoelectric materials.
DFG Programme
Priority Programmes
