TELIOTES project

In late January 2018 I was awarded with a Marie Skłodowska-Curie individual fellowship to study the thermoelectric properties of superlattices made of trichalcogenides and organic nanostructures. This study is part of a project called Thermal and ELectronic Transport in Inorganic-Organic ThermoElectric Superlattices (TELIOTES) at the Institut de Ciències de Materials de Barcelona (ICMAB) (Institute of Materials Science of Barcelona).

Motivation

The global older population will double its current size by 2050, reaching 2.1 billion. As a result, further medical attention for this increasing population will require a new generation of more reliable and energy-efficient medical devices. Devices such as therapeutic wraps and blankets can benefit from materials that can generate cold from electricity without moving parts, minimising the discomfort on the patient. These materials are called thermoelectrics because they convert electricity into cold or heat, or vice versa. However, their use as therapeutic tools is limited because they are currently made with brittle and often toxic compounds. Luckily, this limitation can be overcome by replacing these compounds by flexible materials such as polymers.

Therefore, the goal of this action is to investigate how efficient is the generation of cold with these new polymer-based hybrid materials under different conditions. As these hybrid materials will be bent or even twisted during their use, this action goes beyond the typical studies, where their efficiency is studied in ideal conditions with no deformation, to answer the following question: how does this efficiency vary when the material is strained?

This action is not only aimed at policymakers and medical doctors to show them the benefits of fundamental research on thermoelectric materials, but also at the scientific community and patent engineers to provide cutting-edge results to guide them in building the next generation of medical devices for the senior members of our communities.

Methodology

We apply unidirectional strains of up to ± 10 % in the x and y directions of TiS₃ monolayers with a vacuum gap of 1.4 nm.

We then follow these steps:

• 1. We use the DFT code VASP to relax the positions and cell vectors. Note that we when apply strain in the x-direction, we let the cell relax in the y-direction and viceversa.

  2. Once the geometry is relaxed, the electronic structure is calculated using the HSE06 as this functional predicts a band gap close to the experimental value.

  3. We then compute with the BoltzTrap code the following electronic properties:

     • Seebeck coefficient S,

     • electrical conductivity sigma, and

     • electronic contribution to thermal conductivity k_el.

  4. We finally calculate with the almaBTE code the thermoelectric properties:

     • phonon contribution to thermal conductivity k_ph, and other properties such as

     • phonon group velocities, scattering times, and heat capacity.