Tailoring of the electrical and thermal properties using ultra-short period non-symmetric superlattices

Abstract

Thermoelectric modules based on half-Heusler compounds offer a cheap and clean way to create eco-friendly electrical energy from waste heat. Here we study the impact of the period composition on the electrical and thermal properties in non-symmetric superlattices, where the ratio of components varies according to (TiNiSn)(n:)(HfNiSn)(6-n), and 0 <= n <= 6 unit cells. The thermal conductivity (kappa) showed a strong dependence on the material content achieving a minimum value for n = 3, whereas the highest value of the figure of merit ZT was achieved for n = 4. The measured kappa can be well modeled using non-symmetric strain relaxation applied to the model of the series of thermal resistances. (C) 2016 Author(s)

On the thermoelectric properties of Nb-doped SrTiO3 epitaxial thin films

“…For example, r = 0, 1 2 , 1, and 2 can be considered for calculation of Seebeck coefficients when acoustic phonon scattering (or alloy, point-defect scattering), neutral impurities, optical phonon scattering, and the charge impurity scattering, respectively, dominate the conduction process. [54][55][56] Hence, it is likely from our analysis that the scattering mechanism is changing continuously when the thickness of the film reduces gradually. AFM topography images show that the surface of all the films is extremely flat, and there is no sign of any change of the surface morphology as a function of film thickness (see Fig.…”

Subamorphous Thermal Conductivity of Crystalline Half-Heusler Superlattices

“…Where we found a minimum of the k⊥ ~ 1.39 W K -1 m -1 for SL having the same amount of each material. [38] Coming back to the idea of coherent transport, while it is interesting to speak about a possible coherent transport in rough SLs, we cannot proof that the heat transport is influenced by coherent phonons just based on the nearly-linear dependence of k⊥ on the number of periods.…”

“…For this reason, our previous studies were focused on the k reduction through SL structuration. We designed three different experiments to study the impact of the period length [34,37] and the period composition [38] on the electrical and thermal properties of HH SLs. Our findings revealed a room temperature crossover from incoherent to coherent thermal transport in HH SLs.…”

Alloy-Like Behavior of the Thermal Conductivity of Nonsymmetric Superlattices

“…This similitude is resulting from the fact that Eq. ( 5) is a generic description for properties of a two component system, where there is a mutual detrimental influence on the respective property of the other compound [17].…”

“…Figure 3 (a) Thermal conductivity of non-symmetric series of (TiNiSn) d1 :(HfNiSn) d2 SLs as a function of the digital alloy composition, x = d 1 /(d 1 +d 2 ). (b-c) Thermal boundary resistance of (TiNiSn) d1 :( HfNiSn) d2 , cyan dots, as a function of: (b) ratio of material composition with a constant period[17], i.e., d 1 ≠ d 2 ; and (c) period thickness with a constant ratio of the material composition[8], i.e., d 1 = d 2 . As an example, the TBR of (Ti 0.7 W 0.3 N):( Al 0.72 Sc 0.28 N) (orange squares) is also included in (c).…”