Effect of interface resistance on thermoelectric properties in (1-x)La0.95_{0.95}Sr0.05_{0.05}Co0.95_{0.95}Mn0.05_{0.05}O3_3/(x)WC composite

In this study, the synergistic effect of the particle size of the dispersed phase and the interface thermal resistance (R$_{int}$) between the phases on the phonon thermal conductivity ($\kappa_{ph}$) of the (1-x)La$_{0.95}$Sr$_{0.05}$Co$_{0.95}$Mn$_{0.05}$O$_3$/(x)WC thermoelectric composite, is demonstrated. Further, the correlation between the R$_{int}$ and the Kapitza radius is discussed using the Bruggeman's asymmetrical model. In particular, the polycrystalline La$_{0.95}$Sr$_{0.05}$Co$_{0.95}$Mn$_{0.05}$O$_3$ sample is synthesized using a standard-solid state route. The presence of WC nanoparticle is confirmed from the electron microscopy images. Electrical conductivity ($\sigma$) increases, and the Seebeck coefficient ($\alpha$) decreases with the increase in conducting WC volume fraction in the composite. The simultaneous increase in $\sigma$ and a decrease in $\kappa_{ph}$ with the WC volume fraction results in an increased figure of merit (zT) for (1-x)La$_{0.95}$Sr$_{0.05}$Co$_{0.95}$Mn$_{0.05}$O$_3$/(x)WC composite. A maximum zT $\sim$ 0.20 is obtained for (1-x)La$_{0.95}$Sr$_{0.05}$Co$_{0.95}$Mn$_{0.05}$O$_3$/(x)WC composite for x=0.010 at 463 K. The results obtained in the present study shows promise to design thermoelectric composites with desired phonon thermal conductivity considering the elastic properties between the phases.Comment: 15 pages, 6 figures, 1 tabl

Effective Thermal Conductivity of SrBi4_4Ti4_4O15_{15}-La0.7_{0.7}Sr0.3_{0.3}MnO3_3 Oxide composite: Role of Particle Size and Interface Thermal Resistance

We present a novel approach to reduce the thermal conductivity ($\kappa$) in thermoelectric composite materials using acoustic impedance mismatch and the Debye model. Also, the correlation between interface thermal resistance (R$_{int}$) and the particle size of the dispersed phase on the k of the composite is discussed. In particular, the $\kappa$ of an oxide composite which consists of a natural superlattice Aurivillius phase (SrBi$_4$Ti$_4$O$_{15}$) as a matrix and perovskite (La$_{0.7}$Sr$_{0.3}$MnO$_3$) as a dispersed phase is investigated. A significant reduction in the $\kappa$ of composite, even lower than the $\kappa$ of the matrix when the particle size of La$_{0.7}$Sr$_{0.3}$MnO$_3$ is smaller than the Kapitza radius (a$_K$) is observed, depicting that R$_{int}$ dominates for particle size lower than a$_K$ due to increased surface to volume ratio. The obtained results have the potential to provide new directions for engineering composite thermoelectric systems with desired thermal conductivity and promising in the field of energy harvesting.Comment: 21 pages, 8 Figures, 5 Table

Discovery of the high thermoelectric performance in low-cost Cu8SiSxSe6-x argyrodites

Cu-based argyrodites have gained much attention as a new class of thermoelectric materials for energy harvesting. However, the phase transition occurring in these materials and low energy conversion performance limited their broad application in thermoelectric converters. In this work, we disclose a newly discovered highly efficient Cu8SiSxSe6-x argyrodite with stabilized high-symmetry cubic phase at above 282 K opening the practical potential of this material for the mid-temperature region applications. The temperature range broadening of the high-symmetry phase existence was possible due to the successful substitution of Se with S in Cu8SiSxSe6-x, which enhances the configurational entropy. The developed argyrodites show excellent thermoelectric performance thanks to the increased density of states effective mass and ultralow lattice thermal conductivity. Further tuning of the carrier concentration through the Cu-deviation improves the thermoelectric performance significantly. The dimensionless thermoelectric figure of merit ZT and estimated energy conversion efficiency {\eta} for Cu7.95SiS3Se3 achieve outstanding values of the 1.45 and 13 %, respectively, offering this argyrodite as a low-cost and Te-free alternative for the thermoelectric energy conversion applications.Comment: 25 pages, 8 figure

Origin of low thermal conductivity in In4Se3

In4Se3 is an attractive n-type thermoelectric material for mid-range waste heat recovery, owing to its low thermal conductivity (~ 0.9 W∙m- 1 K- 1 at 300 K). Here, we explore the relationship between the elastic properties, thermal conductivity and structure of In4Se3. The experimentally-determined average sound velocity (2010 m s-1), Young’s modulus (47 GPa), and Debye temperature (198 K) of In4Se3 are rather low, indicating considerable lattice softening. This behavior, which is consistent with low thermal conductivity, can be related to the complex bonding found in this material, in which strong covalent In-In and In-Se bonds coexist with weaker electrostatic interactions. Phonon dispersion calculations show that Einstein-like modes occur at ~ 30 cm-1. These Einstein-like modes can be ascribed to weakly bonded In+ cations located between strongly-bonded [(In3)5+(Se2-)3]- layers. The Grüneisen parameter for the soft-bonded In+ at the frequencies of the Einstein-like modes is large, indicating a high degree of bond anharmonicity and hence increased phonon scattering. The calculated thermal conductivity and elastic properties are in good agreement with experimental results