Lattice dynamics and thermoelectric properties of diamondoid materials

The diamondoid compounds are a large family of important semiconductors,which possess various unique transport properties and had been widely investigated in the fields of photoelectricity and nonlinear optics.For a significantly long period of time,diamondoid materials were not given much attention in the field of thermoelectricity.However,this changed when a series of diamondoid compounds showed a thermoelectric figure of merit(ZT)greater than 1.0.This discovery sparked considerable interest in further exploring the thermoelectric properties of diamondoid materials.This review aims to provide a comprehensive view of our current understanding of thermal and electronic transport in diamondoid materials and stimulate their development in thermoelectric applications.We present a collection of recent discoveries concerning the lattice dynamics and electronic structure of diamondoid materials.We review the underlying physics responsible for their unique electrical and phonon transport behaviors.Moreover,we provide insights into the advancements made in the field of thermoelectricity for diamondoid materials and the corresponding strategies employed to optimize their performance.Lastly,we emphasize the challenges that lie ahead and outline potential avenues for future research in the domain of diamondoid thermoelectric materials.

Computational strategies for design and discovery of nanostructured thermoelectrics

The contribution of theoretical calculations and predictions in the development of advanced high-performance thermoelectrics has been increasingly significant and has successfully guided experiments to understand as well as achieve record-breaking results.In this review,recent developments in high-performance nanostructured bulk thermoelectric materials are discussed from the viewpoint of theoretical calculations.An effective emerging strategy for boosting thermoelectric performance involves minimizing electron scattering while maximizing heat-carrying phonon scattering on many length scales.We present several important strategies and key examples that highlight the contributions of first-principles-based calculations in revealing the intricate but tractable relationships for this synergistic optimization of thermoelectric performance.The integrated optimization approach results in a fourfold design strategy for improved materials:(1)a significant reduction of the lattice thermal conductivity through multiscale hierarchical architecturing,(2)a large enhancement of the Seebeck coefficient through intramatrix electronic band convergence engineering,(3)control of the carrier mobility through band alignment between the host and second phases,and(4)design of intrinsically low-thermal-conductivity materials by maximizing vibrational anharmonicity and acoustic-mode Gruneisen parameters.These combined effects serve to enhance the power factor while reducing the lattice thermal conductivity.This review provides an improved understanding of how theory is impacting the current state of this field and helps to guide the future search for high-performance thermoelectric materials.

Accelerated discovery of a large family of quaternary chalcogenides with very low lattice thermal conductivity

The development of efficient thermal energy management devices such as thermoelectrics and barrier coatings often relies on compounds having low lattice thermal conductivity(κl).Here,we present the computational discovery of a large family of 628 thermodynamically stable quaternary chalcogenides,AMM′Q_(3)(A=alkali/alkaline earth/post-transition metals;M/M′=transition metals,lanthanides;Q=chalcogens)using high-throughput density functional theory(DFT)calculations.We validate the presence of lowκl in these materials by calculatingκl of several predicted stable compounds using the Peierls–Boltzmann transport equation.Our analysis reveals that the lowκl originates from the presence of either a strong lattice anharmonicity that enhances the phononscatterings or rattler cations that lead to multiple scattering channels in their crystal structures.Our thermoelectric calculations indicate that some of the predicted semiconductors may possess high energy conversion efficiency with their figure-of-merits exceeding 1 near 600 K.Our predictions suggest experimental research opportunities in the synthesis and characterization of these stable,low κ_(l) compounds.

Achieving Enhanced Thermoelectric Performance in Multiphase Materials

CONSPECTUS:Thermoelectric(TE)devices enable direct solid-state energy conversion from heat to electricity and vice versa,thereby showing great potential in warranting the supply of sustainable energy and mitigating the potentially catastrophic effects of climate change.Therefore,as a clean-energy-generation technology,TE materials have received tremendous research efforts in both industrial and academic communities for applications in the recovery of ubiquitous low-grade waste heat.Achieving high efficiency in TE materials is an ongoing pursuit of the TE research community,considering approximately 90%of all waste heat in the USA comes from medium-temperature(e.g.,from 573 to 873 K)heat sources.Hence,synergistic enhancements in the figures-of-merit(ZT)are still highly desired and remain a key task for improving commercial applications of TE materials.