arXiv subjects

Wenling Ren

Publications and source records attributed to Wenling Ren.

4 recordsLinked to original sources

arXiv2026

Anion Engineering Enables Concurrent Optimization of Phonon and Carrier Transport in AMg$_2$X$_2$ Zintl Thermoelectrics

The simultaneous suppression of lattice heat transport and enhancement of carrier transport is central to the development of high-performance thermoelectric materials. Here, we investigate the microscopic mechanisms governing phonon and carrier transport in CaAl$_2$Si$_2$-type AMg$_2$X$_2$ (A = Ca, Sr, Ba; X = P, As, Sb, Bi) Zintl compounds using first-principles calculations, machine-learning interatomic potentials, and Boltzmann transport theory. As X changes from P to Bi, the widening phonon band gap restricts three-phonon scattering channels and increases the relative importance of four-phonon processes. In CaMg$_2$Bi$_2$ and BaMg$_2$Bi$_2$, four-phonon scattering dominates the relaxation of low-frequency heat-carrying modes at 900 K. The Bi-based series also exhibits an anomalous increase in lattice thermal conductivity from Ca to Ba despite the increasing cation mass. Mode-resolved analysis links the lower thermal conductivity of CaMg$_2$Bi$_2$ to reduced low-frequency group velocities and stronger anharmonic scattering, with Ca-related mid-frequency vibrations providing additional four-phonon scattering channels. Including both particle-like and coherent contributions, its lattice thermal conductivity reaches 0.23 W$\cdot$m$^{-1}$K$^{-1}$ at 900 K. Meanwhile, the increasing covalent character of the vertical Mg-X bonds is accompanied by enhanced band-edge dispersion and reduced carrier effective masses. These electronic changes, together with conduction-band convergence, favor n-type transport and yield a predicted peak $ZT$ of 3.68 at 900 K in CaMg$_2$Bi$_2$. These results elucidate the interplay of phonon spectral structure and higher-order anharmonicity in thermal transport, alongside the distinct electronic response to anion substitution.

cond-mat.mtrl-sci↗

arXiv2026

Anharmonicity Driven by Vacancy Ordering Unlocks High-performance Thermoelectric Conversion in Defective Chalcopyrites II-III$_2$-VI$_4$

Defective chalcopyrites have recently emerged as promising thermoelectric materials because their ordered intrinsic vacancies can profoundly reshape both lattice dynamics and electronic structure. Here, we present a comprehensive theoretical investigation of the lattice thermal and carrier transport properties of II-III$_2$-VI$_4$ defective chalcopyrites by combining first-principles calculations with machine-learning interatomic potentials. We show that vacancy ordering enhances lattice distortion, leading to strong anharmonicity and metavalent bonding. The interplay of soft low-frequency phonons, strongly negative Grüneisen parameters, and a substantially enlarged four-phonon scattering phase space results in four-phonon-scattering-dominated heat transport, yielding ultralow lattice thermal conductivity. Meanwhile, systematic anion substitution at the VI-site provides an effective route to tune the electronic structure: reduced anion electronegativity weakens metal-anion hybridization, shifts anion $p$ states upward, narrows the band gap, and thereby improves electrical transport. Benefiting from this synergy between vacancy-induced phonon suppression and anion-regulated electronic optimization, CdGa$_2$Te$_4$ exhibits an ultralow lattice thermal conductivity of 0.19 W$\cdot$m$^{-1}$K$^{-1}$ and a high room-temperature $ZT$ of 0.957. This work not only predicts defective chalcopyrites as a promising platform for high-performance thermoelectrics but also provides a practical design strategy by integrating vacancy ordering, higher-order phonon scattering, and anion-dependent band engineering.

cond-mat.mtrl-sci↗

arXiv2024

Hierarchical Characterization of Thermoelectric Performance in Copper-Based Chalcogenide CsCu$_3$S$_2$: Unveiling the role of Anharmonic Lattice Dynamics

We explicitly consider both phonon energy shifts and broadening arising from both cubic and quartic anharmonicities, as well as diagonal/non-diagonal terms of heat flux operators in thermal conductivity. Our findings show that the strong anharmonicity of CsCu$_3$S$_2$ primarily arises from the presence of $p$-$d$ anti-bonding hybridization between Cu and S atoms, coupled with the random oscillations of Cs atoms. Notably, the competition between phonon hardening described by the loop diagram and softening induced by the bubble diagram significantly influences particle-like propagation, predominantly reflected in group velocity and energy-conservation rule. Additionally, the electrical transport properties are determined by employing the precise momentum relaxation-time approximation (MRTA). At high temperatures, the thermoelectric performance of $p$-type CsCu$_3$S$_2$ reaches its optimum theoretical value of 0.94 along the in-plane direction based on advanced phonon renormalization theory. In striking contrast, the harmonic approximation theory significantly overestimates the thermoelectric efficiency at the same temperatures, rendering it an impractical expectation. Conversely, the first-order renormalization approach leads to a serious underestimation of the thermoelectric properties due to the over-correction of phonon energy. Our study not only reveals the pivotal role of anharmonic lattice dynamics in accurately assessing thermoelectric properties but also underscores the potential thermoelectric applications for novel copper-based chalcogenides.

cond-mat.mtrl-sci↗

arXiv2024

Ultra-low glassy thermal conductivity and controllable, promising thermoelectric properties in crystalline o-CsCu5S3

We thoroughly investigate the microscopic mechanisms of the thermal transport in orthorhombic \textit{o}-CsCu$_5$S$_3$ by integrating the first-principles-based self-consistent phonon calculations (SCP) with the linearized Wigner transport equation (LWTE). Our methodology takes into account contributions to phonon energy shifts and phonon scattering rates from both three- and four-phonon processes. Additionally, it incorporates the off-diagonal terms of heat flux operators to calculate the total thermal conductivity. The predicted $κ_\mathrm{L}$ with an extremely weak temperature dependence following $\sim T^{-0.33}$, in good agreement with experimental values along with the parallel to the Bridgman growth direction. Such nonstandard temperature dependence of $κ_\mathrm{L}$ can be traced back to the dual particlelike-wavelike behavior exhibited by thermal phonons. Specifically, the coexistence of the stochastic oscillation of Cs atoms and metavalent bonding among interlayer Cu-S atoms limits the particle-like phonon propagation and enhances the wave-like tunneling of phonons. Simultaneously, the electrical transport properties are determined by employing a precise momentum relaxation-time approximation (MRTA) within the framework of the linearized Boltzmann transport equation (LBTE). By properly adjusting the carrier concentration, excellent thermoelectric performance is achieved, with a maximum thermoelectric conversion efficiency of 18.4$\%$ observed at 800 K in \textit{p}-type \textit{o}-CsCu$_5$S$_3$.} Our work not only elucidates the anomalous thermal transport behavior in the copper-based chalcogenide \textit{o}-CsCu$_5$S$_3$ but also provides insights for manipulating its thermal and electronic properties for potential thermoelectric applications.

cond-mat.mtrl-sci↗