arXiv subjects

Tiantian Jia

Publications and source records attributed to Tiantian Jia.

4 recordsLinked to original sources

arXiv2025

Ultralow Lattice Thermal Conductivity Induced by Quasi-Chain Configuration in Rb2Se3

Alkali metal-based compounds have garnered significant attention due to their exceptionally low lattice thermal conductivity, which is crucial for applications in thermoelectric energy conversion and thermal barrier coatings. However, the fundamental mechanisms underlying such ultralow lattice thermal conductivity remain poorly understood. In this study, we investigate the intrinsic origins of the ultralow lattice thermal conductivity in the alkali metal-based ionic compound Rb2Se3, which exhibits a simple orthorhombic structure. By employing first-principles density functional theory (DFT) and solving the phonon Boltzmann transport equation (BTE), we reveal that Rb2Se3 achieves lattice thermal conductivity values below 0.2 W/mK along all crystallographic directions at 300 K. Our analysis uncovers a unique quasi-chain configuration within the crystal structure, characterized by strongly covalent Se-Se-Se trimers that act as localized rigid units, while Rb atoms occupy weakly bonded interstitial sites. This configuration induces pronounced anisotropy, weak bonding, and strong anharmonicity, leading to significant rattling-like behavior of all atoms and a dominance of low-frequency phonon modes. The interplay between the rigid Se trimers and the soft Rb matrix results in extreme phonon anharmonicity, as evidenced by large Gruneisen parameters and high atomic displacement parameters (ADPs). These findings provide a comprehensive understanding of the low lattice thermal conductivity in Rb2Se3 and establish a universal framework for designing low lattice thermal conductivity materials through the combination of rigid covalent clusters and soft ionic sublattices.

cond-mat.mtrl-sci↗

arXiv2022

Chemical trends in the high thermoelectric performance of the pyrite-type dichalcogenides: ZnS2, CdS2 and CdSe2

The thermoelectric properties of the three pyrite-type IIB-VIA2 dichalcogenides (ZnS2, CdS2 and CdSe2) are systematically investigated and compared with those of the prototype ZnSe2 in order to optimize their thermoelectric properties. Using the phonon Boltzmann transport equation, we find that they all have ultralow lattice thermal conductivities. By analyzing their vibrational properties, these are attributed to soft phonon modes derived from the loosely bound rattling-like metal atoms and to strong anharmonicities caused by the vibrations of all atoms perpendicular to the strongly bound nonmetallic dimers. Additionally, by correlating those properties along the series, we elucidate a number of chemical trends. We find that heavier atom masses, larger atomic displacement parameters and longer bond lengths between metal and nonmetal atoms can be beneficial to the looser rattling of the metal atoms and therefore lead to softer phonon modes, and that stronger nonmetallic dimer bonds can boost the anharmonicities, both leading to lower thermal conductivities. Furthermore, we find that all three compounds have complex energy isosurfaces at valence and conduction band edges that simultaneously allow for large density-of-states effective masses and small conductivity effective masses for both p-type and n-type carriers. Consequently, the calculated thermoelectric figures of merit (ZT), can reach large values both for p-type and n-type doping. Our study illustrates the effects of rattling-like metal atoms and localized nonmetallic dimers on the thermal transport properties and the importance of different carrier effective masses to electrical transport properties in these pyrite-type dichalcogenides, which can be used to predict and optimize the thermoelectric properties of other thermoelectric compounds in the future.

physics.app-ph↗

arXiv2019

Screening Promising Thermoelectric Materials in Binary Chalcogenides through High-Throughput Computations

The high-throughput (HT) computational method is a useful tool to screen high performance functional materials. In this work, using the deformation potential method under the single band model, we evaluate the carrier relaxation time and establish an electrical descriptor (\c{hi}) characterized by the carrier effective masses based on the simple rigid band approximation. The descriptor (\c{hi}) can be used to reasonably represent the maximum power factor without solving the electron Boltzmann transport equation. Additionally, the Grüneisen parameter (γ), a descriptor of the lattice anharmonicity and lattice thermal conductivity, is efficiently evaluated using the elastic properties, omitting the costly phonon calculations. Applying two descriptors (\c{hi} and γ) to binary chalcogenides, we HT compute 243 semiconductors and screen 50 promising thermoelectric materials. For these theoretically determined compounds, we successfully predict some previously experimentally and theoretically investigated promising thermoelectric materials. Additionally, 9 p-type and 14 n-type previously unreported binary chalcogenides are also predicted as promising thermoelectric materials. Our work provides not only new thermoelectric candidates with perfect crystalline structure for the future investigations, but also reliable descriptors to HT screen high performance thermoelectric materials.

cond-mat.mtrl-sci↗

arXiv2019

Excellent Thermoelectric Performances of Pressure Synthesized ZnSe2

We calculate the lattice thermal conductivities of the pyrite-type ZnSe2 at pressures of 0 and 10 GPa using the linearized phonon Boltzmann transport equation. We obtain a very low value [0.69 W/(mK) at room temperature at 0 GPa], comparable to the best thermoelectric materials. The vibrational spectrum is characterized by the isolated high-frequency optical phonon modes due to the stretching of Se-Se dimers and low-frequency optical phonon modes due to the rotation of Zn atoms around these dimers. The low-frequency optical phonon modes are characterized by a strong anharmonicity and will substantially increase the three-phonon scattering space which suppress the thermal conductivity. Interestingly, two transverse acoustic phonon modes with similar frequencies and wave vectors have very different degrees of anharmonicity depending on their polarization. We relate this to the low thermal conductivity and show that the anharmonicities of the transverse acoustic phonon modes are connected to the corresponding change in the pyrite parameter, which can be interpreted as a descriptor for the local volume change. To determine the thermoelectric performance of ZnSe2, we also investigate its electrical transport properties. The results show that both p-type or n-type ZnSe2 can show promising electrical transport properties. We trace this back to the complex energy isosurfaces of both valence and conduction bands. The low thermal conductivities and promising electrical transport properties lead to a large thermoelectric figure of merit of ZnSe2 for both p-type and n-type doping.

cond-mat.mtrl-sci↗