Calculated Lattice Thermal Conductivity Research Articles

Pressure induced mechanical, opto-electronics, and transport properties of ZnHfO3 oxide for solar cell and energy harvesting devices

Based on the density functional theory, we systematically investigate the effect of pressure on the mechanical, optoelectronic, and transport properties of ZnHfO3. The pressure has been employed up to 30 GPa in a step-size of 10 GPa. A slight variation in the lattice constant and Bulk modulus have been observed at the applied pressure steps. The electronic properties are significantly tuned by applying pressure. The calculated bandgap values slightly increase with increasing the pressure and its values start to decrease after the critical pressure of 20 GPa. More interestingly, a transition from indirect to direct band has been observed at the critical pressure. This transition of the bandgap is also justified by studying the optical properties like dielectric constant, refraction, and absorption at different pressure. Furthermore, we studied the electronic transport properties in terms of electrical conductivity, thermal conductivity, See-beck coefficient, and power factor at temperature (300–800 K). The calculated lattice thermal conductivities are low while the electrical conductivities and Seebeck coefficients are high at all pressure. Thus, the properties of the ZnHfO3 show high potential for thermoelectric applications.

First-Principles Study on Lattice Dynamics and Thermal Conductivity of Thermoelectric Intermetallics Fe3Al2Si3

Thermoelectric materials have been expected as a critical underlying technology for developing an autonomous power generation system driven at near room temperature. For this sake, Fe3Al2Si3 intermetallic compound is a promising candidate, though its high lattice thermal conductivity is a bottleneck toward practical applications. Herein, we have performed the first-principles calculations to clarify the microscopic mechanism of thermal transport and establish effective ways to reduce the lattice thermal conductivity of Fe3Al2Si3. Our calculations show that the lowest-lying optical mode has a significant contribution from Al atom vibration. It should correspond to large thermal displacements Al atoms. However, these behaviors do not directly cause an increase of the 3-phonon scattering rate. The calculated lattice thermal conductivity shows a typical temperature dependence and moderate magnitude. From the calculated thermal conductivity spectrum and cumulative thermal conductivity, we can see that there is much room to reduce the lattice thermal conductivity. We can expect that heavy-element doping on Al site and controlling fine microstructure are effective strategies to decrease the lattice thermal conductivity. This work suggests useful information to manipulate the thermal transport of Fe3Al2Si3, which will make this material closer to practical use.

Thermal transport property of novel two-dimensional nitride phosphorus: An ab initio study

Controlling thermal transport property is a crucial issue toward thermal management in two-dimensional (2D) materials. With first-principles calculations and Boltzmann transport equation (BTE), we have explored the thermal transport property of novel 2D nitride phosphorus (NP). We find that, at room temperature, the calculated lattice thermal conductivity (κlat) of novel 2D NP is 25.4 W/mK, being lower than that of buckled monolayer phosphorene, nitrogene, and β-NP. Through the analysis of corresponding phonon–phonon scattering channels (a + a ↔ o and a + o ↔ o), we find that the strong scatterings among acoustic phonons and low-frequency optical phonons are accountable for the low κlat of novel 2D NP. Additionally, we also study the sample size effects of novel 2D NP, which can further decrease κlat until a length of up to 5 μm. These results could provide valuable guidance to design the NP-based thermoelectric nano-devices and potential heat transport applications in other 2D materials.

Effect of Halogen Ions on the Low Thermal Conductivity of Cesium Halide Perovskite

The lattice dynamics of CsSnX3 (X = Cl, Br, and I) and CsPbI3, which are low-thermal-conductivity materials, are investigated using first-principles phonon calculations. Because of the strong lattice anharmonicity and the accompanying instability of high-temperature cubic phases, the self-consistent phonon theory, which can incorporate the effect of lattice anharmonicity at a mean-field level, is applied in this study. The calculated lattice thermal conductivity reproduced a low thermal conductivity, as shown experimentally, owing to the short phonon lifetime due to the incoherent scattering contribution of Cs atoms. The halogen ion dependence on thermal conductivity reveals that CsSnCl3 exhibits an anomalous lattice thermal conductivity that is as low as that of CsSnBr3. This indicates that the lattice dynamics cannot be explained merely in terms of the atomic mass of the compounds. The low thermal conductivity of CsSnCl3 is caused by the exceptionally short phonon lifetime; further, a bonding analysis suggests that covalent bonding contributes significantly to the unusual anharmonicity of CsSnCl3.

Quartic anharmonicity and ultra‐low lattice thermal conductivity of alkali antimonide compounds M 3 Sb ( M = K, Rb and Cs)

We investigate the role of the quartic anharmonicity in lattice dynamics and the thermal transport properties of the alkali antimonide compounds M3Sb (M = K, Rb and Cs) by using the self-consistent phonon theory combined with compressive sensing techniques. We found that the alkali-metal atoms in K3Sb, Rb3Sb and Cs3Sb have a strong quartic anharmonicity and play a crucial role in the lattice dynamic stability. Based on the above results, the thermal transport properties are estimated with the relaxation time approximation of Boltzmann transport equation, the calculated lattice thermal conductivity κL shows a remarkably low value at 300 K, which is 1.26, 0.63 and 0.52 Wm−1 K−1 for K3Sb, Rb3Sb and Cs3Sb, respectively. We have demonstrated the quartic anharmonicity of alkali antimonide compounds M3Sb (M = K, Rb and Cs) and studied their thermal transport properties, which has never been reported before, the ultra-low lattice thermal conductivity indicates that K3Sb, Rb3Sb and Cs3Sb are potential thermoelectric materials.

Low thermal conductivity and good thermoelectric performance in mercury chalcogenides

Thermoelectric (TE) property refers to converting thermal energy into electrical energy via Seebeck effect. Theoretically, the presence of a low thermal conductivity and a high thermoelectric power factor in a same material promises a good thermoelectric performance. In this paper, we investigate the thermal transport and thermoelectric properties of crystalline mercury chalcogenides (HgX, X = O, S, Se, Te) based on first-principles calculations combined with Boltzmann transport equation and electron–phonon interaction (EPI). Remarkably, the calculated lattice thermal conductivity κL of the semiconducting mercury chalcogenides (α-HgO and α-HgS) are fairly low (κL~0.60 W/mK at 300 K, which is about 38% of the value for the typical thermoelectric material PbTe), while the corresponding power factors S2σ for α-HgS are relatively high, which, as a result, leads to a good thermoelectric performance in α-HgS, with the thermoelectric figure of merit ZT even exceeding 1.28. However, the highest ZT of α-HgO is only 0.58 due to the relatively low S2σ. For comparison, the lattice thermal conductivity κL of the semimetallic mercury chalcogenides (β-HgS, β-HgSe, and β-HgTe) are much higher than that of PbTe, limiting the applications in thermoelectricity. These results indicate that semiconducting mercury chalcogenides may be potential candidates for the design of thermoelectric generators.

Thermoelectric properties of MoC monolayers from first-principles calculations

The thermoelectric properties of molybdenum monocarbide (MoC) monolayers, a new 2D material, are calculated from first-principles calculations using Boltzmann transport theory. The indirect bandgap of this monolayer semiconductor is 0.51 eV, and the calculated lattice thermal conductivity is 7.7 W/mK. The high Seebeck coefficient, indicating high thermoelectricity, is found in both p-type and n-type MoC monolayers. This coefficient increases with temperature. The electronic conductivity for the p-type is higher than for the n-type one because the valance band is much more delocalized than the conduction band around the Fermi level. However, the calculated electronic thermal conductivity is essentially independent of temperature. The thermoelectric figure of merit (ZT) value of the n-type doped 2D-MoC is smaller than that of the p-type; thus, the thermoelectric properties are dominated by the p-type.

Comprehensive first-principles study of bulk, bilayer, and monolayer α-PtO2 properties

Abstract We calculated the structural stability, electronic, optical, and thermoelectric properties for α-PtO2 structures (bulk, bilayer, and monolayer) via first-principles density functional theory calculations. The results show that there is good agreement between the calculated lattice parameters and the available experimental data for the bulk structure. The in-plane Young's modulus and Poisson's ratio were calculated in the harmonic elastic strain range, and the results show that the monolayer is harder than the bulk. GW0 calculations on top of a semi-local generalised gradient approximation for the exchange-correlation energy predicted that the bilayer, monolayer, and the bulk α-PtO2 are all semiconductors with indirect band gaps. The results reveal that the band gap increases from bulk to monolayer. Calculations of optical properties show that the monolayer can absorb up to 8% of incident radiation in the visible range, which is higher than the 2.3% for graphene of the same thickness. In contrast, the bulk absorbs 1.77%. Phonon calculations confirm that all structures are dynamically stable. To examine the lattice thermal conductivity, the Boltzmann transport equation calculations in conjunction with density functional theory were implemented. The in-plane calculated lattice thermal conductivity were 8.47 × 10−8Wm−1K−1 for bulk, 4.59 × 10−8Wm−1K−1 for bilayer and 1.06 × 10−8Wm−1K−1 per layer at 300 K. The obtained thermoelectric figure of merit (ZT) per layer were 0.11 for bulk, 0.62 for bilayer and 0.74 for monolayer, respectively. The investigation shows that the n-type in monolayer has the most promise for thermoelectric applications.

Capturing the nuclear quantum effects in molecular dynamics for lattice thermal conductivity calculations: Using ice as example.

Molecular dynamics (MD) is a powerful (and the most viable) tool to compute the thermal conductivities of solid disordered materials. However, conventional classical MD fails to describe the nuclear quantum effects (NQEs), so it may give inaccurate results for light materials at low temperatures. While the importance of NQE has been widely acknowledged, yet we do not have a fully reliable method to account for NQE in the MD thermal conductivity calculations. In this work, we will investigate and analyze the performances of a number of path-integral-based quantum MD methods, using ordered ice as a test case. To establish the validity of these methods, we will compare the MD results with the lattice dynamics results, in both classical and quantum limits. Through such a comparison, we will show that methods such as ring polymer MD stand as a good approach for a complex solid with short phonon lifetimes but could be problematic when describing long-living acoustic phonons. In addition, we will show that the rigid water model, which is the state-of-the-art model in the studies of ice/water systems, fails to capture most of the NQEs in ice thermal conductivity. Neglecting librational and translational NQEs leads to essential errors, which clearly demonstrates the importance of a true quantum simulation method that treats all modes at a consistent quantum level.

Low thermal conductivity and good thermoelectric performance in mercury chalcogenides

Thermoelectric (TE) property refers to converting thermal energy into electrical energy via Seebeck effect. Theoretically, the presence of a low thermal conductivity and a high thermoelectric power factor in a same material promises a good thermoelectric performance. In this paper, we investigate the thermal transport and thermoelectric properties of crystalline mercury chalcogenides (HgX, X = O, S, Se, Te) based on first-principles calculations combined with Boltzmann transport equation and electron–phonon interaction (EPI). Remarkably, the calculated lattice thermal conductivity κL of the semiconducting mercury chalcogenides (α-HgO and α-HgS) are fairly low (κL~0.60 W/mK at 300 K, which is about 38% of the value for the typical thermoelectric material PbTe), while the corresponding power factors S2σ for α-HgS are relatively high, which, as a result, leads to a good thermoelectric performance in α-HgS, with the thermoelectric figure of merit ZT even exceeding 1.28. However, the highest ZT of α-HgO is only 0.58 due to the relatively low S2σ. For comparison, the lattice thermal conductivity κL of the semimetallic mercury chalcogenides (β-HgS, β-HgSe, and β-HgTe) are much higher than that of PbTe, limiting the applications in thermoelectricity. These results indicate that semiconducting mercury chalcogenides may be potential candidates for the design of thermoelectric generators.

First-principles study on the structural, electronic, elastic and thermal properties of P42/mnm-BSi

Using first-principles density functional theory, a tetragonal silicon–boron binary structure with space group P42/mnm is predicted in present work. This structure is confirmed to be dynamically and mechanically stable below 19.3 GPa, and possesses lower energy than other candidates. Based on the plane wave pseudopotential method, the electronic structure, elastic constant, bulk modulus, shear modulus, Young’s modulus, lattice thermal conductivity and phonon lifetime of P42/mnm-BSi are systematically studied. Interestingly, a four-center and six-electron delocalized π bond is found in P42/mnm-BSi, which is the most important factor for its structural stability. The optical spectra calculations reveal that P42/mnm-BSi is a wide band-gap semiconductor with an indirect band-gap of 2.5 eV and has a promising application in the photoelectric devices. The calculated lattice thermal conductivity along the [001] crystal direction is 145 Wm−1 K−1 that is about three times higher than that along both the [100] and [010] directions, which is originated from the different group velocity along the crystal axis. Moreover, the acoustic–optical coupling has some positive influences on lattice thermal conductivity. This study gives a fundamental understanding of the structural, electronic, elastic and heat transport properties in P42/mnm-BSi.

A comprehensive study of phonon thermal transport in 2D IV-VI semiconductors MX (M = Ge, Sn; X = S, Se)

Based on the density functional theory and first-principles calculations we conducted a comprehensive study of the thermal transport properties of dynamical stable 2D IV-VI semiconductors MX (M = Ge, Sn; X = S, Se). The calculated lattice thermal conductivity is anisotropic, and the larger value of aaxis can be attributed to the higher phonon group velocity, besides, the optical modes of SnSe made a great contribution to the lattice thermal conductivity as a result of the most optical modes are located in the low frequency range. In addition, the lattice thermal conductivity of GeX is generally larger than that of SnX, which can be also attributed to the larger phonon group velocity. Our research reveals the thermal transport characteristics of 2D MX and points out the difference in lattice thermal conductivity of GeX and SnX.

First-principles calculation of lattice thermal conductivity and thermoelectric figure of merit in ferromagnetic half-Heusler alloy CoMnSb

Half-Heusler (HH) alloys are an important and well-studied class of thermoelectric, magnetic, and spintronic materials. However, few studies have reported on thermal conductivity of magnetic HH alloys. In this study, we have performed first-principles calculation of the thermoelectric properties of a magnetic HH alloy CoMnSb. The lattice thermal conductivity of CoMnSb was found to be smaller than typical nonmagnetic HH alloys (CoTiSb, CoZrSb). The reason for this was found to be the small group velocity and relaxation time of acoustic phonons. Moreover, we estimated the electronic thermal conductivity and power factor, and finally, we evaluated the thermoelectric figure of merit ZT of CoMnSb.

Lattice vibrational modes and phonon thermal conductivity of single-layer GaGeTe

Exploring the vibrational properties of experimental or theoretical finding of new phase two-dimensional (2D) materials is one key to expand their promising application. The GaGeTe monolayer with high carrier mobility, tunable band structure, and low cleavage energy attracts rapidly growing interests in electronics. However, their vibrational modes and phonon properties are not explored. Based on first-principles calculations within the framework of density functional perturbation theory, we systematically study the lattice vibrational modes as well as phonon thermal conductivity of single-layer GaGeTe, which could be exfoliated from the experimentally synthesized GaGeTe crystal. We find that the frequencies and intensities of A1g and Eg Raman modes, contributing to the main peaks in Raman spectra of monolayer GaGeTe, show distinct responses to different external strains. The calculated lattice thermal conductivity of GaGeTe is about 58 Wm-1 K−1, which is comparable to that of MoS2 (around 52 Wm−1K−1) and two orders of magnitude lower than that of graphene (2000 Wm−1K−1) at room temperature. This is mainly due to the partial couple for acoustic branches and low frequency optic phonon branches, moderate group velocity, strong anharmonic ZA phonon branch. Moreover, atom substitution at tellurium could be as an effective strategy to further decrease lattice thermal conductivity. Our findings fill in the gap about the thermal transport properties of GaGeTe monolayer and trigger for further experimental verification of the predicted properties.

Ab Initio Study on the Lower Mantle Minerals

Recent progress in theoretical mineral physics based on the ab initio quantum mechanical computation method has been dramatic in conjunction with the rapid advancement of computer technologies. It is now possible to predict stability, elasticity, and transport properties of complex minerals quantitatively with uncertainties that are comparable to or even smaller than those attached in experimental data. These calculations under in situ high-pressure ( P) and high-temperature conditions are of particular interest because they allow us to construct a priori mineralogical models of the deep Earth. In this article, we briefly review recent progress in studying high- P phase relations, elasticity, thermal conductivity, and rheological properties of lower mantle minerals including silicates, oxides, and some hydrous phases. Our analyses indicate that the pyrolitic composition can describe Earth's properties quite well in terms of density and P- and S-wave velocity. Computations also suggest some new hydrous compounds that could persist up to the deepest mantle and that the postperovskite phase boundary is the boundary of not only the mineralogy but also the thermal conductivity. ▪ The ab initio method is a strong tool to investigate physical properties of minerals under high pressure and high temperature. ▪ Calculated thermoelasticity indicates that the pyrolytic composition is representative to the chemistry of Earth's lower mantle. ▪ Simulations predict new dense hydrous phases stable in the whole lower mantle pressure and temperature condition. ▪ Calculated lattice thermal conductivity suggests a heat flow across the core mantle boundary no greater than 10 TW.

First-principles calculations of phonon transport in two-dimensional penta-X2C family

Two-dimensional (2D) materials exhibit enhanced thermoelectric (TE) performance compared to bulk materials, which relies heavily on lattice thermal conductivity. Penta-X2C (X = P, As, and Sb) is a newly predicted 2D material family with promising potential applications in photocatalytic water splitting and photovoltaic and optoelectronic devices. To achieve a combination of photovoltaic and TE technologies and further boost the energy utilization rate, in this paper, we systematically investigate the thermal transport of the penta-X2C family. Density functional theory combined with semiclassical Boltzmann transport approach was used to evaluate the thermal transport. Interestingly, the calculated lattice thermal conductivities (kl) of penta-Sb2C are two orders of magnitude smaller than that of penta-P2C, despite that they share similar atomic structure. The calculated kl of penta-P2C, penta-As2C, and penta-Sb2C are 75.27 W m−1 K−1, 19.11 W m−1 K−1, and 0.72 W m−1 K−1, respectively. Penta-Sb2C also exhibits low average acoustic group velocity, large Grüneisen parameters, strong optical–acoustic phonon coupling, and short phonon mean free path. These results qualify penta-Sb2C as a promising candidate for building outstanding TE devices.

Thermoelectric properties of doped β-InSe by Bi: First principle calculations

The thermoelectric properties are investigated for doped β-InSe alloy with Bi on Se site (β-InSe1-xBix; x = 0.0, 0.0625, 0.125, 0.1875, 0.25). The calculations are based on density functional theory (DFT) combined with the Boltzmann transport theory. The calculated formation energies and elastic constants confirmed the thermodynamic and mechanical stability of their crystal structure. A direct band gap of 0.73 eV is predicted for β-InSe, however, the structure becomes metallic upon doping with Bi. The increase of Bi concentration leads to an enhancement in the power factor. The calculated lattice thermal conductivity (κL) and the figure of merit (ZT) of β-InSe are in excellent agreement with the reported experimental results. The κL value is decreasing as a result of doping, which reduces to about 50% in the case of β-InSe0.75Bi0.25from that of β-InSe at 300 K. This leads to an enhancement in the ZT value to 0.65 at 800 K.

Thermal conductivity near the bottom of the Earth's lower mantle: Measurements of pyrolite up to 120 GPa and 2500 K

Knowledge of thermal conductivity of mantle minerals is crucial for understanding heat transport from the Earth's core to mantle. At the pressure-temperature conditions of the Earth's core-mantle boundary, calculations of lattice thermal conductivity based on atomistic models have determined values ranging from 1 to 14 W/m/K for bridgmanite and bridgmanite-rich mineral assemblages. Previous studies have been performed at room temperature up to the pressures of the core-mantle boundary, but correcting these to geotherm temperatures may introduce large errors. Here we present the first measurements of lattice thermal conductivity of mantle minerals up to pressures and temperatures near the base of the mantle, 120 GPa and 2500 K. We use a combination of continuous and pulsed laser heating in a diamond anvil cell to measure the lattice thermal conductivity of pyrolite, the assemblage of minerals expected to make up the lower mantle. We find a value of 3.9+1.4−1.1 W/m/K at 80 GPa and 2000 to 2500 K and 5.9+4.0−2.3 W/m/K at 124 GPa and 2000 to 3000 K. These values rule out the highest calculations of thermal conductivity of the Earth's mid-lower mantle (i.e. k<6 W/m/K at 80 GPa), and are consistent with both the high and low calculations of thermal conductivity near the base of the lower mantle.

Reduction in thermal conductivity of Sb2Te phase-change material by scandium/yttrium doping

Binary Sb2Te is considered as a potential recording material for phase-change memory due to its higher crystallization speed than the widely investigated ternary Ge-Sb-Te alloys. To further improve the performance of Sb2Te, various dopants such as scandium (Sc) have been explored. Yet, the thermal conductivity of the pristine and doped Sb2Te is unknown, even though the thermal conductivity (κ) is an essential parameter for phase change memory devices as thermal conductivity determines the exchange of energy with surroundings and heat transport in the SET/RESET process. In this work, by means of ab initio calculations, we have calculated the thermal conductivity of Sb2Te, scandium (Sc)-doped and yttrium (Y)-doped Sb2Te. The calculated lattice thermal conductivity values at 300 K are 3.76 Wm−1K−1, 3.22 Wm−1K−1 and 3.35 Wm−1K−1 for pristine Sb2Te, Sc-doped Sb2Te, and Y-doped Sb2Te, respectively, showing a reduction in lattice thermal conductivity by doping. Further analysis of the electron localization function and Bader charge distribution suggest that the increased bonding strength of the dopants with the surrounding atoms contributes to the reduction in lattice thermal conductivity of the doped Sb2Te. On the other hand, the electronic thermal conductivity of Sb2Te should also decrease due to the metal to semiconductor transition by Sc/Y doping as analyzed by the calculated density of states. Overall, the thermal conductivity of Sb2Te decreases to some extent by doping Sc and Y, which can lower the energy consumption and improve the efficiency of energy utilization in the data SET/RESET process and is thus desirable for phase-change memory devices.

Theoretical study of the electronic, thermodynamic, and thermo-conductive properties of γ-LiAlO2 with 6Li isotope substitutions for tritium production

Lithium aluminate has attracted researchers’ interests due to its wide applications. The structural, electronic, optical, lattice phonon thermodynamic, and thermo-conductive properties of γ-LiAlO2 with 6Li-isotope substitution are investigated by density functional theory and lattice phonon dynamics. The calculated results show that γ-LiAlO2 possesses a wide band-gap of 4.63 eV. The valence band is mainly formed by p orbitals of Li, O, and Al. The calculated lattice thermal conductivity of γ-LiAlO2 is found to be in good agreement over a wide range of temperatures with the available experimental data. The calculated dielectric matrix shows anisotropic behavior along z and x (or y) axes. Due to the wide band-gap, the optical conductivity of γ-LiAlO2 is mainly contributed from the electron hopping between valence-conduction bands. Substitution of 7Li with 6Li isotope in γ-LiAlO2 leads to observable differences in the lattice phonon frequencies at higher frequencies (>8 THz) and to slight changes in corresponding thermal conductivity and the infrared and Raman spectra which are in good agreement with our experimental measured data. The relevance of these properties for tritium production through 6Li absorbing neutron in nuclear reactors is discussed.