Intrinsic Lattice Thermal Conductivity Research Articles

Thermal and thermoelectric transport measurements of an individual boron arsenide microstructure

Recent first principles calculations have predicted that boron arsenide (BAs) can possess an unexpectedly high thermal conductivity that depends sensitively on the crystal size and defect concentration. However, few experimental results have been obtained to verify these predictions. In the present work, we report four-probe thermal and thermoelectric transport measurements of an individual BAs microstructure that was synthesized via a vapor transport method. The measured thermal conductivity was found to decrease slightly with temperature in the range between 250 K and 350 K. The temperature dependence suggests that the extrinsic phonon scattering processes play an important role in addition to intrinsic phonon-phonon scattering. The room temperature value of (186 ± 46) W m−1 K−1 is higher than that of bulk silicon but still a factor of four lower than the calculated result for a defect-free, non-degenerate BAs rod with a similar diameter of 1.15 μm. The measured p-type Seebeck coefficient and thermoelectric power factor are comparable to those of bismuth telluride, which is a commonly used thermoelectric material. The foregoing results also suggest that it is necessary to not only reduce defect and boundary scatterings but also to better understand and control the electron scattering of phonons in order to achieve the predicted ultrahigh intrinsic lattice thermal conductivity of BAs.

Thermal properties of layered oxychalcogenides BiCuOCh (Ch = S, Se, and Te): A first-principles calculation

The phonon spectra, Debye temperatures, Grüneisen parameters, and the intrinsic lattice thermal conductivities of the layered oxychalcogenides BiCuOCh (Ch = S, Se, Te) have been studied with first-principles calculations. We find that the lattice thermal conductivities of them are anisotropic and quite low. The lowest thermal conductivity is only 0.14 Wm−1K−1 along c-axis for BiCuOTe. The size-dependent thermal conductivity of them is also discussed.

Exploration of the low thermal conductivities of γ-Y2Si2O7, β-Y2Si2O7, β-Yb2Si2O7, and β-Lu2Si2O7 as novel environmental barrier coating candidates

Thermal conductivities of γ-Y2Si2O7, β-Y2Si2O7, β-Yb2Si2O7, and β-Lu2Si2O7 were investigated by combined first-principles calculations and experimental evaluation. Theoretical calculation was used to predict the elastic properties, anisotropic minimum thermal conductivities, and temperature dependent lattice thermal conductivities. Experimentally, thermal conductivities of these disilicates were measured from room temperature to 1273K. In addition, their experimental intrinsic lattice thermal conductivities were determined from the corrected thermal diffusivity data after removing the extrinsic contributions from phonon scattering by defects and thermal radiation. The experimental lattice thermal conductivities match well with the theoretical predictions. Furthermore, Raman spectra of the disilicates was measured and used to estimate the optical phonon relaxation time. The present results clearly disclose the specific material parameters that determine the low thermal conductivity of RE2Si2O7 and may provide guidelines for the optimal thermal conductivity of rare earth disilicates.

Lattice thermal conductivity of penta-graphene

Motivated by the unique geometry and novel properties of penta-graphene proposed recently as a new carbon allotrope consisting of pure pentagons [Zhang et al. Proc. Natl. Acad. Sci. 2015, 112, 2372], we systematically investigated its phonon transport properties by solving exactly the linearized phonon Boltzmann transport equation combined with first principles calculations. The intrinsic lattice thermal conductivity Klat of penta-graphene is found to be about 645 W/mK at room temperature, which is significantly reduced as compared to that of graphene. The underlying reason is the strong anharmonic effect introduced by the buckled pentagonal structure with hybridized sp2 and sp3 bonding. A detailed analysis of the phonons of penta-graphene reveals that the ZA mode is the primary heat carrier (nearly 60%). The Klat is dominated by three-phonon scattering where the scattering rate of the Normal scattering process is comparable to that of the Umklapp scattering process. The phonon mean free path of the collective phonon excitations is in the order of micrometers. Complementing the high thermal conductivity of graphene, the low thermal conductivity of penta-graphene adds additional features to the family of carbon materials for thermal applications.

Towards intrinsic phonon transport in single‐layer MoS2

The intrinsic lattice thermal conductivity of MoS2 is an important aspect in the design of MoS2‐based nanoelectronic devices. We investigate the lattice dynamics properties of MoS2 by first‐principle calculations. The intrinsic thermal conductivity of single‐layer MoS2 is calculated using the Boltzmann transport equation for phonons. The obtained thermal conductivity agrees well with the measurements. The contributions of acoustic and optical phonons to the lattice thermal conductivity are evaluated. The size dependence of thermal conductivity is investigated as well. image

Thermoelectric properties of Ni-doped BaSi2

BaSi2 has been known as a wide gap semiconductor with an intrinsic low lattice thermal conductivity, therefore may be a promising environmental friendly thermoelectric (TE) material with abundant constituent elements. In this work, NixBa[Formula: see text]Si2 compounds with 0[Formula: see text] are synthesized by arc melting. The resistivity, thermal conductivity and Seebeck coefficient are measured in the temperature range of 300–850[Formula: see text]K. The resistivity of the undoped BaSi2 is as high as 480[Formula: see text]mOhm[Formula: see text]cm at room temperature. Through Ni-doping, both resistivity and the Seebeck coefficient decrease dramatically. Meanwhile, the total thermal conductivity has no apparent difference due to Ni-doping. The lattice thermal conductivity decreases with increasing temperature monotonously to be lower than 1[Formula: see text]W/m[Formula: see text]K at high temperatures.

Anisotropic lattice thermal conductivity in chiral tellurium from first principles

Using ab initio based calculations, we have calculated the intrinsic lattice thermal conductivity of chiral tellurium. We show that the interplay between the strong covalent intrachain and weak van der Waals interchain interactions gives rise to the phonon band gap between the lower and higher optical phonon branches. The underlying mechanism of the large anisotropy of the thermal conductivity is the anisotropy of the phonon group velocities and of the anharmonic interatomic force constants (IFCs), where large interchain anharmonic IFCs are associated with the lone electron pairs. We predict that tellurium has a large three-phonon scattering phase space that results in low thermal conductivity. The thermal conductivity anisotropy decreases under applied hydrostatic pressure.

Accurate Exploration of the Intrinsic Lattice Thermal Conductivity of Si2N2O by Combined Theoretical and Experimental Investigations

Si2N2O is a promising ceramic with various structural and functional applications. Precisely exploring its thermal conductivity is crucially important to evaluate its thermal transport reliability as high‐temperature structural component and electronic device. In this paper, temperature‐dependent lattice thermal conductivity of Si2N2O is studied based on a method integrating density functional theory calculations and experimental measurements. The relationship between the complex crystal structure (or heterogeneous chemical bonding) and lattice thermal conductivity of Si2N2O is studied. We herein show that Si2N2O intrinsically has moderately high lattice thermal conductivity [30.9 W·(m·K)−1 at 373 K], but extrinsic phonon scattering mechanisms, such as phonon scattering by point defects and grain boundaries etc., might significantly degrade the magnitude in experimental measurement [15.0 W·(m·K)−1 at 373 K]. This work suggests the significance that understanding the intrinsic thermal conductivity, namely the upper limit value, is a precursor to deciphering the more complicated heat transport behavior of Si2N2O.

Lattice vibration modes of the layered material BiCuSeO and first principles study of its thermoelectric properties

BiCuSeO has recently been shown to be one of the best oxide-based thermoelectric materials. The electrical properties of this material have been widely studied; however, the reasons for its intrinsically low thermal conductivity have only been briefly discussed. In this paper, we calculated the band structure and the electrical properties of BiCuSeO. The phonon spectrum, mode Grüneisen parameters and the thermal properties were also investigated. Additionally, we proposed a new method for illustrating the interlayer interactions in this material. For the first time, using first principles calculations, we provide direct evidence of the structural in-layer and interlayer off-phase vibration modes, which contribute to the anharmonic vibrations and structural scattering of phonons and result in an intrinsic low lattice thermal conductivity for BiCuSeO.

Linear correlation between Debye temperature and lattice thermal conductivity in II-VI and III-V semiconductors

A simple linear empirical relationship between high intrinsic lattice thermal conductivity K, and Debye temperature θa is suggested from data on high intrinsic lattice thermal conductivity K, and Debye temperature θa for some selected II-VI and III-V cubic zincblende type, and I-VII and II-VI rock-salt type binary semiconductors. A good linear correlation between Debye temperature and the high intrinsic lattice thermal conductivity was obtained. The minimum average percentage deviations in the present approach reveal that our simple model prove its identity and soundness compared to those of other author relations.

Effect of built-in-polarization field on intrinsic and extrinsic thermal conductivity of InN

The effect of built-in-polarization field on intrinsic and extrinsic lattice thermal conductivity of InN has been investigated theoretically. The built-in-polarization field modifies elastic constant, phonon velocity and Debye temperature of InN. Using these modified parameters, the relaxation time of phonons in various scattering processes at room temperature has been computed as a function of phonon frequency for with and without built-in-polarization field. The result shows that built-in-polarization field enhances the relaxation time of phonons. This implies longer mean free path of phonons. The Callaway model of phonon thermal conductivity has been used to estimate the effect of built-in-polarization field on intrinsic and extrinsic thermal conductivity of InN. The theoretical analysis shows that up to a certain temperature, the polarization field acts as negative effect and reduces the intrinsic and extrinsic thermal conductivity. However, after this temperature, both thermal conductivity are significantly contributed by polarization field. This gives the idea of temperature dependence of polarization effect, which signifies pyro-electric character of InN. The intrinsic thermal conductivity of InN at room temperature including built-in-polarization field is found to be enhanced by 28 %. However, at room temperature, the extrinsic thermal conductivity with built-in-polarization mechanism is found to be enhanced by 15 %. The method, we have developed may be taken in the simulation of heat transport in optoelectronic nitride devices to minimize the self-heating processes and in polarization engineering strategies to optimize the thermoelectric performance of InN alloys.

Low thermal conductivity of Lu4Si2O7N2: Theoretical and experimental studies

Thermal conductivity of bulk and dense oxynitride Lu4Si2O7N2 was measured at various temperatures. Results show that Lu4Si2O7N2 possesses low thermal conductivity and has potential applications as thermal insulation material. Detailed analysis shows that the experimental thermal diffusivity is significantly influenced by defects at low temperature and infrared radiation at high temperature. Therefore, we combined Debye model and Slack's equation to predict the temperature dependent intrinsic lattice thermal conductivity of Lu4Si2O7N2. All parameters indispensable in the calculation (equilibrium crystal structure, second order elastic constants, elastic modulus, Debye temperature, and Grüneisen constant) were predicted with the help of first-principles calculation methods. Finally, factors that influence the thermal conductivity of Lu4Si2O7N2 were discussed and possible explanations for the difference between experimental and theoretical thermal conductivity were illustrated.

Theoretical prediction and experimental determination of the low lattice thermal conductivity of Lu2SiO5

In this paper, Lu2SiO5 is reported as a promising rare-earth silicate with very low thermal conductivity. First-principle method is used to calculate the crystal structure, second order elastic constants and anisotropic elastic stiffness. Using these parameters, the whole profile of temperature dependent lattice thermal conductivity of Lu2SiO5 is predicted based on well-established models. The low lattice thermal conductivity of Lu2SiO5 originates from its complex crystal structure, significant bonding heterogeneity, low Debye temperature, and low sound velocity. Experimental intrinsic lattice thermal conductivity is also determined by successfully eliminating the extrinsic mechanisms for phonon scattering by point defects and grain boundaries, as well as the contribution of thermal radiation at high temperatures, from the measured lattice thermal diffusivity. The experimental result agrees well with theoretical prediction. The present method can illustrate how specific material parameters govern lattice thermal conductivity and provide quantitative guideline in searching novel candidates with low thermal conductivity.

Anisotropic intrinsic lattice thermal conductivity of phosphorene from first principles

Phosphorene, the single layer counterpart of black phosphorus, is a novel two-dimensional semiconductor with high carrier mobility and a large fundamental direct band gap, which has attracted tremendous interest recently. Its potential applications in nano-electronics and thermoelectrics call for fundamental study of the phonon transport. Here, we calculate the intrinsic lattice thermal conductivity of phosphorene by solving the phonon Boltzmann transport equation (BTE) based on first-principles calculations. The thermal conductivity of phosphorene at 300 K is 30.15 W m(-1) K(-1) (zigzag) and 13.65 W m(-1) K(-1) (armchair), showing an obvious anisotropy along different directions. The calculated thermal conductivity fits perfectly to the inverse relationship with temperature when the temperature is higher than Debye temperature (ΘD = 278.66 K). In comparison to graphene, the minor contribution around 5% of the ZA mode is responsible for the low thermal conductivity of phosphorene. In addition, the representative mean free path (MFP), a critical size for phonon transport, is also obtained.

Study of lattice vibration and thermal conductivity of BiCuSeO from first-principles calculations

ABSTRACTThe BiCuSeO has been proved to be one of the best oxide-based thermoelectric materials in recent years. Its electric properties have been widely studied, yet the lattice thermal conductivity was only discussed roughly. Our investigation suggests that the anharmonic vibration and the interlayer-interaction plays the crucial role in reducing the intrinsic lattice thermal conductivity. The thermal conductivity has been calculated based on quasi-harmonic approximation and detailed contribution have been discussed. The calculated data have good agreement with the experimental data.

Search for Organic Thermoelectric Materials with High Mobility: The Case of 2,7-Dialkyl[1]benzothieno[3,2-b][1]benzothiophene Derivatives

Control of doping is crucial for enhancing the thermoelectric efficiency of a material. However, doping of organic semiconductors often reduces their mobilities, making it challenging to improve the thermoelectric performance. Targeting on this problem, we propose a simple model to quantitatively obtain the optimal doping level and the peak value of thermoelectric figure of merit (zT) from the intrinsic carrier mobility, the lattice thermal conductivity, and the effective density of states. The model reveals that high intrinsic mobility and low lattice thermal conductivity give rise to a low optimal doping level and a high maximum zT. To demonstrate how the model works, we investigate, from first-principles calculations, the thermoelectric properties of a novel class of excellent hole transport organic materials, 2,7-dialkyl[1]benzothieno[3,2-b][1]benzothiophene derivatives (Cn-BTBTs). The first-principles calculations show that BTBTs exhibit high mobilities, extremely low thermal conductivities (∼0.2 W m...

Theoretical Predictions on Elastic Stiffness and Intrinsic Thermal Conductivities of Yttrium Silicates

Yttrium silicates are promising candidates for environmental and thermal barrier coatings owing to their excellent high‐temperature performances. Previous works have experimentally attested to their low thermal conductivity, nevertheless, the experimental data were significantly affected by measurement inaccuracy and the existence of defects such as point defects, dislocations, grain boundaries, and pores in measured samples. In this study, the temperature dependences of intrinsic lattice thermal conductivities of γ‐Y2Si2O7 and Y2SiO5 are predicted based on the first‐principles calculations of crystal structure, elastic moduli, Debye temperature, and Grüneisen constant. Both silicates display very low thermal conductivities over the range of 300–2000 K; and in addition, Y2SiO5 exhibits relatively lower thermal conductivity than γ‐Y2Si2O7. We also show certain discrepancies between experimental and theoretical thermal conductivities, and it strengthens the important role of theoretical prediction of intrinsic lattice thermal conductivities of promising materials.

Diameter dependence of carbon nanotube thermal conductivity and extension to the graphene limit

Using an exact numerical solution of the phonon Boltzmann equation, we demonstrate a nontrivial evolution with diameter of the intrinsic lattice thermal conductivity, $\ensuremath{\kappa}$, of a wide range of achiral and chiral single-walled carbon nanotubes (SWCNTs) into that of graphene, ${\ensuremath{\kappa}}_{graphene}$. We find that $\ensuremath{\kappa}<{\ensuremath{\kappa}}_{graphene}$ for all but the smallest diameter SWCNTs and that $\ensuremath{\kappa}$ exhibits a minimum for modest diameters. This behavior results because the inherent curvature in SWCNTs violates a selection rule in graphene arising from its reflection symmetry, which strongly restricts phonon-phonon scattering in that system.

Determination of the intrinsic temperature dependent thermal conductivity from analysis of surface temperature of laser irradiated materials

An experimental and analytical approach is described to determine the temperature dependent intrinsic lattice thermal conductivity, k(T), for a broad range of materials. k(T) of silica, sapphire, spinel, and lithium fluoride were derived from surface temperature measurements. Surfaces were heated from room temperature up to 3000 K using a CO2-laser irradiance ≤5 kW/cm2. The solution of the nonlinear heat flow equation was used to extract parameters of k(T)=A×Tε, where −1.13≤ε≤0 depending on the material. Results generally show good agreement with reported k(T). Below evaporation, the phonon-only k remains the dominant heat transport mechanism during laser heating.

Lattice thermal conductivity of single-walled carbon nanotubes: Beyond the relaxation time approximation and phonon-phonon scattering selection rules

We present a theoretical description of phonon thermal transport and intrinsic lattice thermal conductivity in single-walled carbon nanotubes (SWCNTs). An exact solution of the phonon Boltzmann equation is implemented using an efficient scheme that allows consideration of SWCNTs with a wide range of radii and chiralities. Our approach combines for the first time calculations of the full spectrum of anharmonic three-phonon scattering processes in SWCNTs with use of the correct selection rules that severely restrict the phase space of this scattering. In particular, we demonstrate that if only the acoustic phonon branches are considered, no umklapp scattering can occur: scattering of acoustic phonons by optic phonons is required to produce thermal resistance in SWCNTs. We also show that the commonly used relaxation time approximation gives a particularly poor description of thermal transport in SWCNTs because of the unusually weak phonon-phonon umklapp scattering in these systems.