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Register a new userNonmonotonic strain dependence of lattice thermal conductivity in monolayer SiC: a first-principles study
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An increasing number of two-dimensional (2D) materials have already been achieved experimentally or predicted theoretically, which have potential applications in nano- and opto-electronics. Various applications for electronic devices are closely related to their thermal transport properties. In this work, the strain dependence of phonon transport in monolayer SiC with a perfect planar hexagonal honeycomb structure is investigated by solving the linearized phonon Boltzmann equation. It is found that room-temperature lattice thermal conductivity ($kappa_L$) of monolayer SiC is two orders of magnitude lower than that of graphene. The low $kappa_L$ is due to small group velocities and short phonon lifetimes, which can also be explained by polarized covalent bond due to large charge transfer from Si to C atoms. In considered strain range, it is proved that the SiC monolayer is mechanically and dynamically stable. With increased tensile strain, the $kappa_L$ of SiC monolayer shows an unusual nonmonotonic up-and-down behavior, which is due to the competition between the change of phonon group velocities and phonon lifetimes of low frequency phonon modes. At low strains ($<$8%), the phonon lifetimes enhancement induces the increased $kappa_L$, while at high strains ($>$8%) the reduction of group velocities as well as the decrease of the phonon lifetimes are the major mechanism responsible for decreased $kappa_L$. Our works further enrich studies on phonon transports of 2D materials with a perfect planar hexagonal honeycomb structure, and motivate farther experimental studies.
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In a latest experimental advance, graphene-like and insulating BeO monolayer was successfully grown over silver surface by molecular beam epitaxy (ACS Nano 15(2021), 2497). Inspired by this accomplishment, in this work we conduct first-principles based simulations to explore the electronic, mechanical properties and thermal conductivity of graphene-like BeO, MgO and CaO monolayers. The considered nanosheets are found to show desirable thermal and dynamical stability. BeO monolayer is found to show remarkably high elastic modulus and tensile strength of 408 and 53.3 GPa, respectively. The electronic band gap of BeO, MgO and CaO monolayers are predicted to be 6.72, 4.79, and 3.80 eV, respectively, using the HSE06 functional. On the basis of iterative solutions of the Boltzmann transport equation, the room temperature lattice thermal conductivity of BeO, MgO and CaO monolayers are predicted to be 385, 64 and 15 W/mK, respectively. Our results reveal substantial decline in the electronic band gap, mechanical strength and thermal conductivity by increasing the weight of metal atoms. This work highlights outstandingly high thermal conductivity, carrier mobility and mechanical strength of insulating BeO nanosheets and suggest them as promising candidates to design strong and insulating components with high thermal conductivities.
The promise enabled by BAs high thermal conductivity in power electronics cannot be assessed without taking into account the reduction incurred when doping the material. Using first principles calculations, we determine the thermal conductivity reduction induced by different group IV impurities in BAs as a function of concentration and charge state. We unveil a general trend, where neutral impurities scatter phonons more strongly than the charged ones. $text{C}_{text{B}}$ and $text{Ge}_{text{As}}$ impurities show by far the weakest phonon scattering and retain BAs $kappa$ values of over $sim$ 1000 $text{W}cdottext{K}^{-1}cdottext{m}^{-1}$ even up to high densities making them ideal n-type and p-type dopants. Furthermore, going beyond the doping compensation threshold associated to Fermi level pinning triggers observable changes in the thermal conductivity. This informs design considerations on the doping of BAs, and it also suggests a direct way to determine the onset of compensation doping in experimental samples.
The electronic and thermal transport properties have been systematically investigated in monolayer C$_4$N$_3$H with first-principles calculations. The intrinsic thermal conductivity of monolayer C$_4$N$_3$H was calculated coupling with phonons Boltzmann transport equation. For monolayer C$_4$N$_3$H, the thermal conductivity (k{appa}) (175.74 and 157.90 W m-1K-1 with a and b-plane, respectively) is significantly lower than that of graphene (3500 Wm$^{-1}$K$^{-1}$) and C3N(380 Wm$^{-1}$K$^{-1}$). Moreover, it is more than the second time higher than C$_2$N (82.88 Wm$^{-1}$K$^{-1}$) at 300 K. Furthermore, the group velocities, relax time, anharmonicity, as well as the contribution from different phonon branches, were thoroughly discussed in detail. A comparison of the thermal transport characters among 2D structure for monolayer C$_4$N$_3$H, graphene, C$_2$N and C$_3$N has been discussed. This work highlights the essence of phonon transport in new monolayer material.
The low thermal conductivity of piezoelectric perovskites is a challenge for high power transducer applications. We report first principles calculations of the thermal conductivity of ferroelectric PbTiO$_3$ and the cubic nearly ferroelectric perovskite KTaO$_3$. The calculated thermal conductivity of PbTiO$_3$ is much lower than that of KTaO$_3$ in accord with experiment. Analysis of the results shows that the reason for the low thermal conductivity of PbTiO$_3$ is the presence of low frequency optical phonons associated with the polar modes. These are less dispersive in PbTiO$_3$, leading to a large three phonon scattering phase space. These differences between the two materials are associated with the $A$-site driven ferroelectricity of PbTiO$_3$ in contrast to the $B$-site driven near ferroelectricity of KTaO$_3$. The results are discussed in the context of modification of the thermal conductivity of electroactive materials.
In a recent preprint Kong et al, arXiv:0902.0642v1 (2009) claimed to calculate the lattice thermal conductivity of single and bi-layer graphene from first principles. The main findings were that the Umklapp-limited thermal conductivity is only slightly higher than that of high-quality bulk graphite along the basal plane, and that it does not strongly depend on the number of atomic layers. Here we explain that the calculation of Kong et al used a truncation procedure with a hidden parameter, a cut-off frequency for the long-wavelength acoustic phonons, which essentially determined the final result. Unlike in bulk graphite, there is no physical justification for introducing the cut-off frequency for the long wavelength phonons in graphene. It leads to substantial underestimation of graphenes lattice thermal conductivity and a wrong conclusion about the dependence on the number of atomic layers. We outline the proper way for calculating the lattice thermal conductivity of graphene, which requires an introduction of other scattering mechanisms to avoid a logarithmic divergence of the thermal conductivity integral.
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