Anharmonic phonons and anomalous thermal expansion of graphite

Mittal, R.; Singh, Bhanu Pratap; Mishra, S. K.; Chaplot, S. L.

doi:10.1016/j.ssc.2021.114324

Cited by 2 publications

(4 citation statements)

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“…Note that for the in-plane isotropic structure, we adopt the biaxial strain method, which can effectively reduce computational costs. 55,96 The Gruneisen parameters are obtained by expanding/ compressing lattice parameters with the strain ε = ±1%.…”

Section: Methodsmentioning

confidence: 99%

“…The axial generalized Grüneisen parameter γ j GT ( T ) can be expressed as , γ j GT ( T ) = 1 C V ( T ) ∑ boldq , ν γ q , ν j C q , ν The mode Grüneisen parameter γ q ,ν j and the mode specific heat C q ,ν can be obtained with uniaxial deformations. Note that for the in-plane isotropic structure, we adopt the biaxial strain method, which can effectively reduce computational costs. , The Grüneisen parameters are obtained by expanding/compressing lattice parameters with the strain ε = ±1%.…”

Section: Methodsmentioning

confidence: 99%

“…In contrast, the in-plane cases are subtler; e.g., some transition-metal dichalcogenides exhibit in-plane positive thermal expansion (PTE), whereas graphite and h -BN both show in-plane negative thermal expansion (NTE). − A popular explanation based on the anharmonicity of lattice vibrations is responsible for normal PTE, i.e., that most materials expand upon heating. − However, this theory cannot account for the abnormal NTE materials; their volumes tend to contract upon heating within a certain temperature range. Recently, TE anisotropy has attracted considerable attention due to the discovery of materials with peculiar PTE or NTE along one or two axes. − It has been demonstrated that the in-plane NTE of graphite and h -BN originates from the negative Grüneisen parameters, which are mainly determined by the low-frequency out-of-plane phonon modes. ,,− Intriguingly, SnSe with all positive Grüneisen parameters shows unusually uniaxial NTE along the armchair direction, which introduces another important factor, elastic property, in determining its TE behavior. − The cause of in-plane NTE can be explained with a suitable theoretical model. The original numerical model to describe the TE was proposed by Grüneisen in 1912, which built the relationship between phonons and TE .…”

Section: Introductionmentioning

confidence: 99%

“…The structural feature of layered materials, strong in-plane covalent bonding in atomic layers and van der Waals interaction between adjacent layers, determines thermal expansion (TE) anisotropy, which is one of the challenges in thermal management. − The TE along the out-of-plane direction of layered materials is usually positive because the atomic mean free path of adjacent layers increases faster during the expansion than that during the compression upon heating. In contrast, the in-plane cases are subtler; e.g., some transition-metal dichalcogenides exhibit in-plane positive thermal expansion (PTE), whereas graphite and h -BN both show in-plane negative thermal expansion (NTE). − A popular explanation based on the anharmonicity of lattice vibrations is responsible for normal PTE, i.e., that most materials expand upon heating. − However, this theory cannot account for the abnormal NTE materials; their volumes tend to contract upon heating within a certain temperature range. Recently, TE anisotropy has attracted considerable attention due to the discovery of materials with peculiar PTE or NTE along one or two axes. − It has been demonstrated that the in-plane NTE of graphite and h -BN originates from the negative Grüneisen parameters, which are mainly determined by the low-frequency out-of-plane phonon modes. ,,− Intriguingly, SnSe with all positive Grüneisen parameters shows unusually uniaxial NTE along the armchair direction, which introduces another important factor, elastic property, in determining its TE behavior. − The cause of in-plane NTE can be explained with a suitable theoretical model.…”

Section: Introductionmentioning

confidence: 99%

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Evaluating In-Plane Thermal Expansion of Two-Dimensional Layered Materials via Effective Descriptors

Zhang

Sun

et al. 2023

J. Phys. Chem. C

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Two-dimensional layered materials show promising applications in miniaturized devices, such as transistors, spintronics, and field emitters. However, substantial thermal management issues, including thermal mismatch and thermal stress, may degrade device performance. To address such challenges, the thermal expansion (TE) anisotropy determined by the structure feature of layered material needs to be well understood. Here, we propose two new descriptors to evaluate the TE behavior of layered materials, namely the axial elastic deviation factor σ i and the axial net thermal stress f i along the ith direction. The former, defined as the normalized elastic element difference of material elastic tensor C and compliance tensor S, can distinguish whether the thermal expansion of a material is driven by phonons (with small σ i ) or elastic property (with large σ i ) with few computational costs. The latter, axial stress (in GPa/K) induced by temperature, shows an accurate determination of the positive or negative thermal expansion along different in-plane directions of layered materials. Based on the analysis of descriptors, we found that PtS2 and PtSe2 are featured with a larger axial elastic deviation factor (>23%). Considering the elastic property, we for the first time report the in-plane negative thermal expansion in PtS2 (−1.2 ppm/K) and PtSe2 (−0.8 ppm/K). Our work provides a unified understanding of TE causes of layered materials via effective descriptors, which can serve as a guideline for high-throughput screening of thermal expansion materials and subsequent device design.

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Section: Methodsmentioning

confidence: 99%