Development of a Debye heat capacity model for vibrational modes with a gap in the density of states

Schliesser, Jacob; Woodfield, Brian F.

doi:10.1088/0953-8984/27/28/285402

Cited by 35 publications

(27 citation statements)

References 65 publications

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“…For C/SiC composites, the lattice vibrations of the matrix and carbon fiber would play important roles in heat conduction, mainly carried by phonon. According to the kinetic theory, the thermal conductivity ( k ) can be expressed following Equation 25 :

κ = \frac{1}{3} C ∙ \bar{v} ∙ l

where C represents the specific heat capacity,

\overset{v}{true}

is the average velocity of the phonon, and l denotes the total mean free path of phonons.…”

Section: Resultsmentioning

confidence: 99%

Section: Thermal Conductivity Of C/sic Composites With Mpcf Micro-pmentioning

confidence: 99%

“…26,27 As a result, the thermal conductivity was mainly related to the specific heat capacity and total mean free path. According to the Debye heat capacity model, 25,27 heat capacity should almost be constant above the Debye temperature of the material while it would vary with temperature under the Debye temperature. As shown in Figure 6B, the specific heat capacity increased with temperature.…”

Section: Thermal Conductivity Of C/sic Composites With Mpcf Micro-pmentioning

confidence: 99%

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Effect of initial density on thermal conductivity of new micro‐pipeline heat conduction C/SiC composites

et al. 2020

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Two-dimensional C/SiC composites have attracted increasing interests in recent years due to their low densities, high specific strengths, 1 elevated specific module, 2 and noncatastrophic mode of failure, 3 which made them promising thermal structural materials for applications in aerospace, aircraft braking, and space detection. 1,4,5 However, these harsh environments require them possessing not only thermal structural performances like load resistance, 2 but also functional properties such as high thermal conductivity, especially in thickness direction of the composites (about 5-12 W•m −1 •K −1 for now). 6-9 Therefore, C/SiC composites cannot serve as a functional materials for aerospace vehicle thermal discharge

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κ = \frac{1}{3} C ∙ \bar{v} ∙ l

where C represents the specific heat capacity,

\overset{v}{true}

is the average velocity of the phonon, and l denotes the total mean free path of phonons.…”

Section: Resultsmentioning

confidence: 99%

Section: Thermal Conductivity Of C/sic Composites With Mpcf Micro-pmentioning

confidence: 99%

Section: Thermal Conductivity Of C/sic Composites With Mpcf Micro-pmentioning

confidence: 99%

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Effect of initial density on thermal conductivity of new micro‐pipeline heat conduction C/SiC composites

et al. 2020

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“…vacancies) in insulating materials [26], and the B 3 , B 5 , B 7 , and B 9 terms represent the harmonic-lattice expression [27]. We note that these samples also exhibit a slight contribution from low-energy modes with a gap in the density of states, but these fits and their interpretation have been published elsewhere [28]. The fitting parameters, % RMS, and ranges of validity for these fits as well as those for the mid-and high-temperature regions are given in table 6.…”

Section: Heat Capacity Curve Fittingmentioning

confidence: 93%

Heat capacities, standard entropies and Gibbs energies of Sr-, Rb- and Cs-substituted barium aluminotitanate hollandites

Schliesser

Woodfield

et al. 2016

The Journal of Chemical Thermodynamics

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a b s t r a c t were measured from T = (2 to 300) K using a Quantum Design Physical Property Measurement System (PPMS). From the heat capacity results, the following thermodynamic parameters have been determined. The characteristic Debye temperatures H D over the temperature range (30 to 300) K of Sr-, Rb-, and Cs-hollandite are T = (178.2, 189.7, and 189.2) K, respectively, and their standard entropies at T = 298.15 K are (413.9 ± 8.3), (415.1 ± 8.3), and (419.6 ± 8.4) J Á K À1 Á mol À1 . Combined with previously reported formation enthalpies, their corresponding Gibbs energies of formation from oxides (D f G ox°) are (À194.9 ± 11.4), (À195.0 ± 12.8), and (À201.1 ± 12.8) kJ Á mol À1 , and those from elements (D f G el°) are (À7694.6 ± 12.5), (À7697.0 ± 13.9), and (À7697.1 ± 13.9) kJ Á mol À1 at T = 298.15 K. The similarities among the obtained D f G ox°v alues suggest that the three substituted hollandites have similar thermodynamic stabilities at standard conditions, which is in agreement with the ease of Cs-Rb-Sr substitutions in the hollandite structure.

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“…For these materials, a one-dimensional gapped model was used. More information of these gapped models can be found in [47]. The fitting parameters, % RMS, and ranges of validity for these fits as well as those of the mid and high temperature regions are given in Table 13.…”

Section: Heat Capacity Curve Fittingmentioning

confidence: 99%

Heat capacities, entropies, and Gibbs free energies of formation of low-k amorphous Si(O)CH dielectric films and implications for stability during processing

Chen

Calvin

Asplund

et al. 2019

The Journal of Chemical Thermodynamics

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a b s t r a c tLow-temperature heat capacities of a series of low dielectric constant amorphous films with different compositions were measured from 1.8 to 300 K using a Quantum Design Physical Property Measurement System (PPMS). By using piece wise functions to fit the heat capacities, the characteristic Debye temperatures H D and the standard molar entropies are determined. The standard molar entropies of these materials range from 8.8 JÁK À1 Ámol À1 to 17.5 JÁK À1 Ámol À1 . Together with the formation enthalpies obtained by high temperature oxidative solution calorimetry in molten sodium molybdate solvent, the corresponding Gibbs free energies from elements and crystalline constituents (and gaseous products as required) are obtained. The Gibbs free energy terms of these materials are dominated by the enthalpy term rather than the entropy. These samples are thermodynamically stable at room temperature with respect to elements and the samples with oxygen incorporated are generally thermodynamically more stable than the others. However, compared to crystalline binary counterparts and gases, some of these materials possess either positive or close-to-zero Gibbs free energies of formation, indicating that they are thermodynamically metastable; while, for the rest, which are stable at ambient conditions, elevation of temperature will eventually lead to decomposition.

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Development of a Debye heat capacity model for vibrational modes with a gap in the density of states

Cited by 35 publications

References 65 publications

Effect of initial density on thermal conductivity of new micro‐pipeline heat conduction C/SiC composites

Effect of initial density on thermal conductivity of new micro‐pipeline heat conduction C/SiC composites

Heat capacities, standard entropies and Gibbs energies of Sr-, Rb- and Cs-substituted barium aluminotitanate hollandites

Heat capacities, entropies, and Gibbs free energies of formation of low-k amorphous Si(O)CH dielectric films and implications for stability during processing

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