Lattice vibrations and thermal properties of carbon nitride with defect ZnS structure from first-principles calculations

Abstract

The phonon spectrum of C 3 N 4 with defect zincblende-type structure (δ-C 3 N 4 ) was calculated by density functional theory (DFT) techniques. The results permit an assessment of important mechanical and thermodynamical properties such as the bulk modulus, lattice specific heat, vibration energy, thermal expansion coefficient, and thermal Grüneisen parameter. The thermal Grüneisen parameter of δ-C 3 N 4 is calculated to be about 1.19 at 300 K, comparable to that of diamond. The coefficient of linear thermal expansion of this structure is calculated to be about 2.2 × 10 −6 K −1 at room temperature. The thermal conductivity coefficient of δ-C 3 N 4 is also estimated using Slack's theory to be as high as about 216 W m −1 K −1 .

Thermodynamic properties of Mg2Si and Mg2Ge investigated by first principles method

“…In the quasi-harmonic approximation, the temperature dependent Helmholtz free energy F(V,T) can be written as [14]:…”

“…In practice, they were often derived from the experimental heat capacity and thermal expansion coefficient, respectively. Since the experimental data are not always available, it is desirable to predict the parameters systematically from some sort of theoretical calculations [13,14].…”

Stability, structure and electronic properties of γ-Fe23C6 from first-principles theory

“…This indicates that in the discussion of formation of the compounds one must consider the difference in the entropies of lattice vibration at the formation temperature (T $ 500-1200 K), while the entropy from (chemical and structural) defects in the lattices can be ignored [49][50][51]. Therefore, a complete understanding about the stability of c-Fe 23 C 6 requires not only the formation enthalpy at 0 K and 0 Pa, but also the lattice vibration (phonon spectrum), and even the magnon-phonon coupling at the formation temperature.…”

Predicting Physical Properties of Tetragonal, Monoclinic and Orthorhombic M 3 N 4 ( M =C, Si, Sn) Polymorphs via First-Principles Calculations

“…The 𝛼 phase is closely related to the low-temperature 𝛽 phase, while it is generally believed to be the metastable phase. [9] Fang et al [10] have calculated the phonon spectrum, thermal expansion, specific heat and free energy of zincblende-type C 3 N 4 (𝐹 4 3𝑚) through the VASP code. Several thermodynamic properties of 𝛼-, 𝛽-, and 𝛾-Si 3 N 4 have been studied in the previous works.…”