Quantitatively revealing the specific heat capacity evolution in PbI ₂

Abstract PbI ₂ , a typical 2D layered semiconductor in the metal halide family, has attracted extensive attention for its unique physical properties and promising applications in the energy field, elucidating the evolution of its specific heat capacity and the quantitative contributions of lattice vibrations (phonons) and electronic contribution is critical for accurately predicting and regulating its thermal behavior. Herein, we combined experimental characterizations and density functional theory calculations to systematically dissect the temperature-dependent changes in phonon and electronic specific heat capacities of PbI ₂ over the range of 100 K to 300 K. With increasing temperature, the molar phonon specific heat capacity rises continuously from 62.13 J (mol·K) ⁻¹ (100 K) to 69.72 J (mol·K) ⁻¹ (300 K), and its proportion in the total specific heat capacity increases gradually from 88.42% to 91.31%. Meanwhile, the electronic density of states at the valence band maximum decreased by a factor of 1.5, resulting in a notable reduction in the molar electronic specific heat capacity from 1.87 J (mol·K) ⁻¹ to 0.83 J (mol·K) ⁻¹ , with its proportion in total specific heat capacity, dropping from 2.66% to 1.09%. Our results demonstrate that lattice vibrations are the dominant contributor to the specific heat capacity of PbI ₂ in the 100–300 K range, while the electronic contribution, though secondary, is non-negligible and exhibits distinct temperature dependence.