arXiv subjects

Sreerag Sundaram

Publications and source records attributed to Sreerag Sundaram.

4 recordsLinked to original sources

arXiv2026

First-Principles Prediction of Phonon-Mediated Infrared Optical Properties of WO$_3$ Polymorphs

Many crystals exhibit polymorphism, undergoing atomic rearrangements that result in unit cells belonging to different symmetry groups. These structural changes directly affect lattice vibration modes and consequently influence their mid-infrared optical properties. In this study, we use tungsten trioxide (WO$_3$) as a representative system, owing to its multiple temperature-dependent phases, to study the impact of polymorphism on mid-infrared optical behaviour. Using a fully first-principles approach, we investigate three phases of WO$_3$ and evaluate their mid-infrared optical properties. Significant differences are observed among the three crystallographic phases, demonstrating the potential of this methodology as a predictive tool for materials discovery and targeted design.

cond-mat.mtrl-sci↗

arXiv2026

A first-principles approach for predicting infrared optical properties of solids

We present a simplified formalism for predicting infrared optical constants from first-principles calculations. Addressing limitations of the widely used four-parameter semi-quantum Lorentz model, the proposed approach bridges the gap between the harmonic three-parameter model and full self-energy-based methods. By incorporating essential anharmonic effects including four-phonon scattering and phonon renormalisation, the model provides an efficient and accurate alternative while maintaining low computational cost. The frequency-dependent refractive indices of MgO and rutile TiO$_2$ are computed and compared with experimental data, demonstrating good quantitative agreement. The framework offers a practical approach for predicting optical properties of materials across a wide range of materials.

cond-mat.mtrl-sci↗

arXiv2024

Design of radiative cooling paint coating and insights into its sub-ambient cooling behaviour

Recent developments in radiative cooling technologies have primarily focused on affordable paint coatings that are easy to fabricate and deploy. Using a systematic approach to obtain optimal parameters, a radiative cooling (RC) paint coating using titanium dioxide (TiO2) and polydimethylsiloxane (PDMS) is designed. The resulting paint exhibits a high solar reflectivity of 88.2 % (more than 94% in visible and NIR) and an emissivity of 92.4 %. Outdoor testing demonstrates a maximum reduction of 7.9 0C in the internal temperature of an RC paint-coated aluminium (Al) box compared to a bare Al box but in contrast to other studies, no sub-ambient cooling have been observed. In this context, a comprehensive analysis explaining the absence of sub-ambient cooling and underscore the importance of a standardized reporting methodology for RC paints has been discussed. Theoretical calculations suggest that the developed RC paint can achieve sub-ambient cooling (1-4 0C) under specific ambient conditions.

physics.app-ph↗

arXiv2022

Achieving passive daytime radiative cooling via TiO$_2$/PDMS coating

The exponential growth in population and the increasing global temperature trickles down to an explosive demand in cooling and refrigeration. The vicious cycle of carbon footprint generation by these cooling devices can be broken by a mechanism of passive cooling. This study outlines research undertaken with the aim to design such materials - exhibiting high reflectance in the solar spectrum and high emission in the atmospheric transparency window of 8-13 $μ$m. The Monte Carlo (MC) method is used to simulate light propagation in a composite material aiding the design of metamaterials with these specific thermo-optical properties. A TiO$_2$/PDMS coating is fabricated to obtain > 91 \% solar reflectivity and > 75 \% emissivity in the atmospheric transparency window. This translates to cooling the coated body by 4-9 $^\circ$C below the ambient under peak solar irradiation in Mumbai, India. The facile fabrication process supplemented with the potential versatility of this coating shows promise to attain passive daytime radiative cooling on a commercial scale.

physics.app-ph↗