A systematic first-principles quantum analysis of the physical properties of Lead-Free bismuth titanate structures ABi4Ti4O15 (A = Ca, Ba) for low-cost green energy applications

We have investigated the optoelectronic and thermophysical properties of ABi₄Ti₄O₁₅ (A = Ba, Ca) using first principles DFT computations. The FP-LAPW technique employed in the WIEN2K code allows for accurate estimation of the ground state parameters of crystalline materials. The phonon spectra, formation energies, and other thermodynamic aspects of these layered perovskite materials indicate that they are thermodynamically stable. The analysis of energy band structures indicates that BaBi₄Ti₄O₁₅ and CaBi₄Ti₄O₁₅ are indirect semiconductors with energy band gaps of 1.89 eV and 1.76 eV, respectively.CaBi₄Ti₄O₁₅ has greater structural stability in comparison to BaBi₄Ti₄O₁₅.The analysis of optical characteristics reveals that these compounds exhibit high photon absorption in UV region. The static refractive index $n\left(\omega \right)$ values for BaBi₄Ti₄O₁₅ and CaBi₄Ti₄O₁₅ are 1.91 and 1.89, respectively. These values show optical activeness of these compounds since their $n\left(\omega \right)$ values fall within the range of 1.0 to 2.0. The figure of merit (ZT) values of 1.43 and 1.36 for BaBi₄Ti₄O₁₅ and CaBi₄Ti₄O₁₅, respectively, make them highly suitable for thermoelectric device applications.