Unraveling the electronic, optical, ferroelectric, and electrocaloric properties of [formula omitted] thin film: Insight from first-principles effective Hamiltonian

Abstract

In this work, electronic, optical, dielectric and ferroelectric properties of PbxSr1-xTiO3 (PST) thin film are systematically investigated. This system is studied from first-principles computations using density functional theory (DFT) and effective Hamiltonian. In this regard, the influence of Pb doping on the above properties is elucidated to unravel a global description of this material. From the calculations along the higher symmetry direction, and upon substitution of Sr content, a direct band gap is obtained. Concerning the optical properties, the curves of refractive index revealed a systematic variation with composition. The results were compared with other reviews and showed a good agreement. Through a detailed analysis, investigations of several parameters are reported. However, an appropriate level of Pb doping can provide tremendous informations about this material, representing an important step toward deeper understanding for furthering knowledge, which may open the door for practical applications. This work reveals the contribution of Pb content especially on the phase transitions. The increase in the concentration of Pb shifts the critical temperature towards higher temperature and evolves the dipoles to switch for a large temperature range, resulting a large tetragonal (ferroelectric) phase and anomalous volume expansion, which in turn could improve the ferroelectric transition temperature. The dielectric constant, polarization and pyroelectric coefficient are examined as a function of the temperature. A typical hysteresis loops were clearly observed to confirm the ferroelectric-paraelectric phase transition. Besides, the electrocaloric effect (ECE) of PST thin film is also predicted with particular attention to the applied electric field and concentration x. Our calculations also revealed that PbxSr1-xTiO3 thin film exhibits a large room-temperature adiabatic temperature change (ΔT), which largely depends on the Pb content. The increase of Pb composition improves the adiabatic temperature change and enlarges its maximum at a relatively higher temperature. An enhancement regarding the ECE may potentially open the door for practical cooling device applications.