A theoretical investigation of the lead‐free double perovskites halides Rb₂XCl₆ (X = Se, Ti) for optoelectronic and thermoelectric applications

Abstract

In this study, structural, electronic, optical, thermoelectric, and thermodynamics properties of vacancy‐ordered double perovskites Rb2XCl6 (X = Se, Ti) were explored theoretically. The results revealed that Rb2SeCl6 and Rb2TiCl6 are indirect band gap (Eg) semiconductors with Eg values of 2.95 eV, and 2.84 eV respectively. The calculated properties (phonons, elastic constant, Poisson's ratio, and Pugh's ratio) revealed that both materials are dynamically and chemically stable and can exhibit brittle (Rb2SeCl6) and ductile (Rb2TiCl6) nature. From the analysis of optical parameters, it was noticed that the refractive index of the materials has a value of 1.5–2.0 where light absorption was found from the visible to the ultraviolet region. The thermoelectric properties determined by using the BoltzTrap code demonstrated that at room temperature, the Figure of merit (ZT) was found to be 0.74 and 0.76 for Rb2SeCl6 and Rb2TiCl6, respectively. Despite a moderate value of ZT in such materials, further studies might explore effective methods for tuning the electronic band gap and improving the thermoelectric response of the material for practical energy production applications.

Optoelectronic and thermoelectric properties of novel stable lead-free cubic double perovskites A2NaIO6 (A = Ca, Sr) for renewable energy applications

“…The positive values up to a wide range of energy reflect the semiconductor behavior of both DPs. 49 In some regions, ε 1 (0) has negative values. In these regions, a material behaves like a perfect metal.…”

Opto‐electronic and thermophysical characteristics of A2TlAgF6 (A = Rb, Cs) for green technology applications

“…It is confirmed that ionic bonding exists in these compounds by the positive Cauchy pressure values found for A 2 TlAgF 6 (A = Rb, Cs). Another crucial factor that can be used to alter material characteristics on the makeup of microcracks is elastic anisotropy (A) 57 . Anisotropic materials must be presumed if the unity value deviates.…”

“…The thermoelectric performance of the materials under investigation has been evaluated using the figure of merit ZT = σS 2 T / κ . For effective thermoelectric materials, high Seebeck coefficients ( S ) and electric conductivity ( σ ) are preferred, while low thermal conductivity ( κ ) is considered ideal 57 . In the current study, we use the BoltzTraP code that is applied under constant relaxation time approximation 41 .…”

Ba2MgXO6 (X = S, Se), Chalcogenide‐Based Double Perovskite Materials for Green Optoelectronics and Thermoelectric Applications

“…Also, this cubic phase is thermodynamically stable because the calculated values of formation energy (E f ) (Table 2) have the negative values according to the condition for thermodynamic stability. [33] The dynamical stability is another important criterion for use of a compound in the devicebased applications. Therefore, we examined the chalcogenidebased Ba 2 MgXO 6 for dynamical stability from phonon dispersion spectra, where, from these spectra in Figure 2, it can be seen that the phonon frequencies are positive throughout the considered Brillouin zone.…”