Vacancy-ordered double perovskites (A 2 BX 6 ), being one of the environmentally friendly and stable alternatives to lead halide perovskites, have garnered considerable research attention in the scientific community. However, their thermal transport has not been explored much, despite their potential applications. Here, we explore Cs 2 BI 6 (B = Pt, Pd, Te, Sn) as potential thermoelectric materials using state-of-the-art first-principles-based methodologies, viz., density functional theory combined with many-body perturbation theory (G 0 W 0 ) and spin−orbit coupling. The absence of polyhedral connectivity in vacancy-ordered perovskites gives rise to additional degrees of freedom, leading to lattice anharmonicity. The presence of anharmonic lattice dynamics leads to strong electron−phonon coupling, which is well-captured by the Froḧlich mesoscopic model. The lattice anharmonicity is further studied using ab initio molecular dynamics and the electron localization function. The maximum anharmonicity is observed in Cs 2 PtI 6 , followed by Cs 2 PdI 6 , Cs 2 TeI 6 , and Cs 2 SnI 6 . Also, the computed average thermoelectric figure of merit (zT) for Cs 2 PtI 6 , Cs 2 PdI 6 , Cs 2 TeI 6 , and Cs 2 SnI 6 is 0.88, 0.85, 0.95, and 0.78, respectively, which reveals their promising renewable energy applications.

Using first-principles calculations, we report the electronic properties with a special focus on the band splitting in the WSi2N4 class of materials. Due to the broken inversion symmetry and strong spin–orbit coupling, we detect coupled spin-valley effects at the corners of the first Brillouin zone (BZ). Additionally, we observe cubically and linearly split bands around the Γ and M points, respectively. The in-plane mirror symmetry (σ h ) and reduced symmetry of the arbitrary k -point, enforce the persistent spin textures (PST) to occur in full BZ. We induce the Rashba splitting by breaking the σ h through an out-of-plane external electric field (EEF). The inversion asymmetric site point group of the W atom introduces the hidden spin polarization in centrosymmetric layered bulk counterparts. Low energy k.p models demonstrate that the PST along the M–K line is robust to EEF and layer thickness, making them suitable for applications in spintronics and valleytronics.

Spin–orbit coupling (SOC) in conjunction with broken inversion symmetry acts as a key ingredient for several intriguing quantum phenomena, viz., Rashba–Dresselhaus (RD) effect. The coexistence of spontaneous polarization and the RD effect in ferroelectric (FE) materials enables the electrical control of spin degrees of freedom. Here, we explore the FE lead halide perovskite CsPbF3 as a potential candidate in the field of spintronics by employing state-of-the-art first-principles-based methodologies, viz., density functional theory (DFT) with semilocal and hybrid functional (HSE06) combined with SOC and many-body perturbation theory (G0W0). For a deeper understanding of the observed spin splitting, the spin textures are analyzed using the k.p model Hamiltonian. We find there is no out-of-plane spin component indicating that the Rashba splitting dominates over Dresselhaus splitting. We also observe that the strength of Rashba spin splitting can be substantially tuned on application of uniaxial strain (±5%). More interestingly, we notice reversible spin textures by switching the FE polarization in CsPbF3 perovskite, making it potent for perovskite-based spintronic applications.

This work demonstrates the photocatalytic N2 fixation ability of defect-engineered SrTiO3 and provides a stringent experimental protocol to avoid biases in the quantification of NH3 originated by surface contamination of working photocatalysts.

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