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Comprehending the relationship between crystal structures and transport properties is crucial to develop materials with improved electrical and thermal properties for thermoelectric applications. In this article, we report on the complex crystal structure and physical properties of Cr2Sn3S7, a n-type magnetic semiconductor with a low energy band gap and low thermal conductivity. Importantly, we demonstrate that the high level of structural complexity is related to the coexistence of two sublattices: a host lattice, [Cr4Sn2S11]2–, characterized by a mixed Sn4+/Cr3+occupancy of its cationic sites, and a guest lattice characterized by [Sn4S3]2+chains, containing Sn2+cations only, closely related to the ones encountered in the orthorhombic SnS compound. By combining experiments including X-ray diffraction with ab initio calculations of electrons and phonons, we succeeded to elucidate the origin of the low thermal conductivity in Cr2Sn3S7.We demonstrate that the low dimensionality of the [Sn4S3]2+chains, which generates weak Sn···S interactions with the 3D host lattice, is induced by the lone pair stereochemical activity of Sn2+. This lattice softening favors strong anisotropic vibrations at low frequencies, highlighting the primordial role played by Sn2+cations in both crystal structure dimensionality and low thermal conductivity in tin-based sulfides.

Understanding the mechanisms that connect heat transport with crystal structures is fundamental to develop materials with optimized electrical and thermal properties for thermoelectric applications. In this work, we synthesized a series of bulk Cl-doped PbBi2S4by mechanical alloying combined with spark plasma sintering. A detailed structural analysis of PbBi2S4(m= 1 member of the series PbmBi2S3+m) and of the compounds Bi2S3(m= 0) and Pb3Bi2S6(m= 3) shows that the low dimensionality of their frameworks is induced by the stereochemical activity of Bi3+and Pb2+6s2lone pairs (L) and is mainly governed by the presence of BiS3L chains of tetrahedrons. By combining experiments with the ab initio band structure and phonon calculations, we discuss the structure-thermoelectric property relationships and clarify the interesting crystal chemistry in this system. We demonstrate that the ultralow thermal conductivity of these sulfides originates from the prominent 1D character induced by the bismuth chains in these frameworks, leading to weak interchain interactions compared to their strong intrachain bonds.

Earth-abundant silicon-, phosphorus-, and sulfur-related compounds are crucial for optoelectronic application. Specifically, experimentally proven monolayer SiP has attracted a great deal of attention in above listed field owing to its unique properties but is plagued with challenges such as photocorrosion and poor charge separation. Moreover, theoretical understanding on the relationship of the interface and photocatalytic activity in SiP-based chemicals is not well understood. In this work, hybrid functional first-principles calculations were used to explore the photocatalytic hydrogen evolution activity of SiP–PtS2heterostructure. Further examination of phonon, ab initio molecular dynamics (AIMD), and elastic property simulations confirms its dynamical stability. Its computed band gap of 1.59 eV is suitable for maximizing solar energy conversion efficiency, with noticeable strong absorption coefficients of 105cm–1order across visible–ultraviolet domains, asymmetric decent carrier mobility (∼103cm2V–1s–1), and low exciton binding energy (0.56 eV). Differences in charge density and Bader and Mulliken population analyses reveal that charge flows from the SiP to the PtS2layers, performing the dual functions of segregating photoinduced charge carriers and increasing their lifetimes. The relative band alignment of the monolayers promotes a spatial separation of the charges. An important feature of this heterostructure is that the band edges cross the water redox potential at pH of 0 upon −2% of compressive biaxial straining, with ΔGfor hydrogen evolution reaction (HER) barrier lower than −0.2 eV. The quadratic relationship between biaxial strain and atomic energy indicates that both the system and strains are elastic. Redox thermodynamic analysis predicts facile hydrogen production on the heterostructure. In particular, the calculated maximum solar power conversion efficiency (PCE) and solar-to-hydrogen (STH) efficiency can reach 22.9 and 23.8%, respectively.