Bulk β-SrZrS3 sulfide perovskite: A mechanically robust platform with thermoelectric potential beyond thin-film optoelectronics

Sulfide perovskites have shown great promise in thin-film optoelectronics, but their versatile potential for sustainable energy applications is severely limited by the lack of mechanical and transport parameters in bulk materials. Here, we address these challenges by presenting a systematic investigation of the mechanical and thermoelectric properties of three-dimensional distorted perovskite β-SrZrS3 in bulk form. First-principles calculations predict multiple conduction band valleys and intrinsic lattice anharmonicity in β-SrZrS3, suggesting a favorable thermoelectric potential. We develop an economical and scalable synthesis route involving sulfurization of SrZrO3 powders followed by fast spark plasma sintering, yielding high-quality, crack-free centimeter-scale β-SrZrS3 bulks with ∼100% relative density. The bulks exhibit excellent mechanical properties including a Vickers hardness of ∼1.75 GPa, a Young's modulus of 91.7 GPa, and high fracture resistance, enabling practical machining and device integration. The pristine β-SrZrS3 sample exhibits a combination of a large Seebeck coefficient of −435.7 μV K−1, high electron mobility of 196.6 cm2 V−1 s−1, and low lattice thermal conductivity of 2.2 W m−1 K−1 at room temperature. To further enhance the thermoelectric performance, the strategy of constructing a metallic copper intergranular network is proposed, which achieves a 30-fold enhancement in carrier concentration and a 33% increase in electrical conductivity for Cu0.1SrZrS3. The Cu/SrZrS3 phase interfaces effectively hinder phonon transport, generating a 41% reduction in lattice thermal conductivity for Cu0.2SrZrS3. This work not only advances β-SrZrS3 as a robust multifunctional bulk material but also provides a general framework to unlock the vast sulfide-perovskite family for energy conversion devices.