High-temperature structural, thermal, and magnetic properties of the van der Waals semiconductor FePS3

Quasi-two-dimensional (2D) semiconductors based on metal thio(seleno)phosphates exhibit unique van der Waals layered structures and tunable physical properties, positioning them as promising candidates for advanced optoelectronic and spintronic applications. Among these materials, FePS3 has attracted significant attention for its antiferromagnetic ordering and excellent energy performance. However, the high-temperature structural evolution and intrinsic thermal and magnetic behaviors of FePS3, particularly in the absence of impurities, remain poorly understood. Herein, we examine the structural, thermal, and magnetic properties of FePS3 across a wide temperature range. High-temperature x-ray diffraction confirms that FePS3 maintains its layered structure up to 650 K without phase transitions, accompanied by pronounced anisotropic thermal expansion [aa = 10.6(3) μK−1, ab = 10.0(5) μK−1, αc = 15.7(7) μK−1] with a linear response to temperature. By reducing pyrrhotite impurities through 15% phosphorus excess, we eliminate extrinsic magnetic artifacts in polycrystalline samples, thereby isolating the intrinsic high-temperature thermal conductivity of FePS3. The average thermal conductivity is 2.58 W m−1 K−1 at 303 K, and 1.44 W m−1 K−1 at 723 K, with an anisotropy factor k⊥/k∥ in the range of 1.63–1.75. Notably, high-temperature magnetic measurements on single crystals reveal an S-shaped anomaly between 600 and 800 K in the inverse susceptibility, likely caused by emergent magnetic fluctuations or crystal-field effects. These findings advance the understanding of quasi-2D magnetic materials under thermal stress and provide a foundation for designing reliable functional materials for high-temperature applications.