Post-ball-milling-assisted solid-state synthesis of Bi4O4SeCl2: A low thermal conductivity material

Abstract

This study investigates the synthesis of Bi₄O₄SeCl₂ through a cost-effective ball-milling-assisted solid-state reaction method. The as-grown samples predominantly consisted of the Bi₁₂O₁₅Cl₆ phase, with minor contributions from BiOCl and Bi₄O₄SeCl₂. A systematic post-ball-milling process was applied to enhance the formation of the Bi₄O₄SeCl₂ phase. Prolonged milling time led to the progressive dominance of the Bi₄O₄SeCl₂ phase, resulting in significant improvements in electrical conductivity and reductions in thermal conductivity. After 30 min of milling, the carrier concentration increased notably from −2.23 × 10¹⁶ cm⁻³ (as-grown) to −1.01 × 10¹⁸ cm⁻³, while electrical conductivity rose from 0.14 S/cm (as-grown) to 2.26 S/cm. Simultaneously, thermal conductivity decreased from 0.65 W m⁻¹ K⁻¹ (as-grown) to 0.35 W m⁻¹ K⁻¹. These findings demonstrate that post-ball-milling is a scalable and economical method for synthesizing Bi₄O₄SeCl₂ with low thermal conductivity, highlighting its potential as a promising material for thermal barrier coatings and thermoelectric applications.