Discovery of Structurally Diverse Zintl Polyphosphides (Eu,Sr)P x by Computationally Assisted High-Pressure Synthesis

Phosphorus exhibits rich allotropy that gives rise to diverse polyanionic clusters and networks. The unusual transport phenomena observed in black phosphorus and its magnetic analogue α-EuP3 highlight the potential of extended phosphorus networks to generate emergent electronic properties. At the same time, high pressure has a natural affinity with P-rich polyphosphides, as it offers access to structurally diverse phosphorus networks, presenting them as a promising platform for materials discovery. In this work, P-rich compounds in the Sr−P and Eu−P systems were explored by combining high-pressure synthesis with first-principles calculations. Five previously unknown polyphosphides were synthesized across the P-rich composition range AP8−AP10 (A = Eu, Sr): EuP8, EuP9, EuP10, SrP8, and SrP10. These compounds contain chain-like and cage-like phosphorus frameworks, with varying lone-pair-bearing P concentrations across compositions. Pressure-dependent convex-hull calculations incorporating the experimentally determined structures identify a narrow moderate pressure window of 2−4 GPa in which the discovered P-rich phases become synthetically accessible, thereby providing a practical guide to their high-pressure synthesis conditions. These results demonstrate that computationally assisted high-pressure synthesis provides a powerful approach to discovering unexplored metastable phases and developing magnetic and topological functionalities in anion-rich binary Zintl compounds.