Amorphous bismuth phosphate prepared by mechanochemical process

The mechanochemical (MC) method was applied to promote the amorphization of BiPO 4 crystals via Fe 3+ substitution (x=0.15 in Fe x Bi 1-x PO 4 ). While pure BiPO 4 exhibited limited glass-forming ability, retaining its low-temperature monoclinic phase (LTMP, M 1 phase) after 10 h of milling, the introduction of Fe 3+ significantly accelerated amorphization, achieving substantial structural refinement within just 1 h of milling. This enhancement is attributed to the unique structural characteristics of the LTMP phase (space group P2 1 /n), which features unequal lattice parameters and distorted arrangement of Bi and PO 4 units. Such distortion renders the LTMP phase more susceptible to amorphization compared to the high-temperature monoclinic phase (HTMP, space group P2 1 /m), which has more regular and stable lattice parameters. Notably, even a small substitution of Fe 3+ (x=0.05) reduced the crystallite size by over 50% to approximately 6.5-9.1 nm, demonstrating effective disruption and refinement of the LTMP structure. These findings underscore the critical role of Fe 3+ in facilitating the rapid amorphization of BiPO 4 . • Fe 3+ substitution enhanced amorphization of BiPO 4 . • Reversible polymorph transitions in BiPO 4 as heat treatment temperature. • Intermediate temperatures induce dynamic metastable states during phase transitions.