[en] In a search for the physical origin of the first sharp diffraction peak (FSDP) in the concentration-concentration partial structure factor S_CC (k) of disordered network-forming materials, we perform first-principles molecular dynamics simulations of liquid GeSe₄ (l-GeSe₄) and liquid SiSe₂ (l-SiSe₂). These systems are designed to provide clues on the relationship between the appearance of an FSDP in the S_CC(k) structure factor and the degree of chemical order. Short-range chemical order is more pronounced in l-GeSe₄ and in l-SiSe₂ than in liquid GeSe₂. For the latter system, our level of theory does not reproduce the FSDP in the experimentally observed S_CC (k) structure factor. We find that a distinct FSDP shows up in the partial structure factor S_CC (k) for l-GeSe₄. In S_CC (k) for l-SiSe₂, we also find a feature at the FSDP location, although it is smaller compared to GeSe₄. Given the tight correlation existing between chemical order and ionicity, these results suggest that the ionic character of the bonds plays a crucial role in inducing concentration fluctuations at intermediate-range distances