Tracing the origin of the first sharp diffraction peak (FSDP) of sodium metaphosphate glass and melt

The phenomenon of `first sharp diffraction peaksʹ (FSDP) present in the diffractograms of certain amorphous solid or liquid systems below the so-called main diffraction peak is studied by the use of Fourier transforms remaining within the diffraction theory of non-crystalline systems. Performing the inverse transformation of the reduced radial distribution functions (RDFs) in separate parts enables us to trace the origin of an FSDP – or any other features of the diffraction pattern – to real space. This means that all pieces of information on the (disordered) structure contained by the structure factors are comprised of the pair distribution functions too. The input of extraneous distances, layers, etc. is unnecessary and therefore misleading.