Spontaneous formation of a periodically striped structure in a gel-incorporated KDP single crystal

Typically, single crystals grown from hydrogels uniformly incorporate the gel-networks inside. However, in this study, we discovered a periodically striped microstructure in potassium dihydrogen phosphate (KDP) single crystals cultivated from silica hydrogels. This was the result of spontaneously non-uniform gel-incorporation, as demonstrated by time-of-flight secondary ion mass spectrometry. Furthermore, despite the non-uniformly distributed gel networks inside the crystal, its single-crystallinity remained intact, as verified by X-ray diffraction. Our hypothesis for the incorporation mechanism is that partial gel incorporation at certain rates of crystal growth periodically changes the local gel strength surrounding the growing crystal, leading to spontaneous alternations in the concentration of incorporated gel-networks.