AbstractKnowledge about the nucleation, growth, and formation mechanisms during materials synthesis using sol-gel and solution-based methods is important to design a material with desired properties. We used aqueous chemical synthesis as an environmentally friendly and highly flexible route to tailored and reproducible synthesis of oxide nanomaterials and thin films. For studies of hydrothermal synthesis an in situ cell using synchrotron X-ray diffraction was used to investigate the formation mechanisms of Sr_xBa_1-xNb₂O₆ piezoelectrics. Aqueous chemical solution deposition of phase pure oriented piezoelectric thin films demands strong control of processing parameters. An in situ cell for synchrotron X-ray diffraction studies of the annealing and crystallisation steps during aqueous chemical solution deposition was used to understand the nucleation and crystallisation of Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT). We discuss how the knowledge about nucleation and growth obtained by in situ characterisation can be used to design the optimal procedure for fabrication of oxide materials with desired properties.