The evolution from a partially oriented granular microstructure to a dense epitaxial one in CeO2 buffer layers deposited by metallorganic decomposition (MOD) on single crystal Y-stabilised ZrO2 (YSZ) substrates, has been investigated. CeO2 buffer layers were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), reflection high energy electron diffraction (RHEED), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Reducing atmospheric conditions inhibit grain growth resulting in a nanometric granular microstructure with a high concentration of C impurities decorating grain boundaries and porosity. Oxidation and elimination of C species promotes grain growth resulting in a dense epitaxial film, as well as stabilizes otherwise energetically prohibitive polar (001) planes. Trifluoracetate (TFA) derived MOD YBa2Cu3O7 (YBCO) films deposited on optimized CeO2 buffers exhibit a sharp interface while the undesired reaction giving BaCeO3 is minimized. Jc values of 1.5 MA/cm2 and 14 MA/cm2 at 77K and 5K, respectively, are achieved.