  Gd0.2Ce0.8O1.9/Y0.16Zr0.84O1.92 (GDC/YSZ) nanocomposite is synthesized by a
novel hybrid chemical route, where colloidal crystalline GDC nanoparticles from
continuous hydrothermal synthesis are dispersed into a metalorganic YSZ matrix
precursor. The result is a mixture of metal oxides in which GDC nanoparticles
are finely distributed in a continuous metalorganic polymeric matrix to be
crystallized after calcination. The GDC nanoparticles reduce the temperature
necessary to obtain crystalline YSZ, which is already formed at 400 {\deg}C.
The nanocomposite reveals structural stability up to 800 {\deg}C when treated
in both air and reducing atmosphere, showing the onset of diffusion below 1000
{\deg}C. The diffusional processes are largely dependent on the nanometric
grain size, with Zr4+ diffusing abruptly towards GDC in air at 1000 {\deg}C and
GDC/YSZ interdiffusion being hindered in reducing environment despite the onset
temperature of 900 {\deg}C. The nanocomposite precursor is an inkjet-printable
reactive water-based material, suitable for the deposition of thin films with a
thickness below 100 nm after calcination at 750 {\deg}C. The crystal structure
of the film reveals no interaction between GDC and YSZ but a microstrain (0.3%
tensile strain for YSZ). The thin film microstructure shows a compact layer
with 94% density. The nanocomposite shows high oxygen ionic conductivity at low
temperatures (> 5 * 10-3 S cm-1 at 500 {\deg}C), low activation energy (0.55
eV), and dominant oxygen ionic conductivity even in reducing conditions (pO2 <
10-25 atm). We show that these properties arise from the large interface
between the components of the composite, due to the embedding of the GDC
nanoparticles in the YSZ matrix, while ZrO-CeO intermixing can be avoided and
no n-type conductivity is observed even at low oxygen activities and high
temperatures.
