Thin film ZnO-doped Ce-4.67(SiO4)(3)O (ZCS) oxy-apatite was synthesized via room temperature sputtering of binary oxide precursor components followed by low oxygen partial pressure (p(O-2) similar to 10(-20) atm) annealing at temperatures not exceeding 1100 K to enable interfacial reactions and phase formation. During the synthesis, the emergence of apatite phase is identified by in-situ electrical conductivity measurements and this is correlated with ex-situ investigations including X-ray diffraction and X-ray photoelectron spectroscopy. The synthesized ZCS apatite films show good mixed conductivity. Solid oxide fuel cells (SOFC) implementing Ni-apatite co-deposited composite electrodes are demonstrated for the first time with a peak power density of similar to 105 mW cm(-2) at 823 K which presents feasibility of thin film solid state reactions as a means of synthesis of challenging metastable phases and their explorations in energy conversion. (C) 2016 The Electrochemical Society. All rights reserved.