The reactive ceramics suitable for the rotary-type solar reactor (proposed by Tokyo Institute of Technology, Tokyo) with two-step water-splitting reaction were developed. It is confirmed that O(2) gas is evolved in the two-step water-splitting reaction with the reactive ceramics vigorously by rapid heating (alpha-O(2)-releasing reaction). The alpha-O(2)-releasing reaction is due to the formation of interstitial defect and the conversion of lattice oxygen into O(2) gas at a nonequilibrium state. Reactive ceramics (NiFe(2)O(4) and yttria stabilized zirconia (YSZ)-NiFe(2)O(4) solid solution) can absorb solar thermal energy and convert thermal energy into chemical energy under high O(2) partial pressure atmosphere in the alpha-O(2)-releasing reaction. Repetitive evolutions of O(2) gas were observed in the two-step water-splitting reaction with YSZ-Fe(3)O(4) solid solution and cerium based metal oxides (CeO(2)-NiO, CeO(2)-ZrO(2), and CeO(2)-Ta(2)O(5)) at high O(2) partial pressure. The CeO(2)-Ta(2)O(5) (Ce: Ta = 90: 10) released a large amount of O(2) gas (3.95 cm(3)/g) in the alpha-O(2) releasing reaction in the flow of air. [DOI: 10.1115/1.4001180]