Solid solutions of iron oxide in MgO, prepared using the solid state reaction method (SSR), were investigated for solar thermochemical water splitting/carbon dioxide splitting (STC-WS/CDS). Experimental results show that 20 mole% magnetite (Fe3O4) in MgO has a hydrogen (H-2) production capacity of 6.12 +/- 0.22 cm(3) g(total material)(-1) when thermally reduced at 1450 degrees C (T-red) under an inert environment and oxidized at 1200 degrees C (T-ox) with excess steam. This compares favorably with cerium dioxide (CeO2), which has proven to be an excellent STC-WS/CDS material, with H-2 production 2.91 +/- 0.15 cm(3) g(total material)(-1) at T-red = 1450 degrees C and T-ox = 1200 degrees C, and 4.34 +/- 0.2 cm(3) g(total material)(-1) at T-red = 1500 degrees C and T-ox = 1200 degrees C. 20 mole% Fe3O4 in MgO has advantages of lower operating temperature and higher production capacity. The partial pressure of oxygen (P-o2) during thermal reduction is on the order of 10(-4) atm, which can be achieved using existing industrial vacuum pump technology. These advantages make this material a viable option for further study in solar thermochemical fuel production applications.