To industrially utilize the facts that reduced titanium oxide obtained by reducing/transiting titania (TiO2) into a lower oxide and reduced zirconium oxide obtained by reducing/transiting zirconia (ZrO2) into a lower oxide both exhibit black, have infrared activity, and also have catalytic activity to the reduction reaction of carbon dioxide.

The structure in reduced titanium oxide of a single phase is changed into a polymorphic structure where two solid phases are coexist in equilibrium, so as to strengthen its infrared activity. On the other hand, different elements or different metal oxides with different valencies are added/solid-soluted into reduced titanium oxide and reduced zirconium oxide, so as to stabilize its structure, and also, the chemical composition thereof is made into a non-stoichiometric composition, so as to strengthen its interaction with infrared rays.

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