Abstract: There are provided a film of surface Nb-containing La-STO cubic crystal particles that is effective as, for example, a thermoelectric conversion material for use at low temperatures of around room temperature, and an art for producing this film. The production method includes preparing a mixed aqueous solution in which an La-containing compound, an Sr-containing compound, a six-fold coordinated Ti complex compound, and an amphiphilic compound are dissolved; growing cubic-form crystals formed of La-doped STO in the mixed aqueous solution by a hydrothermal synthesis method; obtaining surface Nb-containing La-STO cubic crystal particles by dissolving a niobium-containing compound in this mixed solution and heating; and forming a particle film in which the surface Nb-containing La-STO cubic crystal particles are bonded, by disposing the surface Nb-containing La-STO cubic crystal particles on a substrate and carrying out firing.