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Terbium(III,IV) oxide, occasionally called tetraterbium heptaoxide, has the formula Tb4O7. There is some debate as to whether it is a discrete compound, or simply one phase in an interstitial oxide system.
T 1260 (OTTO) Terbium oxide, GR 99.99% Cas 12037-01-3 - used in fluorescent lamps and color picture tubes.