| http://www.w3.org/ns/prov#value | - one Group IIIa element other than cerium: provided that a total of at least 5% are atoms of at least one variable valency element selected from titanium, cerium, praseodymium, and terbium; and the elements present include titanium and at least one Group IIIa element, or at least two Group IIIa elements; and the total amount of any cerium and any non-variable valency Group IIIa atoms is at least 5
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