| http://www.w3.org/ns/prov#value | - Preferred active metal oxides are those metal oxides having a Group 4 metal, such as zirconium and/or hafnium, either alone or in combination with a Group 2 (for example magnesium, calcium, strontium and barium) and/or a Group 3 metal (including the Lanthanides and Actinides) oxide (for example yttrium, scandium and lanthanum).
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