LONDON (Reuters) -The U.S. Defense Logistics Agency is seeking to buy scandium oxide worth up to $40 million over the next five years from a unit of mining giant Rio Tinto to secure supplies of the critical material for addition to the national stockpile. Scandium is one of the rare earth elements, whose importance to the Western defence and technology sectors has been in the spotlight since China, the main producer, imposed export controls. "Scandium, until recently, was primarily sourced from China. In ...