['The', 'measurements', 'were', 'carried', 'out', 'under', 'an', 'argon', 'atmosphere', '(', 'with', 'an', 'oxygen', 'content', 'of', '7', '\xa0', 'ppm', ')', ',', 'using', 'pure', 'platinum', 'ingots', '(', '64–144', '\xa0', 'mg', ')', 'of', '99.95', '\xa0', 'at', '%', 'purity', 'as', 'a', 'reference', 'material', '.']