Reduction of Ba sub 2 YCu sub 3 O sub 7 and Y sub 2 Cu sub 2 O sub 5 by H sub 2 .

The reduction of Ba sub 2 YCu sub 3 O sub 7 and Y sub 2 Cu sub 2 O sub 5 was studied in 15% H sub 2 - 85% N sub 2 . Although a considerable structure is evident in the thermogravimetric (TG) curves, x-ray diffraction studies of partially reduced samples did not reveal any obvious intermediates. At 980C Ba sub 2 Y sub 2 Cu sub 3 O sub 7 is reduced to BaO, Ba sub 2 Y sub O sub 5 and Cu. Near 800C there is a plateau in the TG curve corresponding to Cu sup (1+) and 2Cu. This suggests the formation of YCuO sub 2 , however, there is no x-ray evidence in the powder pattern. Similarly, YCuO sub 2 does not appear as a stoichiometric intermediate in the reduction of Y sub 2 Cu sub 2 O sub 5 by H sub 2 . X-ray diffraction shows the presence of Cu at an early stage in reduction of Ba sub 2 YCu sub 3 O sub 7 suggesting a surface reaction which is nearly completed before substantial reduction occurs in the interior of the particle.