A black material A was prepared by heating 0.3978 g of CuO, 0.1480 g of BaCO₃, and 1.5069 g of La₂O₃ to 700 °C under N₂ and rapidly cooling to room temperature. A contains 15.79% O by mass and exhibited no weight loss on heating under a flow of He. A second black material B was prepared by heating La₂CuO₄ to 1070 °C for 17 hours in air and then slowly cooled under flow of O₂. When 20 mg of B was heated to 380 °C under flow of Ar, it lost 0.059 mg. Calculate the chemical formulae of A and B, and indicate how their electronic properties might be expected to differ from those of pure La₂CuO₄.