Abstract
Alkaline earth-copper oxide binary mixtures were reacted in elevated oxygen pressure up to 200 bar in the temperature range 880–950°C. The phases which were formed have been identified by X-ray powder diffraction analysis. The compounds which become stabilized at higher P(O 2) are Ba 2Cu 3O 5+ δ , Sr 2CuO 3+ δ , (Sr 14Cu 24) 1- x O 41 and Ca 4Cu 5O 10. These compounds have formal copper valence (FCV) in the range of 2.4 to 2.8 and are therefore favored at higher P(O 2) over the ABO 2 and A 2BO 3 compounds obtained at 1 bar which have FCV=2. The transition pressures to the more oxidized cuprates are ∼10 bar for Ca 2CuO 3/Ca 4Cu 5O 10, 17.5 bar for BaCuO 2/Ba 2Cu 3O 5+ δ and 40 bar for SrCuO 2/(Sr 14Cu 24) 1- x O 41 at 880–950°C.
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