The pseudoternary system BaO-ZrO_2-MoO_x (where x = 0, 2, 3) wasstudied in reducing and oxidizing conditions in the temperature range1200℃-1600℃ In oxidizing conditions (pO_2 >10~(-4) atm), BaO reactspreferably with MoO_3 giving Mo~(6+) compounds such as BaMoO_4,Ba_2MoO_5 and Ba_3MoO_6 in equilibrium with ZrO_2, BaZrO_3,Ba_3Zr_2O_7 and Ba_2ZrO_4 as a function of the composition. Inreducing conditions (pO_2<10~(-20)atm), Mo~0 is formed so that BaOreacts preferably with ZrO_2 giving the perovskite Ba(Zr_(1-x)Mo_x)O_3 which can be in equilibrium with the Mo~(4+) compoundBa(Mo_(1-y)Zr_y)O_3 at 1200℃ and with the Mo~(6+) compound Ba_3MoO_6at higher temperature so that Mo~0, Mo~_(4+) and Mo~(6+) compoundscan coexist in equilibrium.
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