X-ray investigation of the systems BaO?WO3, BaO?MoO3 and BaO?Ta2O5

Abstract

1. Specimens of the system BaO−WO3, heated in air at 1200o, contained the following barium tungstates: BaO·WO3, 2BaO·WO3 and 3BaO·WO3. At BaCO3: WO3=1:2 ratio in the same system a mixture of the composition BaO·WO3+WO3 is formed; this mixture melts at about 940o with formation of a compound of the probable formula BaO·2WO3. 2. The main reaction product in the system BaO−WO3 is the tungstate BaO·WO3. formation of which is complete after the appropriate mixture of the original components has been heated for 2 hr at 850o. All the tungstates are stable in air for a considerable time. 3. When specimens in the system BaO−MoO3 are heated in air. three compounds are likewise formed by the solid-state reaction: BaO·MoO3. 2BaO·MoO3 and 3BaO·MoO3; however, only the molybdate.BaO·MoO3 was obtained as a single phase, event at 1200o. The molybdate 2BaO·MoO3 was obtained as the single phase when a mixture of BaO·MoO3+BaCO3 was heated in air at 1200o. 4. The main compound in the system BaO−MoO3 is the molybdate BaO·MoO3. The structures of the barium molybdates BaO·MoO3, 2BaO·MoO3, 3BaO·MoO3 are quite similar to the structures of the corresponding tungstates. 5. When specimens of the BaO−Ta2O5 system are heated in hydrogen, five barium tantalates are formed to which the following formulas may be ascribed: 5BaO·Ta2O5, 4BaO·Ta2O5, 7BaO·3Ta2O5, BaO·Ta2O5 and 3BaO·7Ta2O5. The compounds to which the formulas 7BaO·3Ta2O5 and 3BaO·7Ta2O5 are ascribed may in fact be the compounds 2.5 BaO·Ta2O5 and BaO·2.5 Ta2O5; the mixtures corresponding to the latter compostions had not been investigated.