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Hochleitner, Rupert; Schröcke, H. (1994): Ternary compounds in the systems Mn-Ta-O and Fe-Ta-O and the formation of Ta-columbites from the gas phase [Ternare Verbindungen in den Systemen Mn-Ta-O und Fe-Ta-O und die Entstehung von Columbiten aus der Gasphase]. In: Freiberger Forschungshefte, Reihe C, No. C451: pp. 88-113
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In the system Mn-Ta-O there are two ternary oxides at 1000°C, the columbite phase MnTa2O6 and a corundum phase with the non stable formula Mn4Ta2O9, which are homogenous in the join MnO-TaO2.5 from 62 to 67 and 26 to 28.4 mol\% TaO2.5. Free enthalpy data are determined with electrochemical measurements of fO2 of quaternary coexistences of three crystalline phases and a gas phase. The formation of Ta-columbites together with wolframite, spinel and cassiterite is examined with exchange reactions. -from English summary