The heat of reaction and equilibrium pressure for the oxidation reaction TbO1.5+x + ( 3 28 - x 2) O2 → ( 1 7)Tb7O12 have been measured by means of a Tian-Calvet-type calorimeter and a thermal balance. The results of the weight measurement show a reproducible hysteresis loop. The heat of reaction has been measured along the oxidation branch of the hysteresis loop. The partial molar enthalpy indicates four distinct compositional regions. First, the TbO1.5+x region which can be described in terms of a point defect model and strong interaction between neighboring excess oxygen atoms. Second, the region between TbO1.54 and TbO1.61 is interpreted as the intrinsic hysteresis region and discussed in terms of the regular solution model. Third, the region between TbO1.61 and TbO1.70 is recognized as a pseudophase region. Fourth, a region of ι phase exists in which the partial thermodynamic quantities can be compared with those of CeO1.714, PrO1.714, and TbO1.714. The partial molar enthalpy was also measured for a scanning loop which is also interpreted in terms of the four regimes.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry