Thermodynamik und Struktur von Ni1−xTe*

摘要

The thermodynamic properties and structural properties of Ni1−xTe have been studied using galvanic cell and X-ray diffraction techniques. The Ni1−xTe phase extends from NiTe (x=0) which has a NiAs type structure to Ni0.5Te (x=0.5) which has the CdI2structure. The phase field between the two compounds is continuous and a second order type transition is taking place aroundx=0.25. At that composition the Ni-activity vs. composition curve changes slope. Thecolattice parameter also changes drastically and diffraction lines due to the ordered CdI2structure start to appear. The intensity of diffraction lines varies smoothly from the NiAs structure to the CdI2structure. The intensities agree with that calculated for NiAs whenx0.4. From the activity measurement, the defect interaction energy was calculated. In the NiAs type structure, the vacancyvacancy interaction energy is zero, the vacancies do not repel or attract each other and thus are random. In the CdI2structure region the vacancy-vacancy interaction energy is positiveE11=26.5 kcal/mole. The vacancies repel each other and asc0/2 is smaller thana0the vacancies tend to avoid adjacent layers and thus form the CdI2struct