The unit cell of the CaF2 crystal structure is shown in the Figure. [VISUAL] The addition of a small — Physical Chemistry — Thermodynamics Chemistry Question
Solid state structure
The unit cell of the CaF2 crystal structure is shown in the Figure. [VISUAL] The addition of a small amount of Y2O3 to CeO2 with the CaF2 crystal structure and heating give a solid solution Ce1-xYxO2-y, in which Ce4+ and Y3+ are homogeneously distributed at the cation sites and oxygen vacancies are formed at the anion sites. Here, the valence of the cerium ions is assumed to be constant at +4.
Indicate how many cations and anions are present in the CaF2 structure unit cell?
Model Answer
Cations: 4 Anions: 8
What is the ratio (%) of oxygen vacancies to the anion sites in the solid solution synthesized with the molar ratio of CeO2 : Y2O3 = 0.8 : 0.1.?
Model Answer
0.8(CeO2) + 0.1(Y2O3) = Ce0.8Y0.2O1.9
0.1 / 2.0 = 0.05 5 %
Calculate the number of oxygen vacancies contained in 1.00 cm3 of the above solid solution. Here, the unit cell volume a3 is 1.36 x 10–22 cm3.
Model Answer
1 / (1.36×10–22) × 8 × 0.05 = 2.94×1021