Question

Antifluorite structure (A2B) occurs when anions occupy lattice positions and cations occupy eight tetrahedral lattice sites of f. c. c. One of the best examples which has this structure is Li2O. The ionic radii of Li+ and O2- are as follows : rLi+ = 0.068 nm and rO2- = 0.140 nm. (20 points) a) Draw the antifluorite unit cell of Li2O and show the Li+ and O2- ions in the unit cell. State the equivalent positions of Li+ and O2- ions in the unit cell. How many net ions of each are there in the Li2O unit cell? Why? Provide explanations. How many formula units are there per this unit cell? b) Determine the number of nearest neighbors or the coordination number (C. N.) of each ion in the Li2O unit cell. Provide explanations, if necessary. c) Calculate the ionic packing factor (IPF) of the Lii2O unit cell. d) What are the closed-packed planes in the Li2O unit cell? Express their Miller indices. On this basis, determine the stacking sequence of the Li2O unit cell. (Hint : Use A, B, C for one kind of ion and use , ,  for the other kind)

Answer 1