Question

Gibbs free energy of an alloy (9 marks The stability of a pseudobinary alloy (see lecture week 5) is subject to the minimization of the Gibbs free energy of mixing Let us consider the pseudobinary alloy AB1-C which crystallizes as a zincblende. The solid solution can be considered as formed by the 5 possible tetrahedra with an atom C in the centre and A or B atoms at the corners A4C, A3BC, A2B2C, AiB3C B4C which can be written as A4-nB,C for n-0...4. I Part a (1 marks) Calculate the probability P,(x) of each tetrahedron for a composition x in the alloy (x A atoms and 1-x B atoms in the random approximation Part b (4 marks) For the same composition x 1) Calculate the number of microstates 2 for 1 mole of the alloy 2) Demonstrate that the entropy of mixing is: Sm-NkB(rlnz+(1 n(1- x)

Answer 1

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