Page 101 - Electrical Properties of Materials

Exercises 83

where r 0 is the equilibrium distance between the atoms. mn
c =– E c .
Discuss the criterion of breaking used to get the above result. 9r 3
0
5.4. For the KCl crystal the variation of energy may also be
5.6. Calculate the energy of a negative ion in a linear chain
described by eqn (5.8), but now r means the interatomic dis-
of equally spaced ions, which carry alternative positive and
tance in the cubic crystal, and the energy is for an ion pair. negative charges.
2
Take m =1, n =9, B = 1.75e /4π 0 . The bulk modulus of
–2
10
elasticity is 1.88 × 10 Nm . Calculate the separation of the 5.7. For a symmetrical coupled system, the decrease in en-
+
–
K –Cl ions in the ionic solid. ergy (with respect to the uncoupled case) is A,asshown by
eqn (5.38). Show that, for an unsymmetrical system (H 11 =
2
5.5. Show with the aid of eqns (5.7)–(5.9) that the bulk H 22 ) with the same coupling (H 12 H 21 = A ), the decrease in
modulus may be obtained in the form energy is less than A.