الفهرس 
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Abstract
This study was focused on the theoretical study of
BayK(1_y)Bi(1-x)Pbx03 using molecular dynamics (MD)
simulation. The structure of (Bi203)6o(K20)4o_y(BaO)y,
(PbO)6o(K20)4o_y(BaO)y, (Bi203)3o(PbO)3o(K20)4o_y(BaO)y (0 :S
y :S 40), and (Bi203)6o-x(PbO)xCK20)2o(BaO)2o (10:S x:S 50)
was studied using pair distribution function (PDF).
The following conclusions can be drawn from this
study:
1. The simulated glasses oxide of BayK(1_y)Bi(l_x)Pbx03 can be
classified under a ferroelectric material due to:
I. The simulated glasses confirmed the chemical
formula of the perovskite AB03-o.
11. The bond distance of Pb-O was found to be 2.4A.
111. Bi06 was found in the glass structure.
IV. The computed phonon energy E of the simulated
glasses was found to be just under the scale of the
ferroelectric material of Ba’TrOj.
2. The pair distribution function (PDF) is a very important
tool in studying the structure of glasses in the absence of long
range order.
3. In the case of substitution of K20 with BaO, the following
notices can be observed :
I. The values of computed 9Ba-nbo(r) increased while
9K-nbO(r) decreased.
11. The values of the computed 9Bi06(r) and gBi-Bi(r) were
almost fixed.
Ill. The values of the computed 9Pb-o(r) and 9Pb-Pb(r)
were slightly changed.
IV. In the presence of two formers (Bi203 and PbO) the
variation of the computed 9Bi06(r) and 9Bi-Bi(r) was
significant. Additionally the variation of the gpb-O(r)
and 9Pb-Pb(r) was less when using only one former
(PbO or Bi203).
4. In the case of substitution ofBi203 with PbO, a significant
variation was seen only in the values of the computed g(r) as
well as in the peaks position.
5. The peaks position of the computed 9Bi-Bi(r) and 9Pb-Pb(r)
were not changed during replacement of K20 with BaO and of
Bi203 with PbO (r = 3.7ft..) which means that the formers (Bi3+
and Pb2+) have fixed positions in the glass structure.
6. The computed coordination number ne approximately
unchanged by substituting K20 with BaO while significant
variations were observed by replacing Bh03 with PbO.
7. The computed density p of the simulated glasses increased
by substituting K20 with BaO.
8. The computed density p of the simulated glasses increased
up to 20 mol%, then decreased gradually to reach 6.11 g/cm ’
at x = 50 mol% in case of replacement Bi203 with PbO.
9. The elastic properties computations are useful tool to test
the computer modeling approaches through the relation
between the structure and elastic properties.
10. In case of replacement ofa former (Bi203 and PbO) with
a modifier (K20 and BaO), the values of the computed elastic
moduli, Young’s Y and bulk B, and Debye temperature BD
increased, which means an increment in rigidity of the glasses.
11. The Bi203 as a former has a higher effect on the
improvement of the elastic properties of the simulated glasses
in comparison to PbO.