Structural features and rare earth ion clustering behavior in lanthanum phosphate and aluminophosphate glasses from molecular dynamics simulations

This paper reports detailed short and medium range structural features of lanthanum oxide containing alkaline phosphate and aluminophosphate glasses revealed from molecular dynamics simulations. Two glass series xLa(2)O(3)-(100-x)NaPO2 (x = 0-7.5) and xLa(2)O(3)-yAl(2)O(3)-(100-x-y) NaPO3 (0 <= x <= 5 and 5 <= y <= 15) were studied and the cation local environments as a function of compositions in terms of partial distribution functions, bond angle distributions and oxygen coordination number investigated. It was found that La-O has a bond distance of similar to x223C2.44 angstrom and average coordination number 6.5-7, consistent with experimental findings based on neutron and X-ray diffractions. Medium range structure feactures such as Q(n) distribution, network connectivity and polyhedral linkages were studied. The clustering behavior of lanthanum ions in the glasses were investigated in detail and it was found that La3+ ions are mainly surrounded by PO4 units in the second coordination shell that prevented La3+ ion from clustering. As a result, the addition of alumina does not significantly change the clustering behavior.