Structural and magnetic behaviour of lead-bismuthate glasses containing rare earth ions

Lead-bismuthate glasses containing rare earth ions in the xR(2)O(3)(1 - x)[3Bi(2)O(3)center dot PbO] (R = Nd, Eu, Er and Gd), xCeO(2)(1 - x)[3Bi(2)O(3)center dot PbO] and xTb(4)O(7)(1 - x)[3Bi(2)O(3)center dot PbO] vitreous systems with x up to 0.25 were prepared and investigated by density, IR spectroscopy and magnetic susceptibility measurements. Density data show that the gradual addition of the rare earth ions leads not only to a simple incorporation of the rare earth ions in the host glass matrix but also generates structural changes of the vitreous matrix. FTIR data permitted to determine the Bi3+/Bi6+ ratio of the samples and to follow the compositional evolution of the structural changes for the studied systems. Magnetic susceptibility data show that the magnetic rare earth ions appear as isolated species for low rare earth oxide contents (x <= 0.03 divided by 0.05) and as both isolated and magnetically coupled species for higher contents. All the magnetic rare earth ions present a very accentuated clustering tendency. Some of the studied rare earth ions appear in the host glass matrix in a single valence state (neodymium, gadolinium, and erbium), namely the 3+ one. Other rare earth ions appear in two valence states (i.e., cerium, europium and terbium), but the 3+ one is the most stable. (C) 2010 Elsevier B.V. All rights reserved.