  This work concerns glasses belonging to SiO2-Al2O3-CaO-ZrO2-TiO2-Nd2O3 system
that lead to zirconolite crystallization in their bulk after nucleation +
crystal growth thermal treatments and that could find application as nuclear
waste form. The understanding of crystallization processes in glasses implied
to investigate their structure. The environment around Ti, Zr (nucleating
agents) and Nd was characterized for various Nd2O3 loadings. Electron spin
resonance study of the small amount of Ti3+ occurring in glasses enabled to
identify two types of sites for titanium. EXAFS showed that Zr occupied a quite
well defined 6-7-fold site coordinated by oxygen at 2.20 {\AA}, with second
neighbors that could correspond to Ca/Ti and Zr around 3.5 {\AA}. This short
range order presents some similarities with zirconolite, which could predispose
glass to zirconolite nucleation. Nd environment was probed by optical
spectroscopies, ESR and EXAFS. Results showed that the environment around Nd
was very constrained by the glassy network and significantly differed from the
one in zirconolite. Nd occupied a highly distorted 8-9-fold coordinated site in
glass with oxygen atoms at 2.53 {\AA}. No second neighbors were clearly
identified by EXAFS around Nd, but the study of Nd optical fluorescence decays
suggested a strong interaction between Nd ions.
