Structural behavior, crystal chemistry, and phase transitions in substituted leucite; high-resolution neutron powder diffraction studies

Determination of Transmutation Effects in Crystalline Waste Forms

“…However, structural disorder may be a factor. While the fractional coordinates are nearly identical to those observed by Palmer et al [4], the thermal parameters are significantly larger, suggesting greater disorder in our sample. Large thermal parameters have been observed in other pollucite samples [4,12,13].…”

“…While the fractional coordinates are nearly identical to those observed by Palmer et al [4], the thermal parameters are significantly larger, suggesting greater disorder in our sample. Large thermal parameters have been observed in other pollucite samples [4,12,13]. Structural disorder leading to lattice expansion could be due to synthesis conditions, transmutation effects [14], or radiation-induced defects, such as vacancies, interstitials, and trapped electronic excitations that also lead to structural distortions.…”

“…These lattice parameters are approximately 1.0 and 0.4% larger, respectively, than the lattice parameters determined by Palmer et al as interpolated to 50 K [4]. Typically, a larger-than-expected lattice parameter can be explained by the substitution of cations with larger ionic radius into the lattice or by structural disorder.…”

“…At temperatures below 100ºC, pollucite undergoes a reversible displacive phase transition to a tetragonal phase, which has spacegroup I4 1 /a. The c/a ratio of the tetragonal phase is only 1.0051, and so it was not recognized as a distinct phase until recently [4]. The crystal structure of cubic pollucite is illustrated in Figure 1.…”

Espectros de emisión de radioluminiscencia y termoluminiscencia de una leucita de Monte Somma (Italia)

“…La red cristalográfica tetragonal de la leucita (I4 1 /a) a temperatura ambiente, se transforma en cúbica (Ia3d) cuando se calienta por encima de los 600 o C, aunque tiene un comportamiento reversible y en el enfriamiento hasta temperatura ambiente retorna a su red tetragonal (I4 1 /a). La estructura cristalina de la leucita ( (8).…”