Solubility of ThO 2 in Gd 2Zr 2O 7 pyrochlore: XRD, SEM and Raman spectroscopic studies

Abstract

Solubility of ThO 2 in gadolinium zirconate pyrochlore, a potential host for radioactive materials, has been investigated. The phase relations in Gd 2− x Th x Zr 2O 7+ x /2 (0.0 ⩽ x ⩽ 2.0) systems have been established under the slow-cooled conditions from 1400 °C. XRD studies reveal that the compositions corresponding to x = 0.0–0.075 are single phasic in nature and beyond x ⩾ 0.1 the biphasic region starts. The first biphasic region comprising of pyrochlore and thoria exist from x = 0.1–0.8, and from x = 1.2 another biphasic region consisting of gadolinia stabilized zirconia (GSZ) and thoria appears which persists till x = 1.6. The end member (i.e. x = 2.0) of the series is found to be a mixture of monoclinic ZrO 2 and thoria. Interestingly, gadolinia which has wide solubility in thoria, did not show any miscibility in thoria in the presence of zirconia. Irregular grains of Gd 1.8Th 0.2Zr 2O 7.1 as shown in SEM supports its biphasic nature. Raman spectra of heavily thoria doped ( x = 0.1 and 0.2) samples, indicates the presence of Zr–O 7 mode which implies the samples are highly disordered in nature.