(Y1-xNdx)(3)Zr5O14.5 solid solutions as inert matrices: Phase evolution, order-disorder dynamics and thermophysical behavior

In order to understand structural implications of higher loading of minor actinides (MA) in zirconia-based materials for transmutation, substitution of Nd3+ in Y3Zr5O14.5 has been explored. Nd3+ is surrogate for minor actinides (Am3+, Cm3+). Various compositions in (Y1-xNdx)(3)Zr5O14.5 (0 <= x <= 1.0) system have been synthesized by high temperature route. The X-ray diffraction studies established end members Y3Zr5O14.5 and Nd3Zr5O14.5 as defect fluorite (F) and non-stoichiometric pymchlore-type (P), respectively. The defect fluorite persisted till 60 mol% Nd3+ -substitution followed by biphasic phase field in F and P- type phases. Interestingly, the Raman spectra revealed the onset of localized pymchlore-type superstructure much earlier (after 40 mol% Nd3+). Thermal diffusivity of representative nominal compositions were obtained by Laser Flash Technique. Nd3+ substitution lowered the thermal conductivity of stabilized zirconia due to additional scattering centres introduced. The work highlights implications of hidden ordered structural features on thermal conductivity trends, which has significance for increasing MA loading.