The incorporation of plutonium (Pu) within lanthanum zirconate pyrochlore was investigated using air, argon, and N-2-3.52 sintering atmospheres together with Ca2+ and Sr2+ incorporation for charge compensation. The samples have been characterised in the first instance by X-ray diffraction (XRD), scanning electron microscopy (SEM) and diffuse reflectance spectroscopy (DRS). The results show Pu can be exchanged for La3+ on the A-site with and without charge compensation and for Zr4+ on the B-site. DRS measurements were made over the wavenumber range of 4000-19,000 cm(-1) and the Pu in all air- and argon-sintered samples was found to be present as Pu4+ while that in samples sintered in N-2-3.52 was present as Pu3+. The Pu valence was confirmed for three of the samples using X-ray near-edge absorption spectroscopy (XANES). Pu valences >4+ were not observed in any of the samples. (C) 2013 Elsevier B.V. All rights reserved.