Several Th(1-x)Ln(x)O(2-x/2) mixed-oxides (Ln = Nd, Sm, Gd, Dy, Er or Yb) were prepared from oxalate precursors. Structural and microstructural investigations of both initial precursors and resulting oxides were undertaken by XRD, mu-Raman spectroscopy and SEM, with a particular attention paid to the Th1-xNdxO2-x/2 series. For oxides, XRD and mu-Raman agreed well with the stabilization of the Fm (3) over barm structure up to x(Nd) = 0.4, thanks to the concomitant creation of oxygen vacancies, as also confirmed by mu-Raman. Then, a structural transition to the Ia (3) over bar superstructure occurred. For x(Nd) >= 0.49, mixed-oxides with an additional hexagonal Nd2O3 phase were prepared. Besides, the unit cell parameter of the Th(1-x)Ln(x)O(2-x/2) series followed a quadratic relation versus the x substitution rate as a result of the combination between modifications of cationic radius and cation coordination, and the decrease of O-O repulsion linked to the presence of oxygen vacancies. (C) 2012 Elsevier Ltd. All rights reserved.