A systematic examination of LiTi2(PO4)(3) and Li0.9Ti1.9Nb0.1(PO4)(3) phosphates with Nasicon structure was carried out in order to investigate "order-disorder" phase transitions. The structural features of aliovalent doped Li0.9Ti1.9Nb0.1(PO4)(3) are considered in comparison with initial LiTi2(PO4)(3). Explanations of the thermal behavior of samples are proposed based on NMR Li-7, Nb-93 data, X-ray powder diffraction. DSC and impedance spectroscopy. (C) 2012 Elsevier B.V. All rights reserved.