The Ca0.5-xMgxTi2(PO4)(3) series (0.0 <= x <= 0.5) was prepared by a sol-gel method. X-ray diffraction patterns showed two rhombohedral phases which coexist for intermediate compositions. Despite of the absence of a solid solution mechanism for the whole stoichiometry range, an appreciable cation mixing was observed in both phases. P-31 MAS NMR spectroscopy revealed that low magnesium contents are incorporated to the calcium compound inducing changes in the ordering of the alkaline earth cations in MI sites. Derivative plots of the voltage-capacity curves revealed two reversible regions ascribed to the reduction of Ti4+ to Ti3+, ascribable to the subsequent insertion of lithium ions into M-1 and M-2 vacant sites. Capacity values as high as 138 mAh/g after the first discharge were monitored for nanometric Ca0.15Mg0.35Ti2(PO4)(3) at C/20. Cell cycling under successive kinetic rates revealed a good capacity retention for samples with x = 0.15 and 0.25. Impedance spectra were recorded in lithium cells discharged after different number of cycles at different Crates. The increase in charge transfer resistance was shown to be an important factor determining the electrode behavior on extended cycling. (C) 2013 Elsevier Ltd. All rights reserved.