Phosphates of general formula M0.5Hf2(PO4)(3) with M = Cd2+, Ca2+, Sr2+ and Cu2+ were prepared by coprecipitation and characterized by several physical techniques. The compounds containing Cd2+, Ca2+, Sr2+ belong to the Nasicon-type structure, whereas Cu0.5Hf2(PO4)(3) exhibited substantially different DRX patterns. Combined temperature programmed reduction (TPR) and temperature-programmed oxidation (TPO) showed that the copper in Cu0.5Hf2(PO4)(3) was distributed between two energetically different sites in proportions respectively equal to 40 and 60%. Electron Paramagnetic Resonance (EPR) investigations confirmed the TPR/TPO results and revealed that the two sites hosting the Cu2+ ions are of orthorhombic symmetry. Moreover, the Cu2+ ions might be reduced by hydrogen to Cu+. These results were also supported by the W-visible studies that showed the disappearance, under reducing conditions, of the band corresponding to crystal field transitions of Cu2+ ions and the emergence of a new peak attributed to the transitions between (3d)(10) and (3d)(9)(4s)(1) Cu+ levels. At the same time, IR spectroscopy confirmed that protons entered the open lattice framework of the material and gave rise to a new protonated phase containing monovalent copper (Cu0.5H0.5Hf2)-H-I(PO4)(3). This redox process was proven to be reversible without any subsequent change in the network of the phosphate.