Location of Cu2+ ions in some protoned Nasicon-type phosphates

Nasicon-type phosphates Cu1−xHxZr2(PO4)3 (0 < x <1) and Cu1−xH2x−1Zr2(PO4)3 (0.5 < x <1) have been investigated by magnetic susceptibility and electron paramagnetic resonance (EPR). Room-temperature EPR spectra at X-band (9.5 GHz) exhibit relatively different local information about paramagnetic environments in the two sets. Analysis by computer simulations of Cu1−xHxZr2(PO4)3 spectra reveals that Cu2+ ion is located in an axially distorted octahedron, which can be assigned to the M(1) site. However, in the case of Cu1−xH2x−1Zr2(PO4)3, EPR parameters suggest that Cu2+ ions are distributed in two types of sites with axial and lower than axial symmetries; these latter can be attributed to M(1) and M(2) sites respectively. g and A components are related to structural properties using molecular orbital method. Data are obtained on variations of the bond covalence with the composition.