Structural single Crystal, Na-23 and P-31 MAS NMR and conductivity studies of Na2HPO4NaH2PO4Te(OH)(6)

Single crystal X-ray diffractometry of the sodium phosphate tellurate compound Na2HPO4NaH2PO4Te(OH)(6) (NaPTe) shows that the compound crystallizes in a trigonal system with a P3 space group. The unit cell parameters were as follows: a = 7.861(1) angstrom and c = 10.8326(1) angstrom, V = 579.7(2) angstrom(3) and Z = 2. The asymmetric unit is made up of two unequivalent Te(OH)(6) groups, four unequivalent PO4 groups and two unequivalent Na+ cations. Material cohesion is built of O-H...O bondings and ionic interactions. Magic angle spinning nuclear magnetic resonance (MAS NMR) P-31 and Na-23 analysis were used to confirm the crystal structure investigation. Indeed, the observed values of Na-23 NMR chemical shift are found to be -4.58 and 3.35 ppm revealing the presence of two non-equivalent sodium nuclei in the structure. Moreover, the simulation of the P-31 NMR spectrum exhibits four sites with a similar abundance observed at 1.6, 3.8, 3.2 and 2.8 ppm chemical shifts. AC complex impedance measurements performed on the NaPTe compound showed a significant level of conductivity at high temperatures, probably attributable to the motion of Na+ ions and H+ protons. The conduction process in the AC conductivity is explained by the large overlapping polaron model up to 100 degrees C.