Structural, thermal behavior, dielectric and vibrational studies of the new compound, sodium hydrogen arsenate tellurate (Na2H4As2O5.H2TeO4) Review Article

The structure of Na2H4As2O5.H2TeO4 (NaAsTe) crystallizes in the tetragonal system I4̄. The unit cell parameters are a =b =5.576(2) ˚, c =7.773(5) ˚, Z =2, and V =241.8(2) ˚3. The main feature of the crystal structure is the coexistence of two independent and different anions, As2View the MathML sourceO54− and TeView the MathML sourceO44−, in the unit cell, connected by strong (O–H…O) hydrogen bonds, which make the packing of the crystal. The polyhedra in the structure arranged allows formation of tunnels where hydrogen atoms are placed. The structural cohesion for this material is assured both by the interaction between Na+ and the anionic oxygen atoms and by the presence of strong hydrogen bonds. The NaAsTe material undergoes three endothermic peaks at 417, 421, and 450 K. These transitions, detected by differential scanning calorimetry (DSC) and confirmed by Thermogravimetry, differential thermal analysis (DTA–TG) analyses, are also substantiated by dielectric and conductivity measurements using the impedance spectroscopy techniques. In fact, the peak at 417 K is attributed to ferroelectric–paraelectric phase transition while the second one, at 421 K, is assigned to ionic–protonic conduction. The third anomaly at 450 K can be attributed to the decomposition of the material confirmed by TG analysis. The infrared (IR) and Raman spectra recorded at room temperatures, in the frequency ranges 4000–400 cm−1 and 200–1500 cm−1, respectively, bear out the presence of anionic groups in the crystal and the presence of strong hydrogen bonds.