Structural, thermal and dielectric studies in Na2SeO4.Te(OH)6.H2O

Crystal structure of Na2SeO4.Te(OH)6.H2O crystallizes in the monoclinic P21/c space group. It was analyzed at room temperature using X-ray diffractometer data. The unit cell parameters are a = 6.211(3) A, b 12.002(3) A, c = 10.210(4) A, β = 104.99(2)o, Z = 4, V = 735.19(5) A3 and ρ cal = 2.907 g cm-3. The main feature of this atomic arrangements is the coexistence of two independent and different anions (TeO66- and SeO42- groups) in the unit cell, connected by hydrogen bonds which make the building of the crystal. The thermal analysis of the title compound show three distinct endothermal peaks at 390, 420 and 430 K. The evolution of the dielectric constant as a function of frequency and temperature revealed one anomaly at about 420 K attributed to a ferro-paraelectric phase transition. However, the conductivity evolution versus temperature showed the presence of the ionic-protonic conduction phase transition at 430 K