Synthesis, X-ray diffraction, thermal behavior and physicochemical studies of phase transitions before the decomposition in the new phosphate tellurate protonic conductor compound

Abstract

A new mixed compound, sodium rubidium phosphate tellurate, was elaborated using the slow evaporation method at room temperature, confirmed by X-ray single-crystal diffraction. The single-crystal X-ray diffraction structure of Na_2.64Rb_0.36PO₄.Te(OH)₆ is identified for the first time. At 298 K, structural analysis indicates that this compound crystallizes in the monoclinic system with P6₃ space group. The main feature of these atomic arrangements lies in the coexistence of two different anions (PO$_{4}^{3 - }$ and TeO$_{6}^{6 - }$ groups) in the unit cell, connected by hydrogen bonds which build up the crystal. The O–H…O hydrogen bonds between Te(OH)₆ octahedrons and PO₄ tetrahedral contribute to the cohesion and the stability of the atomic arrangement. The Na et Rb atoms are intercalating between their planes. The Fourier transform infrared spectrum exhibited characteristic bands corresponding to the tellurate and phosphate group. Thermal studies were carried out to examine the obtained material and yielded the presence of three phase transitions. The protonic conduction phase transition due to the presence of the breaking of O–H…O hydrogen bonds, was regarded as a technologically significant aspect for the new compound. These results corroborate that the new phosphate tellurate can be considered as a promising material in terms of enacting fruitful and constructive applications in advanced technology. The crystal structure was built up from corner-sharing TeOH₆ octahedrons, which intercalated by PO₄ tetrahedral units. These two groups are connected by hydrogen bonds which make up the building of the crystal, and the Na et Rb atoms are sandwitched between tetrahedral and Te(OH)₆ octahedral planes.