Search

The copper hydrogeno-arsenite tellurate material (CuAsTe) was synthesized and its magnetic properties were investigated. Thermal analyses revealed that no mass loss was recorded before 480 K. Additionally, in this current work, electrical properties based on the impedance measurements were determined. The complex impedance diagram at different temperatures demonstrated a single semicircle, implying that the response originated from a single capacitive element corresponding to the grains. The thermal evolution of the conductivity ¿dc displayed an Arrhenius type behavior and suggested that this material is an ionic protonic conductor at high temperature whereas the ¿ac conductivity was indicative that the conduction mechanism is ensured by the correlated barrier hopping (CBH) model. The variation of M¿ versus frequency proved to be a thermally activated dielectric relaxation process. Notably, we specified determined the direct optical band gap Eg = 2.3 eV in order to characterize the optical properties.

The thermal study DSC, TG, dTG, DTA, Ms 18/H2O and Ms 15/NH3 reveal the presence of two-phase transitions at T = 401 K and 463 K before the decomposition which takes place at T = 485 K through the check of five water and two ammonia molecules. The structural study at high temperature T = 410 K and the spectroscopic evolution with the temperature prove that the first transition is of order-disorder and structural type. Basically, using the Tauc model, we determined the direct optical band gap Eg=2.11 eV so as to characterize the optical properties.

Thermal analysis confirmed the presence of the phase transition at T = 320 K in the Cs2SeO4·H6TeO6 (CsSeTe) material. The structural study carried out at T = 360 K shows that this compound passes from the monoclinic system with the space group P21/c at room temperature, to the trigonal system with the space group R3¯m. At room temperature, the anionic groups are well ordered and stable, whereas after the transition at T = 320 K, the selenate groups change their orientation and the tellurate polyhedra change their positions. The high-temperature vibrational studies, carried out in a temperature range of 289–353 K, confirm the presence and nature of the transition detected by thermal analysis. The conductivity evolution versus temperature shows the presence of an ionic–protonic conduction phase transition at T = 490 K.

Our central focus is upon the effect of chemical preparation of the cesium hydrogen–arsenate tellurate material. This compound was synthesized by slow evaporation in two different conditions. X–ray diffraction analyses revealed a monoclinic system for both preparations. With centrosymmetric space group P21/c, (CsAsTe 1) material was elaborated in a cold temperature condition (CTC) [12–18 °C]. However, in a hot temperature condition (HTC) [32–38 °C], (CsAsTe 2) compound crystallizes in the non–centrosymmetric space group Cc. The increase in temperature affects the structural arrangement in which the coordinated polyhedra are distorted. Moreover, Hirshfeld surface analyses were performed to explore the intermolecular interactions in the two crystals lattices. The DSC thermograms highlight the presence of three phase transitions before the decomposition for each compound. These two materials present an ionic–protonic conduction phase transition with two different behaviors.

Cesium sulfate arsenate tellurate (CsSAsTe) presents one reversible phase transition of the first-order type at 213/211 K on heating–cooling runs. Indeed, it crystallizes at T = 120 K in the monoclinic system P21/c and at T = 275 K, in the trigonal system R3c. These crystal structures are built from isolated (HAsO2_4 SO2_4) tetrahedra and (TeO6_6) octahedra, they form tunnels where Cs+ cations and some hydrogen atoms are placed. The cohesion of these structures is assured on the one hand by the interaction between Cs+ and the oxygen atoms and on the other hand, by the presence of hydrogen bonds.

A new compound from the tellurate family was synthesized under a slow evaporation conditions. A crystalline sample of Cs2(HAsO4)0.32(SO4)0.68·Te(OH)6 (CsAsSTe) was calorimetric and spectroscopically characterized. The infrared and Raman spectra of this new compound recorded at room temperature, in the frequency range 500–4,500 and 50–1,500 cm−1, respectively, confirm the presence and the independence of two types of anion HAs/SO4 and TeO6. The thermal analysis of the title compound shows one endothermal and intense peak at 512 K accompanied by a shoulder at 506 K. However, the conductivity evolution versus temperature showed the presence of the protonic super conduction phase transition. The conductivity relaxation parameters of some H+ and Cs+ conducting in the CsAsSTe material have been determined from an analysis of ac conductivity data measured in a wide temperature range. Transport properties in this compound appear due to H+ ions hopping mechanism.