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Thermo Raman studies and electrical properties of the Sr1.15Na1.7Nb4W1-xMoxO15 ceramics

Hicham. Es-soufi

The Sr1.15Na1.7Nb4W1-xMoxO15 (0≤x≤1) ceramics, labeled SNNbWM-x, were elaborated by the solid state route. Their structures were studied by X-ray diffraction and Raman spectroscopy and their electrical properties were investigated by impedance spectroscopy. X-Ray patterns of the ceramics reveal that the substitution of tungsten by molybdenum induces a full solid solution and the compounds crystallized in single-phase tetragonal tungsten bronze (TTB) with space group P4bm. Raman spectra of the SNNbWM-x compounds highlighted the vibration modes of the different cations involved in the TTB structure and showed a small peak’s displacement according to the Mo/W ratio. The Raman peak position temperature dependence studies had allowed to identify the presence of a phase transition around the temperature Te = 270°C in each compound. The investigation of the electrical properties of the SNNbWM-x samples in the frequency range 20 Hz–106Hz at various temperatures from room temperature to 550°C showed that theses ceramics exhibited a phase transition around 270°C in agreement with the thermo-Raman studies.