Abdelhedi Aydi

Structural and dielectric properties of (Ba 1−x Sr x ) 0.93 Na 0.07 Ti 0.93 Nb 0.07 O 3 ceramics

Abstract(Ba1−xSrx)0.93Na0.07Ti0.93Nb0.07O3 ceramics with different compositions (xu2009=u20090.15; 0.2; 0.25; 0.4) were synthesized by a conventional solid-state reaction at 1470u2009°C for 2xa0h (h). Phase purity, structure and crystallinity were investigated with X-ray diffraction at room temperature, showing pure phases with tetragonal symmetries for (xu2009=u20090.15, 0.2) and cubic for (xu2009=u20090.25, 0.4). The real part of the relative dielectric permittivity

Structural, dielectric and impedance spectroscopy studies of (Na 0.5 Bi 0.5 )(Zr 0.025 Ti 0.975 )O 3 ceramic

varepsilon _{{rm}}^{}

X-ray and dielectric studies of ferroelectric or relaxor phases in the Ca1−xNaxSn1−xNbxO3 system

εrm′ exhibited a sharp peak with no frequency dependence, which revealed a ferroelectric relaxor behavior for all compositions with a diffuse phase transition and frequency dispersion. The evolution of the Raman spectra, at room temperature, shows an introduction of disorder in this composition, thus favoring a ferroelectric relaxor behavior.

X-ray diffraction, dielectric measurements and Raman spectroscopy: Studies of the (1 − x)CaSnO3 − x NaNbO3 solid solution

Lead-free (1xa0−xa0x)NaNbO3/xBa(Ti0.5Sn0.5)O3 (xxa0=xa00.1, 0.125, 0.15, 0.175, 0.2, and 0.3) ceramics were elaborated by the conventional ceramic technique. Sintering has been made at 1523xa0K for 2xa0h. The crystal structure was investigated by X-ray diffraction with CuKα radiation at room temperature. As a function of composition, these compounds crystallize with tetragonal or cubic symmetry. Dielectric measurements show that the materials have a classical ferroelectric behavior for compositions in the range 0.10xa0≤xa0xxa0≤xa00.15 and relaxor one for compositions in the range 0.15xa0<xa0xxa0≤xa00.30. Temperatures TC or Tm decrease as x content increases. The ferroelectric behavior has been confirmed by hysteresis characterization. For xxa0=xa00.1, a piezoelectric coefficient d31 of 42.146xa0pCxa0N−1 was obtained at room temperature. The evolution of the Raman spectra was studied as a function of temperature for xxa0=xa00.1.

Elaboration and dielectric study of ferroelectric or relaxor ceramics in the ternary system BaTiO3–NaNbO3–BaSnO3

Structural, vibrational, dielectric and electrical properties of (Na0.5Bi0.5)(Zr0.025Ti0.975)O3 ceramic synthesized by the solid-state reaction technique have been carried out. The X-ray diffraction analysis was indicated as a pure perovskite phase in the rhombohedral structure. The modes of rhombohedral vibrations were appeared in the experimental Raman spectrum at room temperature. The dielectric and electrical properties of the material were investigated by impedance spectroscopy analysis for a broad range of temperatures (50–560xa0°C) and frequency domain of 102−106xa0Hz. The dielectric measurement exhibit two phase transitions: a ferro-antiferroelectric transition followed by an antiferro-paraelectric transition at higher temperatures. Complex impedance analysis was carried out in order to distinct the contribution of the grains and the grain boundaries to the total electrical conduction. The Nyquist plot was proved to be a non-Debye relaxation mechanism. The combined spectroscopic plots of the imaginary part of electric impedance and modulus confirmed the non-Debye type behavior. The frequency dependent ac conductivity obeys the double power law behavior and shows three types of conduction process. The significant decrease of dc conductivity spectrum followed the Arrhenius relationship. The values of calculated activation energy of the compound implied that the electrical conduction is mostly due the high oxygen mobility.