Ceramics-Silikáty 42 (2) 41-48 (1998)

DIELECTRIC PROPERTIES AND CURIE-WEISS BEHAVIOUR OF Pb(Zn_1/3Nb_2/3)O₃-PbTiO₃-PbZrO₃ CERAMICS

 V. Koval, J. Briančin, C. Alemany

The effects of the sintering temperature and the Pb(Zn_1/3Nb_2/3)O₃ content on the dielectric and piezoelectric properties of xPb(Zn_1/3Nb_2/3)O₃ - (1-x)Pb(Ti_0.53Zr_0.47)O₃ ternary system were investigated. In the case of the PZN - PZT ceramics with a low concentration of Zn_1/3Nb_2/3 (x = 0.05), the values of grain size (GS), Curie temperature (T_c ), mechanical factor of quality (Q_m), sintered density (ρ) and relative permittivity (ε_r ) increase as well as maximum relative dielectric permittivity at T_c (ε_max ), piezoelectric constants (d₃₃ , d₃₁ ) and radial coupling factor (k_p ) decrease with increasing sintering temperature (T_s ). The relative dielectric permittivity rises sharply with increasing temperature to a high peak value, ε_r ť 42 000, at the phase transition temperature, T_c ť 390°C. The introduction of a larger amount (x = 0.37) of Zn_1/3Nb_2/3 into the system resulted in the reduced permittivity (ε_max ť 9000) at the phase transition (T_c ť 290 °C) and the broadening of the dielectric peak response. The transition temperatures are frequency dependent and shifted towards a higher temperature with increasing sintering temperatures. An extended Curie-Weiss law is observed for 0.37PZN - PZT ceramics. The coefficient of diffusivity, γ ť 1.6 - 1.9, and the relative volume fraction of micro polar regions calculated from Keizer physical model are discussed from the view-point of diffuse phase transition in disordered systems. The observed lowering of the spontaneous strain as the PZN content increased has been pronounced with increasing sintering temperature and lead to the increase of the room-temperature relative permittivity, ε_r ť 3200, and piezoelectric parameters d₃₃ ť 410  ´ 10^-12 C N^-1 and k^p ť 49 %.

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