Alternating-current impedance spectroscopic studies were carried out at 550 to 700C on undoped and Mn-doped PZN-PT single crystals grown by using the flux method. The variation of dielectric permittivity with temperature at various frequencies revealed normal ferroelectric and relaxor-like dependences of the doped and undoped crystals, respectively. Temperature-dependent spectroscopic modulus plots revealed a much broader peak for PZN-4.5PT-1%Mn, as compared with that for PZN-4.5PT, which was different to the dielectric behavior of the doped material. Complex modulus, imaginary versus real part plots, fitted one semicircle well; thus indicating only a bulk contribution. The relaxation observed in the spectroscopic plots was attributed to mobile relaxor species such as O vacancies and ions. No similar relaxation could be observed for PZN-4.5PT-1%Mn in the dielectric measurements. For both undoped and Mn doped crystals, the conduction behavior was modelled by the universal dynamic response equation and by a negative temperature coefficient material resistance-temperature behavior. A large difference in behavior was found between the two single crystals, with respect to the thermistor coefficients and the activation energy values. This could explain the increase in thermal stability often observed in Mn-doped PZN-PT single crystals.

Oxygen Vacancies Effect on Ionic Conductivity and Relaxation Phenomenon in Undoped and Mn-Doped PZN-4.5PT Single Crystals. D.Kobor, B.Guiffard, L.Lebrun, A.Hajjaji, D.Guyomar: Journal of Physics D, 2007, 40[9], 2920-6