Electrical properties of the ferroelectric bulk in europium-modi®ed lead titanate ceramics O. Pe Ârez Martõ Ânez * , F. Caldero Ân Pin Äar, A. Pela Âiz Barranco Facultad de Fõ Âsica, Instituto de Materiales y Reactivos, Universidad de la Habana, San La Âzaro y L, Vedado, Havana 10400, Cuba Received 7 July 2000; accepted 6 November 2000 by R.C. Dynes Abstract By using impedance spectroscopy technique we have investigated temperature dependence of various dielectric parameters in Pb 0.88 Eu 0.08 Ti 12y Mn y O 3 ceramic system. Two contributions R 1 C 1 and R 2 C 2 , which contain the AC response of the ferroelectric bulk were observed for the ®rst time in the modi®ed lead titanate ceramics. Microstrains originating from structural defects in unpoled samples are responsible for the electrical inhomogeneity observed in the ferroelectric grains, which should worsen after poling process; this was followed by the piezoelectric anisotropy observed in modi®ed lead titanate. q 2001 Published by Elsevier Science Ltd. Keywords: A. Ferroelectrics; D. Dielectric response; D. Phase transitions; D. Piezoelectricity PACS: 77.84.Dy; 77.80.Bh; 77.22.Ch; 77.22.Gm 1. Introduction As far as we know, dense ceramics could be obtained by the partial substitution of rare earth elements in modi®ed lead titanate. In particular, the substitution of lead by europium provokes a large anisotropy of the piezoelectric effect k t =k p ! 1 in Pb 0.88 Eu 0.08 Ti 12y Mn y O 3 ceramics. This peculiar property makes these ceramics suitable for use in high-frequency array transducers since the spurious wave generation in the acoustic signal is very small for lateral vibration, in contrast with traditional transducer based on the PZT ceramic system [1]. The introduction of Eu into lead titanate produces one lead vacancy for every two Eu 31 ions. These defects locally break the translational periodicity of the lattice. Consequently, the long-range interaction between ferroelectrically active octaedra containing B-site cations is affected. It should be noted that these ceramics also require a modi®cation on the B site to produce optimum electromechanical anisotropy k p ! 0: The introduction of some amount of Mn increased this breaking; it is due to new structural defects (oxygen vacancies) produced by Mn 41 /Mn 21 reduction, during the sintering process [2]. The breaking in the translational periodicity can be observed in the nonuniform variance of the tetragonality c=a; the large microstrains and a detri- ment of crystallinity of these ceramics. A large microstrain originated by structural defects in unpoled samples seemed to play a crucial role in the attainment of large piezoelectric anisotropy in the system [1]. This behavior evidently must in¯uence the electrical response of the ceramic system, which is the principal objective of this study: applying the variable-frequency techniques of impedance spectroscopy to the europium-modi®ed lead titanate system. AC impedance methods are widely used to characterize electrical materials. Data may be analyzed in terms of four possible complex parameters, the impedance Z p , the electric modulus M p , the admittance Y p and the dielectric permit- tivity e p . The useful separation of intergranular phenomena from bulk phenomena depends ultimately on the choice of an appropriate equivalent circuit to represent the sample properties. We have used model equivalent circuits [3,4] to simulate, in the complex impedance plane, the effects of blocking electrodes, grain boundaries, etc. It is usually possible to ®nd more than one equivalent circuit that ®ts, numerically, a given data set, but only one of these is likely to provide a realistic representation of the electrical behavior of the sample. Solid State Communications 117 (2001) 489±493 0038-1098/01/$ - see front matter q 2001 Published by Elsevier Science Ltd. PII: S0038-1098(00)00495-6 PERGAMON www.elsevier.com/locate/ssc * Corresponding author.