Influence of cyclic phase transitions on some properties of the ferroelectric perovskites Z. Surowiak a, *, S.V. Gavrilyachenko b , R. Skulski a , M.F. Kupriyanov b , D. Bochenek a a Silesian University, Faculty of Engineering, Department of Materials Science, 2 Sniezna Str., 41-200 Sosnowiec, Poland b Rostov State University, Faculty of Physics, 5 Zorge Str., 344-104 Rostov-on-Don, Russia Received 15 December 2000; received in revised form 9 October 2001; accepted 28 October 2001 Abstract The results of investigations of the influence of cyclic phase transitions on certain properties of the ferroelectric perovskites are presented. The materials were PZT-type ceramics obtained either by hot-pressing or by classical ceramic technology. It has been found that a close relationship exists between the concentration of linear defects and the stability of the resonant frequency as a function of temperature and time. The investigated samples can be divided into two groups: samples with high initial stability of resonance frequency and samples with low initial temperature stability. Our investigations show that in this two cases it is possible to distinguish three ranges of numbers of thermocycles, but the dependencies in the two cases differ one from the other. The change of concentration of defects and their distribution inside the crystallites lead to changes of temperature stability of resonant fre- quency.After5–6thermocyclesthestabilityincreases,butiftheinitialstabilityoftheresonantfrequencyishighthechangesaretoo small for practical applications. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Electrostriction; Fatigue; Perovskites; Piezoeletric properties; PZT; Thermocycling 1. Introduction The temperature stability of the resonant frequency is related to the domain structure and to the changes in the domain structure caused by external conditions. The mobility of domain walls is related to the presence of defects. 1 3 Such a conclusion is confirmed by the decrease of internal friction Q m 11 and the increase of coercive field E c 2 with increasing number of vacancies in the O 2 node points of the perovskite ABO 3 cell. Such point defects make the movement of domain walls more difficult (i.e. stabilize the domain structure). However, theinfluenceoflineardefectsondomainwallmobilityis bigger. 3 Around dislocations there exist strong electric fields as a result of the inflow of charged point defects (Debye’–Huckel atmosphere) and admixture atoms (Cotrell atmosphere). The higher the density of disloca- tions and the stronger the local electric fields, the more effective is the limiting of domain wall mobility by dis- locations. Consequently, there exists a close relationship between the concentration of linear defects and the temperature and time stability of the resonant frequency in materials used as piezoceramic electroacoustic trans- ducers. 4 The concentration of dislocations in ferroelectric ceramic samples can increase after heating to tempera- tures higher than the Curie temperature (T W >T C ) and following cooling down to room temperature (T r ). During such a heating/cooling cycle, the sequence of two phase transitions: ferroelectric (T < T C )$ para- electric (T > T C ) has taken place. During these phase transitions, the crystallites of the piezoceramic material undergo large mechanical tensions comparable with the tensions neede to exceed the elasticity limit of the mate- rial. These tensions favour change in the distribution of primary defects and the nucleation of new defects, especially dislocations. 5,6 The aim of this work was to examine how repeated heating and cooling of the sample through the Curie point, i.e. so-called thermocycling can influence the temperature stability of the resonant frequency f r , and the values of the basic dielectric and piezoelectric para- meters. 0955-2219/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0955-2219(01)00489-7 Journal of the European Ceramic Society 22 (2002) 1863–1866 www.elsevier.com/locate/jeurceramsoc * Corresponding author. Tel./Fax: +48-32-2918243. E-mail address: surowiak@us.edu.pl (Z. Surowiak).