The temperature dependences of electromechanical properties of PLZT ceramics

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1 The headers will be insert by the Publisher The headers will be insert by the Publisher The headers will be insert by the Publisher The teperature dependences of electroechanical properties of PLZT ceraics Marek CZERWIEC and Radosław ZACHARIASZ Jan ILCZUK Faculty of Coputer Science and Material Science, Departent of Material Science, University of Silesia, 3 Żeroskiego, 4-2 Sosnowiec, POLAND, arek.czerwiec@orange.pl Abstract. The echanical and electrical properties in lanthanu odified lead zirconate-titanate ceraics of 5/5/5 and /5/5 were studied by echanical loss Q -, Young s odulus E, electric perittivity ε and tangent of dielectric loss of angle tgδ easureents. The internal friction Q - and Young odulus E easured fro 29 K to 6 K shows that Curie teperature T C is located at 574 K and 435 K ( st cycle of heating) respectively for ceraic saples 5/5/5 and /5/5. The oveent of T C in second cycle of heating to lower teperature (56 K for 5/5/5 and 42 K for /5/5) has been observed. Together with Q - and E easureents, teperature dependences of ε=f(t) and tgδ=f(t) were deterinate in teperature range fro 3 K to 73 K. The values of T C obtained during ε and tgδ easureents were respectively: 56 K for 5/5/5 and 49 K for /5/5. These teperatures are alost the as teperatures obtained by internal friction Q - easureents in second cycle of heating. In ceraic saple /5/5 the additional axiu on internal friction Q - curve at the teperature 36 K was observed.. INTRODUCTION Pb(Zr, Ti)O 3 (PZT) crystallizes with the ABO 3 type structure in which the A-site is occupied by Pb 2+ ions; Zr 4+ and Ti 4+ are accoodated on the B-site. The influence of various substitutions in the A and B-site of PZT unit cell has been studied by nuerous investigators in order to odify the properties of the aterials for device applications such as non-volatile eories, transducers, odulators, etc. Modification of the PZT syste by the addition La 3+ ions has arked beneficial effect on several the basic paraeters, such as squerness of the hysteresis loop, decreased coercive filed, increased dielectric constant, axiu coupling coefficients, increased echanical copliance, and enhanced optical transparency [-4]. 2. EXPERIMENT The aterial tested were solid solution of the PLZT fro ferroelectric phase with constant ratio Zr/Ti=5/5 and variable concentration of La 3+ ions : Pb,95 La,5 (Zr 5 Ti 5 ),9875 O 3 - PLZT 5/5/5 and Pb,95 La, (Zr 5 Ti 5 ),975 O 3 - PLZT /5/5.

2 2 JOURNAL DE PHYSIQUE IV Ceraic saples were obtained as a reaction in solid state fro siple oxides: PbO, ZrO 2, TiO 2, La 2 O 3 by conventional ceraic sintering (CCS) ethod. Ceraic powders were ixed and illed through 2h and next fored in cylindrical tablets of diaeter. After this tablets were synthesized at the teperature T S = 23K through t s = 6h. Then polycrystalline saples were crubled and ixed to obtained ore hoogenous structure. The range of sintering teperatures (223 K 523 K) and sintering ties (6h 2h) were dependable fro cheical coposition. The electrodes were deposited on the surface of PLZT saples by the silver paste burning ethod. The obtained saples were subjected to polarization using the low teperature ethod (T p = 423 K, E p = 3 kv/c, t p = 3 in). The easureent of dielectric perittivity ε and tangent of dielectric loss of angle tgδ were obtained by the capacity bridge BM 57/538 Tesla type with frequency khz and teperature range between 3 K and 73 K. Teperatures dependences Q - (T) and E (T) were perfored by autoatic resonance spectroeter RAK-3 type controlled by coputer. 3. RESULTS AND DISCUSSION On the fig. teperature dependences of Q - (T) and E(T) are presented. For the coposition 5/5/5 the easureents were ade during two cycle of heating with different resonance frequency (f r ) of saple vibration. In the roo teperature the values of f r were respectively: 838 Hz for st cycle of heating and 8 Hz for 2 nd cycle. E [GPa] Q - x 3 [-] M' R M'F 5/5/5 st cycle of heating 5/5/5 2 nd cycle of heating /5/5 st cycle of heating /5/5 2 nd cycle of heating P 3 F P' P' F 5 R M F Figure. The teperature dependences of Q - (T) and E(T). for PLZT tested saples.

3 Colloque short title 3 Siilarly for /5/5 coposition, f r were 9 Hz and 866 Hz. All easureents were conducted with 3K/in ratio of heating. Both for saples 5/5/5 and /5/5 after st cycle of heating, clearly axia P F i P F on the curves Q - (T) were observed. The axia correlated with inia M F i M F observed on E(T) curves. Those changes were observed in teperatures: T F = 574 K i T F = 435 K. After deep analysis of phase diagra of PLZT syste was proved that the teperatures are responsible for phase transition ferroelectric paraelectric (Curie teperature T C ) [2]. In the 2 nd cycle of heating was observed clearly increase of height of peaks P F i P F and their little oveent to lower teperatures: T F = 56 K for PLZT 5/5/5 and T F = 42 K for PLZT /5/5. In the references of the earlier works authors proved that behavior like this of the axi Q - (T) in the areas of phase transitions is ainly connected with phenoena described by the Delore and Gobin odel [5,6]. Additionally for coposition PLZT /5/5 at curve Q - (T) axiu P R was observed in teperatures 36 K and 322 K respectively for st and 2 nd cycle of heating. The way of behavior of this axiu and paraeters calculated by the Arrhenius law: energy of activation H = 2,33 ev and preexponential τ = 5-29 s - proved that origin of the axiu is connected with ore coplicated processes and it will be subject of future researches. 2 5/5/5 /5/5,4,3 8 ε [-] 6,2 tg δ [-] 4 2,, Figure 2. Zależności ε(t) and tgδ(t). The easureents of the teperature dependences of ε(t) and tgδ(t) were obtained as a ai of detailed analysis of the changes in the area of phase transition. The results of investigation are shown at the figure 2. The nature of the teperature dependences of tgδ(t) in the range of teperatures below phase transition is connected with dissipation of energy to polarization of the doains. But above the phase transition teperature (T C ) losses of energy are related with electric conductivity. For both cheical coposition of PLZT type ceraics the teperature dependences of ε(t) has a relaxor character with diffuse phase transition between ferroelectric and paraelectric phase. The linear and quadratic Curie-Weiss laws were used to analysis of the dependences of /ε (T). At the paraelectric phase above teperature T (PLZT 5/5/5) i T (PLZT /5/5), the linear Curie-Weiss law was used [7]: + CCW = T T ε ()

4 4 JOURNAL DE PHYSIQUE IV where: C + CW Curie-Weiss constant, In the ferroelectric phase Curie-Weiss law: where: C - CW Curie-Weiss constant, C = T CW ε (2) T The values of the Curie-Weiss constants as well for paraelectric and ferroelectric phase are presented in table. The range of teperatures T -T 2 is responsible for relaxor diffuse phase transition. In the range of teperatures between T and T experiental curves of dependences ε(t) are described by quadratic Curie-Weiss law [8]: ε γ = = K( T T ) * (3) ε ε where: ε electric perittivity at the teperature of phase transition T. /ε x a) T ' T 3 T ' 4 5T T T ' 5/5/5 /5/5-3,5-4, b) 5/5/5 /5/5 log (/ε-/ε ) [-] -4,5-5, -5,5-6, -6,5,4,6,8,,2,4,6,8 2, 2,2 log (T-T ) γ [-] Figure 3. The dependences /ε (T) fig 3a and log(/ε /ε )=f(log (T T ) γ ) fig 3b.

5 Colloque short title 5 4. CONCLUSIONS Obtained PLZT type ceraic saples are characterized by low values of tangent of dielectric loss of angle tgδ=,5% and high values of electric perittivity ε= 2 (at roo teperature). The easureent of the teperature dependences of Q - and E let to obtained the teperature of phase transition (T C ). The value of T C is decreasing with increasing of La content. Lanthanu has also significant influence for level of diffuse phase transition. References [] Evans T. J., Woack R., IEEE J. Solid State Circuits 23 (988) 7. [2] Haertling G. H., J. A. Cera. Soc. 82 (4) (999) 797. [3].Bouri E. M, Tanaka H., Gabbay M., Fantozzi G., Cheng B. L., J.Appl. Phys. 9 (22) [4] Hulang C. L., Chen B. H., Wu L., Solid State Co. 3 (24) 9. [5] Delore J.F., Gobin P.F., Metaux, Corr. Ind. 573 (973) 85. [6] Bartkowska J.A, et. all., J. de Phys. IV (26). [7] Pilgri S., Audrey M., Sutherland E., Winzer E.R., J. A. Cera. Soc. 73 (99) 322. [8] Z.-Y. Cheng, R.S. Katiyar, X. Yao, A. Guo, Phys. Rev. B 55 (997) 865.