Physico-Chemical Studies of a New Zr-doped BaBeTiO3 System

Introduction

Since the discovery of the phenomenon of ferroelectricity, barium titanate BaTiO₃ was a standard material of the ferroelectric perovskite family. This compound has long been used in many industrial sectors such as electromechanical, the electronic and microwave applications ^{1, 2)} and electro-optical devices ³⁾. One of them, booming, is that of Multilayer Ceramic Capacitors MLCCs (Multilayer Ceramic Capacitors) ^4-11). An interesting and very current application of BaTiO₃ also relates to making computer memory frames (Ferroelectric Random Access Memories) ¹²⁾, the detection of polluting gases such as CO ¹³⁾ the optical waveguides, and holographic storage high frequency filters …) ^14-17) and the spatial light modulators ¹⁸⁾. This pure lead-free material and also strontium-doped, has a high environmental interest for applications mentioned above, due to its high dielectric constant value combined with relatively low voltage dissipation and wide tunability of the dielectric constant, as well as a good chemical stability ^19-21). Several studies have examined the effect of doping on the dielectric properties and relaxer behavior, in particular doping with Zr (BZT) and Sr (BSTZ) ^22-24). Recently, we investigated the effect of substitution of Zr in the Ti site (BaZr_xTi_1-xO₃) and reported the diffuse behavior in BZT (for x> 0.1) ²⁵⁾. Therefore, it would be interesting to study the effect of the substitution of Ti by Zr in other systems (nephews) as ((Ba_0.95Be_0.05) (Ti_1-xZr_x)O₃) (BBTZx). Thus, one aim of this work is the study of structural and dielectric properties of BBTZx ceramics; in particular, in this work, the attention has been focused on the evolution of the Cole-Cole diagram (ε’’ vs ε’) depending on the temperature of measurement.

Experimental methods

BBTZx ceramics samples with x = 0.075, 0.1, and 0.15 were prepared by the sol-gel method, using stoichiometric proportions of acetates of high purity: barium acetate (Ba(CH₃CO₂)₂; 3H₂O, purity 99:9%, Johnson Matthey GmbH Alfa, Karlsrube, Germany), beryllium acetate (C₁₂H₁₈Be₄O₁₃), zirconium acetate (Zr(CH₃CO₂)₄; xH₂O) (purity 99.9%, x = 1.5, Johnson Matthey GmbH Alfa, Karlsrube, Germany), and titanium alcoxide (97 % (Assay) Johnson Matthey GmbH Alfa, Karlsrube, Germany). Appropriate quantities of these precursors were thoroughly mixed in a woodshed, under continuous agitation at 60°C. And then calcined at 1273 K under an air atmosphere for 4 h, and then pressed into pellets of 12 mm diameter and approximately 1 mm thickness, under a uniaxial pressure of 10 ton. The pellets were then sintered at 1472 K for 8 h in air. Steps of the preparation of BT and BZT have been detailed elsewhere ^25-26). Phase identification of the samples was performed using X ray diffraction (Cu K ray, λ = 1.5418 Å). However to verify the stoichiometry of our samples, we used fluorescence spectroscopy technique. Dielectric measurements were carried out in the frequency range of 100 Hz to 2 MHz using an inductance capacitance resistance (LCR) bridge (HP, Model 4284 A).

Results and Discussion

Figure 1 shows XRD spectra of the BBTZx powders calcined at 1000 °C for 4 hours for different rates of Zr. It is observed that all powders crystallize in the perovskite phase with the presence of secondary microphase (BaCO₃); peaks associated with ZrO₂ (secondary phase) are not detected, indicating a complete incorporation of Zr ions into BT matrix. For x = 0 (Figure 1b) the presence of the peaks (200) and (002) is characteristic of the tetragonal phase ²⁷⁾, and with increasing Zr content they merge into one relatively large peak, which indicates a transition to the pseudo-cubic phase Moreover, a closer examination reveals that the increase in Zr content causes a displacement of the position of the peaks towards lower angles; the corresponding values of the 2θ position of the peak (111) of BBTZ_x are given in table I. This progressive displacement is attributed to the distortion (expansion) of BBTZ_x crystalline structure with increasing Zr rate due to the fact that the ionic radius of Zr^{4 +} (0.72 Å) is larger than that of Ti^{4 +} (0.605 Å).

Figure 1: XRD patterns of the powders BBTZx calcined at 1000 °C.  Click here to View figure

 

Table I. Lattice parameters a, 2θ of (111) peak and strain values of BBTZ_x.

Composition	2θ of (111) peak(°)	strain
BBT	38,3133	-0,99662
BBTZ7.5	38,2103	0,92744
BBT10	38,1763	0,93931
BBTZ15	38,1253	0,96327

Fig. 2 shows the plot of β cos θ as a function of sinθ for different percentages of Zr in BBT. A linear fit to these points gives an estimate of the nature of stress in these compounds. For BBT powders (without Zr) a linear fit (Figure.2) shows a negative slope whereas for BBTZ_x powders, it becomes positive. It is also found that the slope (positive) increases, which means an increase of the tensile stress in the BBTZ_x powders with increasing Zr content. However, for pure BBT powders (without Zr), the Be ion incorporation into the Ba sites creates a compressive stress due to smaller ionic radius of Be^{2 +} ions (0.45 Å) with respect to that Ba^{2 +} ions (1.35Å).

Results obtained from measurements using fluorescence spectroscopy technique are gathered in Table II showing an increase in atomic percent of zirconium and a decrease of that of titanium, pointing out a complete incorporation of Zr ions in place of Ti (B site in ABO₃ struture) ones in accordance of XRD results.

Figure 2: Constraint curve of BBTZx with different Zr contents. Click here to View figure

 

Fig. 3 displays Cole-Cole plots (from 1 kHz to 2 MHz) of the BBTZ_x samples at different temperatures. These Cole-Cole diagrams show depressed observed semicircles with their center lying below the real impedance axis which reveals a non Debye relaxation behavior with distributed relaxation times. This non-ideal behavior may be correlated to several factors such as grain size distribution, grain orientation and grain boundaries. It can also be observed that for the temperature 200°C (figure 4) the plots are depressed semicirculars in shape and their intercept on real axis shifts toward origin with increase in the rate of doping indicating the increase in the conductivity of the material. Moreover, substitution of Ti ions by Zr ones leads to distortions in the BBTZ_x structure. The literature reports that the ionic radius of Ba^{2 +} ions is about 1.34 nm, while that of Zr ⁴⁺ is 0.72 nm. According to this hypothesis, the substitution of Ti sites, often occupied by atoms of Zr, causes electronic compensation through the formation of barium gaps or oxygen which causes a decrease of the dielectric constant what is clear in table II.

Figure 3: Cole–Cole plots (ε’’vs. ε’) of different samples BBTZx at different temperatures Click here to View figure

 

Table II: The percentage of chemical elements obtained by fluorescence spectroscopy of BBTZx and ε_{max and} T_c.

Composition	Ba	Be	Ti	O	Zr	εmax	Tc(°C)
BT	36,42	0	35,57	28,01	0	6048	130
BBT	36,12	0.31	35,57	28,01	0	5599	125
BBTZ0.75	36,12	0.32	35,16	28,1	0,21	5402	110
BBTZ0.10	36,11	0.31	34,41	28,19	0,98	4682	100
BBTZ0.15	36,12	0.32	33,18	28,19	2,19	2633	80

Moreover, for pure BT, and for temperatures below 130°C (Fig. 3. a), one can notice that   the half-circles have an increasingly large diameter with increasing temperature. This tendency is however inverted above 130°C (Fig. 3. b). According to the literature ^28–31), this temperature (130°C), corresponds to the temperature of transition, Tc, from ferro-to-paraelectric phase. This observation is also valid for the other compounds at different concentrations in Zr. This result, which has never been reported in the literature, is observed due to the frequency measurement method, allowing determination of the transition temperature T_c without using other conventional methods consisting in collecting data for few frequency values which may prevent from observation of certain effects or phenomena.

Figure 4: Cole–Cole plots (ε’’vs.ε’) of different samples BBTZx at 200°C.  Click here to View figure

 

Conclusions

Pure and Zr-doped BBT ceramics were successfully prepared. XRD patterns Rietveld refinement revealed that these powders crystallize in the perovskite phase at room temperature. Dielectric measurements show that the temperature T_c and the dielectric constant decrease with increasing doping either by Be or Zr. Evolution of Cole-Cole diagrams (ε’’ vs ε’) revealed a non Debye relaxation behavior with distributed relaxation times. In this study we have given a new method to determine the fero-to-paraelectric temperature of transistion (T_c) based on the study of the thermal evolution of Cole-Cole diagrams (ε’’ vs ε’).

References

1. Cross, L.E.; Mater. Chem. Phys, 1996, 43, 108.
   CrossRef
2. Hiroshi, M.; Jpn. J. Appl. Phys, 2007, 46, 7013.
   CrossRef
3. Badapanda, T.; Panigrahi, S.; Rout, S.K.; Sinha, T.P.; Woo, S.I.; J. Korean Phys. Soc, 2009, 55, 749.
   CrossRef
4. Wereszczak, A. A.; Breder, K.; Ferber, M. K.; Bridge, R. J.; Riester, L.; And Kirkland, T. P.; American Ceramic Society, Cincinnati, Oh, 1998 .
5. Shin, Y. I.;  Kang, K. M.; Jung, Y. G.; Yeo, J. G., Lee; S. G., Paik, U.; J. Euro. Ceram. Soc, 2003, 23, 1427.
   CrossRef
6. Nakano, Y.; Nomura T.; And Takenaka, T.; Key Engineering Materials 2003, 248, 179.
   CrossRef
7. YOON, D. H.; LEE, B. I.; J. Euro. Ceram. Soc, 2004,.24, 753
8. Yokoi, H.; Wakiya, N.;  Shinozaki, K; And Mizutani, N.; Key Engineering Materials, 2004, 269, 229.
   CrossRef
9. Taïbi-Benziada, L.; Materials Science Forum, 2005, 492– 493, 109
10. Park, D. H.; Jung, Y. G.; Paik, U.; Ceramics International, 2005, 31, 655
    CrossRef
11. Scott, J. F.; Materials Science And Engineering B: Solid-State Materials For Advanced Technology, 2005, 120 (1-3), 6
    CrossRef
12. Zhou, D.; Chen, Y.; Zhang, D.; Liu, H.; Hu, Y.; Gong, S.; Sensors And Actuators A, 2004, 116, 450.
    CrossRef
13. Zhou, Z. G.; Tang , Z. L.; And Zhang, Z. T.; Key Engineering Materials. 2005, 369, 280
14. Iijima, K.; Tomita, Y.; Takayama, R.; and Veda, I.; J. Appl. Phys, 1986, 60, 361.
    CrossRef
15. Okada, M.; Takai, S.; Ameniyer, M.; Tominaya, K.; Jpn. J. Appl. Phys, 1989, 28, 1030.
    CrossRef
16. Li, A.H.; Zheng, Z.R.; Lü, Q.; Sun, L.; Xu, Y.H.; Liu, W.L.; Wu, W.Z.; Yang, Y.Q.; Lü, T.Q.; J. Appl. Phys, 2008, 104, 063526.
    CrossRef
17. Mccaughan, L.; Gill D.M.; US Patent, 1993, 5, 227.
18. Ishida, M.. Matsunami H.; and Tanaka, T.. Appl. Phys. Lett, 1977, 31, 433.
    CrossRef
19. Yu, Z.. Guo, R.. Bhalla, A.S.. J. Appl. Phys, 2000, 88, 410.
    CrossRef
20. Zhao, J.; Li, L.; Wang, Y.; Gui, Z.; Mater. Sci. Eng. B, 2003, 99, 207.
    CrossRef
21. Stojanovic, B.D.; Foschini, C.R.; Pavlovic, V.B.; Pablovic, V.M.; Pejovic, V.; J.A. Varela, Ceram, Int, 2002, 28, 293.
    CrossRef
22. Maiti, T.; Guo, R.; Bhalla, A.S.; J. Phys. D: Appl. Phys, 2007, 40, 4355.
    CrossRef
23. Kavita, V.; Seema, S.; Ceramics International, 2012, 38, 5957.
    CrossRef
24. Yanhua, F.; Shuhui, Y.; Rong. S.; Lei. L.; Yansheng. Y.; , Ruxu. D.; Thin Solid Films, 2010, 518,3610 .
25. Elbasset, A.; Abdi, F.; Lamcharfi, T.; Sayouri, S.; Abarkan, M.; Echatoui and, N. S.; Aillerie, M.; Indian Journal of Science and Technology, 2015, 8(13), 56574.
26. Elbasset, A.; Sayouri , S.; Adv. Mater. Lett, 2015, 6(11), 999.
    CrossRef
27. Zhang, J.; Zhai, J.; Chou, X.; Shao, J.; Lu, X.; Yao, X.; Acta Materialia, 2009, 57, 4491.
    CrossRef
28. Kim, S.W.. Choi, H.I.; Lee, M.H.; Park, J.S.; Kim, D.J.; Do, D.; Kim, M.H.; Song, T.K.; Kim, W.J.; Ceramics International, 2013, 39, S487.
    CrossRef
29. Darwish, A.G.A.. Badr, Y.. El Shaarawy, M.. Shash, N.M.H.. Battisha, I.K.. J. Alloys Compd. 2010, 489, 451.
    CrossRef
30. Horchidan, N.; Ianculescu, A. C.; Curecheriu, L. P.; Tudorache, F.; Musteata, V.; Stoleriu, S.; Dragan, N.; Crisan, D.; Tascu, S.; Mitoseriu, L.; J. Alloys Compd, 2011, 509, 4731.
    CrossRef
31. Kavian, R.; Saidi, A.; J. Alloys Compd, 2009, 468, 528.
    CrossRef

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