Microwave dielectric characteristics of (1-X) BaTi4O9-X Ba(Mg1/3Ta2/3)O3 ceramics

(1)

Journal of Alloys and Compounds 461 (2008) 404–409

Microwave dielectric characteristics of (1

− x)

BaTi

4

O

9

–xBa(Mg

1/3

Ta

2/3

)O

3

ceramics

Cheng-Fu Yang

a,∗

, Chien-Chen Diao

b

, Ho-Hua Chung

c

,

Hong-Hsin Huang

d

, Hua-Ming Chen

e

a_{Department of Chemical and Materials Engineering, National University of Kaohsiung, Kaohsiung, Taiwan, ROC} b_{Department of Electronic Engineering, Kao Yuan University, Kaohsiung, Taiwan, ROC}

c_{Department of Mechanical and Automation Engineering, Kao Yuan University, Kaohsiung, Taiwan, ROC} d_{Department of Electrical Engineering, Cheng-Shiu University, Kaohsiung, Taiwan, ROC}

e_{Institute of Photonics and Communications, National Kaohsiung University of Applied Sciences, Kaohsiung, Taiwan, ROC} Received 2 June 2007; received in revised form 28 June 2007; accepted 30 June 2007

Available online 21 August 2007

Abstract

The 1150◦C-calcined BaTi4O9powder (BT4) and 1200◦C-calcined Ba(Mg1/3Ta2/3)O3powder (BMT) are mixed to form the (1− x)BMT–xBT4 compositions (x = 0.18, 0.3, 0.45, 0.6, and 0.8), and the mixed (1− x)BMT–xBT4 compositions are sintered at 1240–1400◦C. The needed sintering temperatures of (1− x)BMT–xBT4 ceramics are lowered down to about 1280–1320◦C, which are lower than that of Ba(Mg1/3Ta2/3)O3ceramic is needed. The needed sintering temperatures of (1− x)BMT–xBT4 ceramics are almost independent on the BaTi4O9content. The morphologies changes from the disk-typed grains to two-phase structures, disk-typed grains and bar-typed grains coexist. The microwave dielectric characteristics of (1− x)BMT–xBT4 ceramics are developed in this study. It is found that the content of BaTi4O9has apparent effect on the crystal phase and the microwave dielectric characteristics of (1− x)BMT–xBT4 ceramics.

Keywords: Crystal growth; Dielectric response; X-ray diffraction

1. Introduction

A number of complex A(B1/3C2/3)O3 (A = Ba, Sr; B = Mg,

Zn, Ni; C = Nb, Ta) perovskite compounds had been devel-oped for high dielectric constant (25–40, εr values), high

unloaded frequency Q (>3000), and low temperature coeffi-cients of the resonant frequency (0± 40 ppm/◦C, τf values)

[1–5]. Ba(Mg1/3Ta2/3)O3 ceramics had a high quality value

(Qxf) and a low temperature coefficient of resonant frequency (τf). Unfortunately, the Ba(Mg1/3Ta2/3)O3ceramics formation

by the solid-state reaction of BaCO3, MgO, and Ta2O5was not

the most appropriate method, because high sintering temper-ature higher than 1600◦C was required to achieve sufficiently high sintered density and grain growth for the industrial applica-tions of the Ba(Mg1/3Ta2/3)O3materials. The poor sinterability

of Ba(Mg1/3Ta2/3)O3ceramics was thought to be hard

elimina-∗_{Corresponding author.}

E-mail address:cfyang@nuk.edu.tw(C.-F. Yang).

tion of some special satellite secondary phases of Ba5Ta4O15,

Ba4Ta2O9, and Ba7Ta6O22 from the solid reaction method

[6,7]. In order to eliminate such satellite secondary phases from Ba(Mg1/3Ta2/3)O3calcination, a recalcination process was

car-ried out [7]. Hence, it had an increasing importance in the suppressing or eliminating the satellite secondary phases and lowering down the sintering temperatures of Ba(Mg1/3Ta2/3)O3

ceramics.

Many efforts had been investigated to improve the sinter-ability of Ba(Mg1/3Ta2/3)O3 ceramics at lower temperatures

[8,9]. Chen et al. reported that Ba(Mg1/3Ta2/3)O3 ceramics

had a bulk density of 0.98 theoretical density, the value was obtained by adding NaF as sintering aid [8]. Tochi stated a new synthesis route using BaCO3 and MgTa2O6 as the

start-ing materials, and the addition of BaTa2O6 was effective in

improving the sinterability of Ba(Mg1/3Ta2/3)O3ceramics[9].

Numerous researches were also found that by the incorporation of Y2O3, Ba5Ta4O15 or other second perovskite type

mate-rials were beneficial for the formation of Ba(Mg1/3Ta2/3)O3

ceramics. Lin et al. presented that the sintered density of

(2)

408 C.-F. Yang et al. / Journal of Alloys and Compounds 461 (2008) 404–409

Fig. 6. The microwave dielectric constants of (1− x)Ba(Mg1/3Ta2/3)O3–x BaTi4O9ceramics, as a function of BaTi4O9content and sintered temperatures.

than those of BaTi4O9 ceramics reported. The εr values of

Ba(Mg1/3Ta2/3)O3 ceramics lower than those of BaTi4O9

ceramics will lead to this result. As the measurement in the bulk densities, we neglect the influence of unknown second phases. For that, the theoretical dielectric constants are calculated by using following equation:

_W 1 D1 + W2 D2 logε = W1 D1 logε1+W2 D2 log ε2 (3)

where W1/D1 and W2/D2 represent for the volume fraction

of Ba(Mg1/3Ta2/3)O3 ceramic and BaTi4O9 ceramic, and ε1

andε2represent dielectric constants of (Mg1/3Ta2/3)O3ceramic

and BaTi4O9ceramic, respectively, and the W1/D1+ W2/D2= 1.

The predicted dielectric constant can be calculated from the BaTi4O9ceramic of 38 and the Ba(Mg1/3Ta2/3)O3ceramic of

25. The predicted dielectric constant are 27.97, 29.76, 31.83, 33.71, and 35.98 for x = 0.18, 0.3, 0.45, 0.6, and 0.8; the mea-sured dielectric constant of (1− x)BMT–xBT4 ceramics are 27.2, 28.7, 30.2, 32.7, and 35.8, respectively. Even the existence of unknown second phases, the predicted dielectric constants of (1− x)BMT–xBT4 ceramics are close to the measured results.

The quality values (Qxf) and temperature coefficients of resonant frequency (τfvalues) of (1− x)BMT–xBT4 ceramics

are investigated as a function of BaTi4O9content and sintered

1320◦C, and the results are shown in Fig. 7. As the Fig. 7 shows, the BaTi4O9 content also has large effect on the Qxf

values and τf values. The Qxf values of (1− x)BMT–xBT4

ceramics first decrease with the increase of BaTi4O9

con-tent, reaches a minimum for x = 0.6 of Qxf = 34,800, and then slightly increases for x = 0.8 of Qxf = 34,800. The τf values

also increase with the increase of BaTi4O9 content. As the

BaTi4O9 content increases from x = 0.18 to 0.8, the τf

val-ues linearly change from 4.2 to 12.7 ppm/◦C. Because the Ba(Mg1/3Ta2/3)O3 and BaTi4O9 exist as two different phases

in the (1− x)BMT–xBT4 system, the Ba(Mg1/3Ta2/3)O3

com-position will dominate the microwave dielectric characteristics in the composition with high Ba(Mg1/3Ta2/3)O3content. In this

Fig. 7. The quality values and temperature coefficients of resonant frequency of (1− x)Ba(Mg1/3Ta2/3)O3–xBaTi4O9ceramics, as a function of BaTi4O9content and sintered 1320◦C.

study, the optimum Qxf = 66,600 andτfvalue = 4.2 ppm/◦C are

revealed in 0.82Ba(Mg1/3Ta2/3)O3–0.18BaTi4O9ceramics.

4. Conclusions

Even the (1− x)Ba(Mg1/3Ta2/3)O3–xBaTi4O9ceramics have

aτfvalue higher than Ba(Mg1/3Ta2/3)O3ceramics do, but theτf

values of BT4–BMT ceramics are lower than BaTi4O9ceramics

have. The addition of BaTi4O9 into the Ba(Mg1/3Ta2/3)O3 to

format (1− x)Ba(Mg1/3Ta2/3)O3–xBaTi4O9 compositions not

only decreases the satellite phases of Ba(Mg1/3Ta2/3)O3

ceram-ics but also improves the sinterability of Ba(Mg1/3Ta2/3)O3

ceramics. In this study, the BaTi4O9 content have large effect

on the bulk densities, the dielectric constants, the quality values, and the τf values of (1− x)Ba(Mg1/3Ta2/3)O3–xBaTi4O9

ceramics. In the (1− x)Ba(Mg1/3Ta2/3)O3–xBaTi4O9

sys-tem, the optimum Qxf = 66,600 and τf value = 4.2 ppm/◦C

are revealed in 0.82Ba(Mg1/3Ta2/3)O3–0.18BaTi4O9

ceramics.

Acknowledgment

The authors will also acknowledge to the financial support of the National Science Council of the Republic of China (contract NSC 95-2221-E-390-009).

References

[1] M. Onda, J. Kuwata, K. Kaneta, K. Toyama, S. Nomura, Jpn. J. Appl. Phys. 21 (1982) 1707.

[2] S.B. Desu, H.M. O’Bryan, J. Am. Ceram. Soc. 68 (1985) 546.

[3] S. Kawashima, M. Nishida, I. Ueda, H. Ouchi, J. Am. Ceram. Soc. 66 (1983) 421.

[4] O. Renoult, J.P. Boilot, F. Chaput, J. Am. Ceram. Soc. 75 (1992) 3337. [5] X.M. Chen, Y. Suzuki, N. Sato, J. Mater. Sci. Mater. Electron. 5 (1994)

244.

[6] T. Takada, S.F. Wang, S. Yoshjkawa, S.J. Jang, R.E. Newnham, J. Am. Ceram. Soc. 77 (1994) 1909.

[7] T. Takada, S.F. Wang, S. Yoshjkawa, S.J. Jang, R.E. Newnham, J. Am. Ceram. Soc. 77 (1994) 2485.

(3)

C.-F. Yang et al. / Journal of Alloys and Compounds 461 (2008) 404–409 409

[8] X.M. Chen, Y. Jwu, J. Mater. Sci. Mater. Electron. 7 (1996) 369. [9] K. Tochi, J. Ceram. Soc. Jpn. 100 (1992) 1464.

[10] M.H. Liang, C.T. Hu, C.G. Chiou, Y.N. Tsai, I.N. Lin, Jpn. J. Appl. Phys. 38 (1999) 71.

[11] I.N. Lin, M.H. Liang, C.T. Hu, J. Steeds, J. Eur. Ceram. Soc. 21 (2001) 1705.

[12] C.M. Cheng, Y.T. Hsieh, C.F. Yang, Mater. Lett. 57 (2003) 1471. [13] W.C. Tzou, C.C. Chan, P.S. Cheng, C.F. Yang, J. Mater. Sci. (2005) 4711. [14] B.W. Hakki, P.D. Coleman, IEEE Trans. M.T.T. 8 (1960) 402.

[15] W.E. Courtney, IEEE Trans. M.T.T. 18 (1970) 476.

[16] C.M. Cheng, C.F. Yang, S.H. Lo, T.Y. Tseng, J. Eur. Ceram. Soc. (2000) 1061.