Dielectric Properties of Zirconium Tin Titanate with Additives of

Dielectric Properties of Zirconium Tin Titanate with Additives of

ZnO, CuO, MnCO 3 and Bi 2O 3

H.G. Yu, C.X. Song, Z.H. Shen and Z.X.Xiong *

Department of Materials Science and Engineering, Xiamen University, Xiamen 361005, china Keywords: ZST ceramics, Dielectric properties, Sintering additive, Microwave ceramics

Abstract. (Zr 0.8Sn 0.2)TiO 4 ceramics with additives of ZnO, CuO, Bi 2O 3 and MnCO 3 were prepared by the conventional mixed oxide route. They were characterized by TG/DTA, SEM, EDS and a network analyzer. Microwave properties of (Zr 0.8Sn 0.2)TiO 4 ceramics were investigated as a function of the amount of additives. The optimal values of dielectric constant εr , quality factors Q*f and temperature coefficient of resonant frequency τf reached 35, 51000 GHz and 26 ppm/°C respectively with 2.0 wt% MnCO 3. Specimens with additives of ZnO, CuO and Bi 2O 3 had microwave properties of εr = 35 ~ 39, Q*f = 9000 ~ 35000 GHz and τf = 15~40 ppm/°C.

Introduction

Recently zirconium titanate based ceramics, especially the (Zr 0.8Sn 0.2)TiO 4 (defined as ZST) ceramics, have attracted much interest for its high dielectric constant εr , high quality factor Q and low temperature coefficient of resonant frequency τf . In order to accommodate the rapid growth of the wireless communication industry, the ZST ceramics are used as dielectric resonators ranging from cellular phones to global positioning systems [1-3].

The structure of ZrTiO 4 is an orthorhombic system of α-PbO 2 type [4], the space group Pbcn [5]. In the normal phase of ZrTiO 4, the Zr ion and the Ti ion are randomly distributed on the octahedral sites in the α-PbO 2 type structure, as shown in Fig. 1.

Being difficult to fully densify ZST ceramics, there is considerable interest in the development of materials with low sintering temperature. A combination of two or more oxides are used as sintering aids, such as La 2O 3, BaO, ZnO, Co 2O 3, V 2O 5 and CuO [6-8]. With proper amount of additions, the ceramics can be well sintered to approach 96% of theoretical densities at 1300°C due to liquid phase effect [9]. In this paper, ZnO, CuO, Bi 2O 3 and MnCO 3 were used as sintering aids. The microwave dielectric properties of ceramic materials were investigated with respect to the crystallographic structure, porosity and grain size. The effects of the amount of additives on the microwave dielectric properties of (Zr 0.8Sn 0.2)TiO 4 ceramics were reported.

Experimental procedures

The ceramics were prepared via the conventional mixed oxide route. The raw materials ZrO 2, SnO 2, ZnO, CuO, Bi 2O 3 and MnCO 3 were high purity (> 99%) and TiO 2 was a little lower (> 98%). These powders were weighed in according to desired stoichiometry of ZST ceramics and then ball-milled for 4h with distilled water and zirconia balls. The mixtures were dried and calcined at 1100°C for 2h. Certain amount of ZnO, CuO, Bi 2O 3 and MnCO 3 were added into the calcined powders and re-milled for 2h, then dried and granulated with PVA solution as a binder. The powders were uniaxially pressed into disks by a pressure of 150 MPa and then sintered at temperatures from

*

Corresponding author. E-mail address: zxxiong@https://www.360docs.net/doc/3217821458.html,

Fig. 1 Chemical structure of ZrTiO 4

Key Engineering Materials Vols 280-283 (2005) pp 91-94Online:2007-02-15

? (2005) Trans Tech Publications, Switzerland doi:10.4028/https://www.360docs.net/doc/3217821458.html,/KEM.280-283.91

1200~1400°C for 2~6h.

TG and DTA curves of the powders were obtained from room temperature to 1300°C at a rate of 10°C/min with a thermal analyzer in air atmosphere. The crystalline phases of the sintered specimens were determined by XRD analysis. The sintered densities of the samples were measured by the Archimedes method. The specimens were observed for their microstruc- ture by means of

SEM equipped with EDS . The microwave

dielectric properties were measured by a network

analyzer. The temperature coefficient of resonant frequency τf was determined with a network

analyzer equipped with a thermostat in the temperature range –20~80°C.

20

30

4050

60

7080

200

400600800100012001400

1600180020002200T c =1000??

T c =1100??

??

??

??

??

??

????

??

u

u u

u

T i O

2

S n O

2

Z r O 2u

u

*

*

*

*

*

*h

h

h

h

h

h

h

￡¨Z r

0.8

S n

0.2

)T i O

4

i n t e n s i t y

2-T h e t a

Fig. 3 XRD patterns of the ZST powder calcined at different temperature

jjjj

S e c o n d p h a s e

Fig. 4 XRD patterns of ZST ceramics with different amount of MnCO 3 additive

Results and discussion

TG/DTA curves were obtained for the mixed powders in the stoichiometric proportions of ZST as shown in Fig. 2. There was an endothermic peak above 1100°C. This may be due to the formation of the main crystalline phases of the ZST system.

It could be seen in Fig. 3 that ZST phases formed initially at 1000°C, considerably at 1100°C. XRD patterns of ZST ceramics with different amount of MnCO 3 additives, shown in Fig. 4, were similar in the main phase. At the level of 0.5 ~ 1.0 wt% MnCO 3 additives, ZST ceramics exhibited almost a single phase. However, second phase was detected in the specimens with 1.5~2.5 wt% MnCO 3. As the density of the second phase was lower than that of the main phase, the relative density of the ceramics decreased. This was confirmed by the curve of the relative density, shown in Fig. 5, which inclined down- wards slightly

with the increasing amount of MnCO 3 from 1.5 to 2.5 wt%.

However, the relative density increased dramatically when

the amount of MnCO 3 increased from 0.5 wt% to 1.5 wt%.

The results were also confirmed by the microstructure of

the samples in Fig. 6. There was 0.95 wt% Mn element in

the glass phase of ZST ceramics with 1.5 wt% MnCO 3, but

when the amount of MnCO 3 was 0.5 wt%, Mn element was

not detected by EDS analysis on the grain boundaries. The

amount of Mn element increased with the increasing of

additives. Compared with the size of the grain in Fig. 6 (a),

the grain in Fig. 6 (b) was larger.

Fig. 7 showed the dielectric properties of ZST ceramics with various amount of additives. The dielectric constants (εr ) reached a maximum value of 38 with 1.5 wt% MnCO 3.

It maybe resulted from the maximum value of density and large grain size with the same amount of MnCO 3, as confirmed by Fig. 5 and Fig. 6. This was also in agreement with the result by Takata et al. [10]. The quality factors (Q*f) reached the maximum value of 51000 GHz with 2.0 wt% MnCO 3. As the unloaded Q is almost not affected by the density if the relative density is greater than 90% of the theoretical density [11], the increasing of the unloaded Q with MnCO 3 additive may resulted from the decreasing of the porosity as confirmed in Fig. 6. At the same time, the temperature coefficient of resonant frequency for the ceramics with 2 wt% MnCO 3 additive showed a value τf = 26 ppm/°C.

(a) MnCO 3 wt%=0.5%, 1360°C * 2 h Mn wt% = 0.00%

(b) MnCO 3 wt%=1.5%, 1320°C * 2 h Mn wt% = 0.95%

Fig. 6 SEM photographs of ZST ceramics with EDS

analysis

Physical properties of ZST ceramics with additives of ZnO, CuO, Bi 2O 3 and MnCO 3 were listed in table 1. Although the specimens were quite densified, the Q*f values were not high enough compared with those of samples added only with MnCO 3. This illustrated that the unloaded Q was closely related to the amount and the type of the additives.

Summary

The maximum dielectric constant value εr = 38 was reached with 1.5 wt% MnCO 3, while the maximum quality factors Q*f = 51000 GHz was obtained with 2.0 wt% MnCO 3. The dielectric constant mainly de-

Table 1 Physical properties of ZST ceramics with additions.

Specimen

ZrO

(wt%)

CuO

(wt%)

Bi2O3

(wt%)

MnCO3

(wt%)

TD% εr

Q*f

(GHz)

τf

(ppm/°C)

1 2 3 4 5 6 7 8 9 10

0.2

0.2

0.5

1.0

1.0

1.0

1.0

0.5

0.5

0.5

0.5

0.5

0.3

1.0

1.0

0.1

1.0

0.5

1.0

2.0

1.0

96.8

94.7

96.5

96.7

94.4

95.9

98.2

98.5

97.6

97.8

39.1

36.9

37.7

37.4

34.7

37.5

36.6

37.8

37.5

35.6

31382

24259

35475

22961

10682

31211

26561

25740

9034

30276

28

15

25

37

19

pended on density of the ceramics. However, the quality

factors not only depended on the ceramic density, but

also largely depended on porosity. The unloaded Q

value of the specimens with MnCO3 was showed higher

than that of the specimens with ZnO, CuO and Bi2O3.

The temperature coefficient of the resonant frequency τf

= 26 ppm/°C with 2.0 wt% MnCO3.

Acknowledgements

This work was supported by the National High-Tech

Research and Development Plan of China (“863” Plan)

under Grant No.2001AA325100.

References

[1]Y. Higuchi and M. Katsube: US Patent, 4665041 (1987).

[2]Y. Park, N.H. Cho and Y.H. Kim: US Patent 5432134 (1995).

[3]S.I. Hirano, T. Hayashi and A.Hattori: J. Am. Ceram. Soc. Vol. 74 (1991), pp. 1320.

[4]R. Christoferson and P.K. Davis: J. Am. Ceram. Soc. Vol. 75 (1992), pp. 563.

[5] A.E. McHall and R.S. Roth: J. Am. Ceram. Soc. Vol. 66 (1983), pp. C18.

[6]S.X. Zhang, J.B. Li, h.Z. Zhai and J.H. Dai: Ceram. Inter. Vol. 28 (2002), pp. 407.

[7] C.L. Huang and M.H. Weng: Res. Bull. Vol. 35 (2000), pp. 1881.

[8] D.J. Kim, J.W. Hahn, G.P. Han, S.S. Lee and T.G. Choy: J. Am. Ceram. Soc. Vol. 83 (2000), pp.

1010.

[9] C.L. Huang, M.H. Weng and H.L. Chen: mater. Chem. ＆ phys. Vol. 71 (2001), pp. 17

[10]M. Takata and K. Kageyama: J. Am. Ceram. Soc. Vol. 72 (1989), pp. 1955.

[11]D.N. Iddles, A.J. Bell and A.J. Moulson: J. Mat. Sci. Vol. 27 (1992), pp. 6303.

High-Performance Ceramics III

10.4028/https://www.360docs.net/doc/3217821458.html,/KEM.280-283

Dielectric Properties of Zirconium Tin Titanate with Additives of ZnO, CuO, MnCO3 and Bi2O3 10.4028/https://www.360docs.net/doc/3217821458.html,/KEM.280-283.91