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Microwave dielectric properties of low temperature co-fired glass–ceramic based on B2O3–La2O3–MgO glass with La(Mg0.5Ti0.5)O3 ceramics
Available online at www.sciencedirect.com
Materials Letters 62 (2008) 611 – 614 www.elsevier.com/locate/matlet
Microwave dielectric properties of low temperature co-fired glass–ceramic based on B2O3–La2O3–MgO glass with La(Mg0.5Ti0.5)O3 ceramics Huixing Lin ⁎, Aimin Yang, Lan Luo, Wei Chen Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai, 200050, PR China Received 18 October 2005; accepted 8 June 2007 Available online 16 June 2007
Abstract Glass–ceramic materials based on B2O3–La2O3–MgO glass with La(Mg0.5Ti0.5)O3 ceramics were fabricated. The sintering behavior and microwave dielectric properties of glass–ceramic were investigated. With the increase of sintering temperature, the εr value of glass–ceramic decreased, while the Q × f value increased obviously and the τf value only increased slightly. Glass–ceramic sintered at 850 °C had an excellent microwave dielectric property: εr = 11.8, Q × f = 14,700 GHz and τf = 7.4 ppm/°C. © 2007 Elsevier B.V. All rights reserved. Keywords: Glass–ceramic; Microwave dielectric property; La(Mg0.5Ti0.5)O3; LTCC
1. Introduction
2. Experimental
Due to the necessity for miniaturization of microwave divices to reduce the size of wireless communication system, low temperature co-fired ceramics (LTCC) have recently been widely investigated [1–6]. The melting temperature of co-fired silver electrodes in a multi-layer device limits the sintering temperature to 900 °C. However, most of the commercial microwave dielectric ceramics usually need high sintering temperature [7–9]. To solve this problem, low melting glass frits are usually mixed with ceramic materials to reduce the sintering temperature to below 900 °C [3,4,6,10]. La (Mg0.5Ti0.5)O3 ceramics have suitable dielectric constant and quality factors for application of dielectric resonators and filters [11]. It exhibits dielectric constant of 28, Q × f of 63,100 GHz and negative τf of − 79 ppm/°C. However, La(Mg0.5Ti0.5)O3 ceramics required very high sintering temperature (1630 °C). For obtaining the LTCC glass–ceramic, in this paper the glasses B2O3–La2O3–MgO were fabricated to be mixed with LMT ceramics. The sintering characteristic and microwave dielectric properties of the glass–ceramic under different sintering condition were investigated.
Microwave ceramic La(Mg0.5Ti0.5)O3 (LMT) were prepared using the conventional mixed oxide method. High purity powders La2O3, MgO and TiO2 with a molar ratio of nominal composition LMT were mixed and calcined at 1450°C for 3 h. Reactive sintering glass composition BLM containing B2O3 60%, La2O3 12% and MgO 28% (in mol%) were prepared by melting in an platinum crucible at 1200 °C for 1 h. Mixtures of calcined
⁎ Corresponding author. Tel.: +86 21 52414233; fax: +86 21 52413903. E-mail address: [email protected] (H. Lin). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.06.020
Fig. 1. The DTA curve of BLM glass at 10 °C/min heating rate.
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H. Lin et al. / Materials Letters 62 (2008) 611–614
The bulk densities were measured by the Archimedes method. Differential thermal analysis (DTA) was carried out for powdered glass specimens with NETZSCH STA429C analyzer at 10 °C/min heating rate. The crystalline phases of the sintered samples were identified using a Rigaku RAX-10 diffractometer with a conventional Cu Kα radiation. Microstructure observations of the natural surface of sintered glass– ceramic were studied by using Scanning Electron Microscope (JSM-6360LV, JEOL, Japan). The method developed by Hakki and Coleman [12] was used to measure the microwave dielectric properties of the pellets which were polished into disks 8 mm in diameter and 4 mm in height. The measuring frequency ranges from 6 to 10 GHz. All microwave measurements were used with the TE011 mode of an Agilent E8363A PNA series network analyzer. The temperature coefficient of resonant frequency was measured in the temperature range of − 25–85 °C. Fig. 2. The XRD of the glass–ceramic with the different sintering temperature.
3. Results and discussion
ceramic LMT (6.082 g/cm3) (50 wt.%) with reactive BLM glass (3.453 g/cm3) (50 wt.%) were firstly ball-milled for 24 h. The milled powders were then dried at 120 °C and granulated with PVA. After the powders were preformed using cylindrical mold of 16 mm diameter, they were pressed at 2000 kg/cm2 with coldisostatic pressing. The pellets were sintered at 850–1000 °C for 2 h in air with a heating rate of 5 °C /min.
Fig. 1 shows the DTA curve of BLM glass at 10 °C /min heating rate. The glass transition temperature (Tg) of BLM glass was 665 °C. The BLM glass had three crystallization peaks: 787 °C, 851 °C and 976 °C, respectively. The BLM glass also showed the melting point at 1045 °C. This result showed that BLM glass with low Tg, Tp, and Tm was suitable for LTCC application. Fig. 2 shows the XRD of the glass–ceramic with the different sintering temperature. There had two initial phases such as glass and
Fig. 3. The SEM images of glass–ceramic after sintering at different temperature. (a) 850 °C, (b) 900 °C, (c) 950 °C and (d) 1000 °C.
H. Lin et al. / Materials Letters 62 (2008) 611–614
613
Fig. 4. The density of glass–ceramic as a function of sintering temperature.
Fig. 6. The temperature coefficient of resonant frequency τf of glass–ceramic sintered at different temperature for 2 h.
ceramic phases at room temperature, but as the samples underwent sintering, different phases were formed. At 850 °C, various phases existed including ceramic phase LMT, LaBO3 (JCPDS no. 12-0736), TiO2 and a small amount of amorphous (glassy) phase which was not yet crystallized. With the increase of sintering temperature, the ceramic phase and amorphous phase decreased. The sample sintered at 1050 °C deformed because a large amount of liquid phase appeared at 1050 °C which was in accord with the DTA of BLM glass. The SEM images of glass–ceramic after sintering at different temperature were shown in Fig. 3. As the sintering temperature increased, the reaction between glass and ceramic increased, and grains became larger at the same time. Fig. 4 shows the density of glass–ceramic as a function of sintering temperature. The density of glass–ceramic decreased with the increase of sintering temperature. With the increase of sintering temperature, the interaction between BLM glass and LMT ceramics increased. From the result of XRD, BLM glass and LMT ceramics changed to LaBO3 and TiO2 phase. The density of LaBO3 phase (5.304 g/cm3) and TiO2 phase (4.251 g/cm3) is less than that of LMT phase (6.082 g/cm3). Another reason about the decrease of the density of glass–ceramic may be that the porosity of glass–ceramic increased with the increase of sintering temperature as shown in Fig. 3. Fig. 5 illustrates the dielectric constants εr and Q × f value of glass– ceramic sintered at different temperatures for 2 h. The relationship
between εr values and sintering temperatures reveals the same trend as that between densities and sintering temperatures. According to XRD patterns, the La(Mg0.5Ti0.5)O3 content decreased and the LaBO3 phase increased with the increase of sintering temperature. LaBO3 had lower εr than La(Mg0.5Ti0.5)O3 [13] and the LMT was minor phase, this maybe result in the slight decrease of εr values of glass–ceramic. The dielectric constant is mainly controlled by the porosity of glass– ceramic. Fig. 3 shows that the porosity increased distinctly when sintering temperatures were higher than 925 °C. The εr value of glass– ceramic decreased slightly with the increase of sintering temperature from 850 to 925 °C and then decreased distinctly. The variable trend of Q × f values of glass–ceramic was different from that of the relative dielectric constant. The Q × f values of glass–ceramic increased with the increase of sintering temperature. The main reason was the decrease of glass content with the increase of sintering temperature. The network formers contained in the remaining glass can profoundly absorb the microwave power at high frequencies, which caused the degradation of the Q × f values of glass–ceramic [14]. Fig. 6 shows the temperature coefficient of resonant frequency τf of glass–ceramic sintered at different temperature for 2 h. The τf values of glass–ceramic slightly increased from 7.4 to 15.7 ppm/ °C with the increase of sintering temperature from 850 to 1000 °C. This attributed to the decrease of LMT phase and the increase of LaBO3 and TiO2 phase. The τf value of LMT, LaBO3 and TiO2 phase was-79, 670 and 450 ppm/ °C, respectively [11,15].
4. Conclusions
Fig. 5. The permittivity εr and Q × f of glass–ceramic sintered at different temperature for 2 h.
Glass–ceramic materials based on B2O3–La2O3–MgO glass with La(Mg0.5Ti0.5)O3 ceramics were fabricated at a sintering temperature of b 1000 °C. In the sintering process, the reaction between LMT ceramics and BLM glass occurred, and LaBO3 and TiO2 phase appeared. With the increase of sintering temperature, the densities and εr value of glass–ceramic decreased, but the Q × f value increased. And the τf value slightly increased with the increase of sintering temperature. Glass–ceramic sintered at 850 °C had an excellent microwave dielectric property: εr = 11.8, Q × f = 14700 GHz and τf = 7.4 ppm/ °C. The results suggested that glass–ceramic in this experiment was an excellent LTCC microwave dielectric material.
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H. Lin et al. / Materials Letters 62 (2008) 611–614
References [1] W. Wersing, Curr. Opin. Solid State Mater. Sci. 5 (1996) 715. [2] D.L. Sr Wilcox, R.F. Huang, S.X. Dai, Am. Ceram. Soc. Ceram. Trans. 97 (1999) 201. [3] B.H. Jung, S.J. Hwang, H.S. Kim, J. Eur. Ceram. Soc. 25 (2005) 3187. [4] C.S. Chen, C.C. Chou, C.S. Chen, I.N. Lin, J. Eur. Ceram. Soc. 24 (2004) 1795. [5] M. Valant, D. Suvorov, Mater. Chem. Phys. 79 (2003) 104. [6] C.C. Cheng, T.E. Hsieh, I.N. Lin, J. Eur. Ceram. Soc. 23 (2003) 2553. [7] P.H. Sun, T. Nakamura, Y.J. Shan, Y. Inaguma, M. Itoh, T. Kitamura, Jpn. J. Appl. Phys. 37 (1998) 5625.
[8] C.L. Huang, R.Y. Yang, M.H. Weng, Jpn. Soc. Appl. Phys. 39 (2000) 6608. [9] S.Y. Cho, I.T. Kim, K.S. Hong, Jpn. J. Appl. Phys. 37 (1998) 593. [10] O. Dernovsek, A. Naeini, G. Preu, W. Wersing, M. Eberstein, W.A. Schiller, J. Eur. Ceram. Soc. 21 (2001) 1693. [11] D. Lee, S. Yoon, J. Mater. Sci. Lett. 19 (2000) 131. [12] B.W. Hakki, P.D. Coleman, IRE Trans. Microwave Theor. Tech. 8 (1960) 402. [13] C.H. Lu, C.C. Tsai, Mater. Sci. Eng., B 55 (1998) 95. [14] S.H. Wang, H.P. Zhou, J. Mater. Sci. Eng. B 99 (2003) 597. [15] O. Dernovsek, A. Naeini, G. Preu, W. Wersing, M. Eberstein, W.A. Schiller, J. Eur. Ceram. Soc. 21 (2001) 1693.
Materials Letters 62 (2008) 611 – 614 www.elsevier.com/locate/matlet
Microwave dielectric properties of low temperature co-fired glass–ceramic based on B2O3–La2O3–MgO glass with La(Mg0.5Ti0.5)O3 ceramics Huixing Lin ⁎, Aimin Yang, Lan Luo, Wei Chen Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai, 200050, PR China Received 18 October 2005; accepted 8 June 2007 Available online 16 June 2007
Abstract Glass–ceramic materials based on B2O3–La2O3–MgO glass with La(Mg0.5Ti0.5)O3 ceramics were fabricated. The sintering behavior and microwave dielectric properties of glass–ceramic were investigated. With the increase of sintering temperature, the εr value of glass–ceramic decreased, while the Q × f value increased obviously and the τf value only increased slightly. Glass–ceramic sintered at 850 °C had an excellent microwave dielectric property: εr = 11.8, Q × f = 14,700 GHz and τf = 7.4 ppm/°C. © 2007 Elsevier B.V. All rights reserved. Keywords: Glass–ceramic; Microwave dielectric property; La(Mg0.5Ti0.5)O3; LTCC
1. Introduction
2. Experimental
Due to the necessity for miniaturization of microwave divices to reduce the size of wireless communication system, low temperature co-fired ceramics (LTCC) have recently been widely investigated [1–6]. The melting temperature of co-fired silver electrodes in a multi-layer device limits the sintering temperature to 900 °C. However, most of the commercial microwave dielectric ceramics usually need high sintering temperature [7–9]. To solve this problem, low melting glass frits are usually mixed with ceramic materials to reduce the sintering temperature to below 900 °C [3,4,6,10]. La (Mg0.5Ti0.5)O3 ceramics have suitable dielectric constant and quality factors for application of dielectric resonators and filters [11]. It exhibits dielectric constant of 28, Q × f of 63,100 GHz and negative τf of − 79 ppm/°C. However, La(Mg0.5Ti0.5)O3 ceramics required very high sintering temperature (1630 °C). For obtaining the LTCC glass–ceramic, in this paper the glasses B2O3–La2O3–MgO were fabricated to be mixed with LMT ceramics. The sintering characteristic and microwave dielectric properties of the glass–ceramic under different sintering condition were investigated.
Microwave ceramic La(Mg0.5Ti0.5)O3 (LMT) were prepared using the conventional mixed oxide method. High purity powders La2O3, MgO and TiO2 with a molar ratio of nominal composition LMT were mixed and calcined at 1450°C for 3 h. Reactive sintering glass composition BLM containing B2O3 60%, La2O3 12% and MgO 28% (in mol%) were prepared by melting in an platinum crucible at 1200 °C for 1 h. Mixtures of calcined
⁎ Corresponding author. Tel.: +86 21 52414233; fax: +86 21 52413903. E-mail address: [email protected] (H. Lin). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.06.020
Fig. 1. The DTA curve of BLM glass at 10 °C/min heating rate.
612
H. Lin et al. / Materials Letters 62 (2008) 611–614
The bulk densities were measured by the Archimedes method. Differential thermal analysis (DTA) was carried out for powdered glass specimens with NETZSCH STA429C analyzer at 10 °C/min heating rate. The crystalline phases of the sintered samples were identified using a Rigaku RAX-10 diffractometer with a conventional Cu Kα radiation. Microstructure observations of the natural surface of sintered glass– ceramic were studied by using Scanning Electron Microscope (JSM-6360LV, JEOL, Japan). The method developed by Hakki and Coleman [12] was used to measure the microwave dielectric properties of the pellets which were polished into disks 8 mm in diameter and 4 mm in height. The measuring frequency ranges from 6 to 10 GHz. All microwave measurements were used with the TE011 mode of an Agilent E8363A PNA series network analyzer. The temperature coefficient of resonant frequency was measured in the temperature range of − 25–85 °C. Fig. 2. The XRD of the glass–ceramic with the different sintering temperature.
3. Results and discussion
ceramic LMT (6.082 g/cm3) (50 wt.%) with reactive BLM glass (3.453 g/cm3) (50 wt.%) were firstly ball-milled for 24 h. The milled powders were then dried at 120 °C and granulated with PVA. After the powders were preformed using cylindrical mold of 16 mm diameter, they were pressed at 2000 kg/cm2 with coldisostatic pressing. The pellets were sintered at 850–1000 °C for 2 h in air with a heating rate of 5 °C /min.
Fig. 1 shows the DTA curve of BLM glass at 10 °C /min heating rate. The glass transition temperature (Tg) of BLM glass was 665 °C. The BLM glass had three crystallization peaks: 787 °C, 851 °C and 976 °C, respectively. The BLM glass also showed the melting point at 1045 °C. This result showed that BLM glass with low Tg, Tp, and Tm was suitable for LTCC application. Fig. 2 shows the XRD of the glass–ceramic with the different sintering temperature. There had two initial phases such as glass and
Fig. 3. The SEM images of glass–ceramic after sintering at different temperature. (a) 850 °C, (b) 900 °C, (c) 950 °C and (d) 1000 °C.
H. Lin et al. / Materials Letters 62 (2008) 611–614
613
Fig. 4. The density of glass–ceramic as a function of sintering temperature.
Fig. 6. The temperature coefficient of resonant frequency τf of glass–ceramic sintered at different temperature for 2 h.
ceramic phases at room temperature, but as the samples underwent sintering, different phases were formed. At 850 °C, various phases existed including ceramic phase LMT, LaBO3 (JCPDS no. 12-0736), TiO2 and a small amount of amorphous (glassy) phase which was not yet crystallized. With the increase of sintering temperature, the ceramic phase and amorphous phase decreased. The sample sintered at 1050 °C deformed because a large amount of liquid phase appeared at 1050 °C which was in accord with the DTA of BLM glass. The SEM images of glass–ceramic after sintering at different temperature were shown in Fig. 3. As the sintering temperature increased, the reaction between glass and ceramic increased, and grains became larger at the same time. Fig. 4 shows the density of glass–ceramic as a function of sintering temperature. The density of glass–ceramic decreased with the increase of sintering temperature. With the increase of sintering temperature, the interaction between BLM glass and LMT ceramics increased. From the result of XRD, BLM glass and LMT ceramics changed to LaBO3 and TiO2 phase. The density of LaBO3 phase (5.304 g/cm3) and TiO2 phase (4.251 g/cm3) is less than that of LMT phase (6.082 g/cm3). Another reason about the decrease of the density of glass–ceramic may be that the porosity of glass–ceramic increased with the increase of sintering temperature as shown in Fig. 3. Fig. 5 illustrates the dielectric constants εr and Q × f value of glass– ceramic sintered at different temperatures for 2 h. The relationship
between εr values and sintering temperatures reveals the same trend as that between densities and sintering temperatures. According to XRD patterns, the La(Mg0.5Ti0.5)O3 content decreased and the LaBO3 phase increased with the increase of sintering temperature. LaBO3 had lower εr than La(Mg0.5Ti0.5)O3 [13] and the LMT was minor phase, this maybe result in the slight decrease of εr values of glass–ceramic. The dielectric constant is mainly controlled by the porosity of glass– ceramic. Fig. 3 shows that the porosity increased distinctly when sintering temperatures were higher than 925 °C. The εr value of glass– ceramic decreased slightly with the increase of sintering temperature from 850 to 925 °C and then decreased distinctly. The variable trend of Q × f values of glass–ceramic was different from that of the relative dielectric constant. The Q × f values of glass–ceramic increased with the increase of sintering temperature. The main reason was the decrease of glass content with the increase of sintering temperature. The network formers contained in the remaining glass can profoundly absorb the microwave power at high frequencies, which caused the degradation of the Q × f values of glass–ceramic [14]. Fig. 6 shows the temperature coefficient of resonant frequency τf of glass–ceramic sintered at different temperature for 2 h. The τf values of glass–ceramic slightly increased from 7.4 to 15.7 ppm/ °C with the increase of sintering temperature from 850 to 1000 °C. This attributed to the decrease of LMT phase and the increase of LaBO3 and TiO2 phase. The τf value of LMT, LaBO3 and TiO2 phase was-79, 670 and 450 ppm/ °C, respectively [11,15].
4. Conclusions
Fig. 5. The permittivity εr and Q × f of glass–ceramic sintered at different temperature for 2 h.
Glass–ceramic materials based on B2O3–La2O3–MgO glass with La(Mg0.5Ti0.5)O3 ceramics were fabricated at a sintering temperature of b 1000 °C. In the sintering process, the reaction between LMT ceramics and BLM glass occurred, and LaBO3 and TiO2 phase appeared. With the increase of sintering temperature, the densities and εr value of glass–ceramic decreased, but the Q × f value increased. And the τf value slightly increased with the increase of sintering temperature. Glass–ceramic sintered at 850 °C had an excellent microwave dielectric property: εr = 11.8, Q × f = 14700 GHz and τf = 7.4 ppm/ °C. The results suggested that glass–ceramic in this experiment was an excellent LTCC microwave dielectric material.
614
H. Lin et al. / Materials Letters 62 (2008) 611–614
References [1] W. Wersing, Curr. Opin. Solid State Mater. Sci. 5 (1996) 715. [2] D.L. Sr Wilcox, R.F. Huang, S.X. Dai, Am. Ceram. Soc. Ceram. Trans. 97 (1999) 201. [3] B.H. Jung, S.J. Hwang, H.S. Kim, J. Eur. Ceram. Soc. 25 (2005) 3187. [4] C.S. Chen, C.C. Chou, C.S. Chen, I.N. Lin, J. Eur. Ceram. Soc. 24 (2004) 1795. [5] M. Valant, D. Suvorov, Mater. Chem. Phys. 79 (2003) 104. [6] C.C. Cheng, T.E. Hsieh, I.N. Lin, J. Eur. Ceram. Soc. 23 (2003) 2553. [7] P.H. Sun, T. Nakamura, Y.J. Shan, Y. Inaguma, M. Itoh, T. Kitamura, Jpn. J. Appl. Phys. 37 (1998) 5625.
[8] C.L. Huang, R.Y. Yang, M.H. Weng, Jpn. Soc. Appl. Phys. 39 (2000) 6608. [9] S.Y. Cho, I.T. Kim, K.S. Hong, Jpn. J. Appl. Phys. 37 (1998) 593. [10] O. Dernovsek, A. Naeini, G. Preu, W. Wersing, M. Eberstein, W.A. Schiller, J. Eur. Ceram. Soc. 21 (2001) 1693. [11] D. Lee, S. Yoon, J. Mater. Sci. Lett. 19 (2000) 131. [12] B.W. Hakki, P.D. Coleman, IRE Trans. Microwave Theor. Tech. 8 (1960) 402. [13] C.H. Lu, C.C. Tsai, Mater. Sci. Eng., B 55 (1998) 95. [14] S.H. Wang, H.P. Zhou, J. Mater. Sci. Eng. B 99 (2003) 597. [15] O. Dernovsek, A. Naeini, G. Preu, W. Wersing, M. Eberstein, W.A. Schiller, J. Eur. Ceram. Soc. 21 (2001) 1693.