Elsevier

Ceramics International

Volume 44, Issue 5, 1 April 2018, Pages 5010-5016
Ceramics International

Co2O3 substitution effects on the structure and microwave dielectric properties of low-firing (Zn0.9Mg0.1)TiO3 ceramics

https://doi.org/10.1016/j.ceramint.2017.12.097Get rights and content

Abstract

Low-firing (Zn0.9Mg0.1)1−xCoxTiO3 (x = 0.02–0.10) (ZMCxT) microwave dielectric ceramics with high temperature stability were synthesized via conventional solid-state reaction. The influences of Co2O3 substitution on the phase composition, microstructure and microwave dielectric properties of ZMCxT ceramics were discussed. Rietveld refinement results show the coexistence of ZnTiO3 and ZnB2O4 phases at x = 0.02–0.10. (Zn0.9Mg0.1)1−xCoxTiO3 ceramic with x = 0.06 (ZMC0.06T) obtains the best combination microwave dielectric properties of: εr = 21.58, Q × f = 53,948 GHz, τf = − 54.38 ppm/°C. For expanding its application in LTCC field, 3 wt% ZnO-B2O3-SiO2 (ZBS) and 9 wt% TiO2 was added into ZMC0.06T ceramic, great microwave dielectric properties were achieved at 900 °C for 4 h: εr = 26.03, Q × f = 34,830 GHz, τf = − 4 ppm/°C, making the composite ceramic a promising candidate for LTCC industry.

Introduction

High frequency passive components such as microwave dielectric resonators and antenna have been rapidly developed for cellular phones and global positioning systems in the past decades. Low temperature co-fired ceramics (LTCC) technology has been playing a significant role in this field. Requirements for these dielectric components must combine excellent dielectric properties such as a moderate dielectric constant (εr), a low dielectric loss of the quality factor (Q × f) and a near-zero temperature coefficient of resonant frequency (τf), which allows the components to operate normally under a wide temperature range [1], [2], [3].

ZnO-TiO2 based ceramics have been one favorite research for years because of their excellent microwave dielectric properties. In their phase diagram reported by Yang and Swisher [4], three phases are known to exist: Zn2TiO4 (cubic), ZnTiO3 (hexagonal), and Zn2Ti3O8 (cubic). Zn2TiO4 can be easily prepared by the conventional solid-state reaction with mole ration of ZnO: TiO2 = 2:1, possessing microwave dielectric properties of εr = 21, Q × f = 20,000 GHz, τf = − 60 ppm/°C) [5], [6], [7]. However, its poor Q × f and τf value limits its practical application. Zn3Ti2O8 has the same cubic structure of Zn2TiO4. However, it transforms to ZnTiO3 at about 820 °C [5], [8], which has a negative impact on the properties. ZnTiO3 has a multilayer structure with excellent microwave dielectric properties (εr = 19, Q × f = 30,000 GHz, τf = − 55 ppm/°C), which decomposes into Zn2TiO4 and TiO2 when heating temperature above 945 ℃ [5], [9], [10], and it is possible for cofiring with Ag electrode (not exceed melting point of Ag, about 951 °C), which makes ZnTiO3 promising for LTCC application. Nevertheless, the Q×f value of ZnTiO3 is still not good. Our previous study shows a great enhancement in Q × f value with small amount of Mg2+ addition: εr = 20.53, Q × f = 61,630 GHz, τf = − 76 ppm/°C for (Zn0.9Mg0.1)TiO3 [11], but the τf value still too poor to be used in LTCC field.

Theoretically, since a close ionic radius of Co2+ (0.745 Å) with Zn2+ (0.74 Å) and Mg2+ (0.72 Å) at the same coordinate number [12], CoTiO3 has the same crystal structure of ZnTiO3. And in our previous work of Zn-Nb-Ti system, we found the substitution of Co2+ in Zn site has an improvement of the negative τf value and still maintain great microwave dielectric properties [13]. Thus, Co2O3 was considered to add into Zn0.9Mg0.1TiO3. And for improving its application in LTCC field, ZnO-B2O3-SiO2 (ZBS) glass was performed as a sintering aid to decrease the sintering temperature. The influence of Co2+ substitution on the crystal structure, microstructures and microwave dielectric properties of (Zn0.9Mg0.1)1−xCoxTiO3 ceramics have been investigated in detail.

Section snippets

Experimental

Samples of (Zn0.9Mg0.1)1−xCoxTiO3 (ZMCxT) were prepared with high purity materials: ZnO (Liuzhou at the Zinc Product Co., Ltd., Liuzhou, China, 99.7%), MgO (Industrial development zone, Mulan Town, Xindu, Chengdu, China, 98.0%), Co2O3 (Industrial development zone, Mulan Town, Xindu, Chengdu, China, 99.0%), TiO2 (Xiantao Zhongxing Electronic Materials Co., Ltd, Hubei, China, 99.9%). The starting materials were mixed together and then ball-milled in a nylon jar with zirconia balls for 24 h in the

Results and discussion

The X-ray diffraction patterns of ZMCxT + 3 wt% ZBS ceramics sintered at 900 °C for 4 h are displayed in Fig. 1(a). Phase compositions under different x values were indexed as ZnTiO3 phase (JCPDS # 26-1500, Hexagonal, R-3 (148)) and ZnB2O4 phase (JCPDS # 39-1126, Cubic, Im-3m (229)), no additional peaks corresponding to other phases were found. According to the phase diagram of ZnO-B2O3-SiO2, there does exist a formation of ZnB2O4 phase [15]. Rietveld refinement was applied to obtain important

Conclusion

The present work mainly discusses the influences of Co2+ substitution on the crystal structure and microwave dielectric properties of (Zn0.9Mg0.1)TiO3 ceramics. ZnTiO3 and ZnB2O4 phases coexist at x = 0.02 ~ 0.10, cell volumes decrease at 0.04 and 0.10 are mainly attributed to the bond length decrease of Zn/Mg/Co-O1(1), Zn/Mg/Co-O1(2), Ti-O1(1) and structural stability. The decrease of εr value is attributed to the decreased dielectric polarizability and the lower εr values of ZnB2O4 phase and

References (30)

  • F. Lichtenberg et al.

    Synthesis, structural, magnetic and transport properties of layered perovskite-related titanates, niobates and tantalates of the type AnBnO3n+2, A′Ak−1BkO3k+1 and AmBm−1O3m

    Prog. Solid State Chem.

    (2008)
  • J.R. Kim et al.

    Low-temperature sintering and microwave dielectric properties of Ba5Nb4O15 with ZnB2O4 glass

    J. Eur. Ceram. Soc.

    (2006)
  • W.B. Li et al.

    Structure, Raman spectra, far-infrared spectra and microwave dielectric properties of temperature independent CeVO4–TiO2 composite ceramics

    J. Alloy. Compd.

    (2017)
  • M. Sebastian et al.

    Low loss dielectric materials for LTCC applications: a review

    Int. Mater. Rev.

    (2008)
  • D. Zhou et al.

    High permittivity, low loss microwave dielectrics suitable for 5G resonator and low temperature co-fired ceramic architecture

    J. Mater. Chem. C

    (2017)
  • Cited by (15)

    • Synthesis of a low-firing BaSi<inf>2</inf>O<inf>5</inf> microwave dielectric ceramics with low dielectric constant

      2022, Ceramics International
      Citation Excerpt :

      Although the use of additives may harm the microwave dielectric properties of ceramics, they can potentially be used in commercial applications. In the previous studies [19–23], the addition of Li2O–B2O3–SiO2 (LBS) glass and ZnO–B2O3–SiO2 successfully promoted sintering at low temperatures. Duan et al. [24] showed that LBS glass can effectively reduce the sintering temperature of Ba–Zn–Ti dielectric materials.

    • Structure, microwave dielectric properties, and THz spectrum of Co<inf>0.5</inf>Sn<inf>0.5</inf>TaO<inf>4</inf> ceramics

      2022, Materials Letters
      Citation Excerpt :

      It is reasonable to guess there is an abnormal growth of grain occurring after 1300 °C. The distortion (△) of the oxygen octahedron is responsible for the vibration restoring force [13]. In this study, the △ value of [M2O6] octahedron shows an inseparable relationship with the TCF value.

    View all citing articles on Scopus
    View full text