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Sintering characteristic, structure, microwave dielectric properties, and compatibility with Ag of novel 3MgO-B2O3-xwt% BaCu(B2O5)-ywt% H3BO3 ceramics Sintering characteristic, structure, microwave dielectric properties, and compatibility with Ag...
Wang, Haiquan; Li, Shixuan; Wang, Kangguo; Wang, Xi; Zhang, Hailin; Wu, You; Chen, Xiuli; Zhou, Huanfu
2022-04-03 00:00:00
JOURNAL OF ASIAN CERAMIC SOCIETIES 2022, VOL. 10, NO. 2, 346–355 https://doi.org/10.1080/21870764.2022.2053277 FULL LENGTH ARTICLE Sintering characteristic, structure, microwave dielectric properties, and compatibility with Ag of novel 3MgO-B O -xwt% BaCu(B O )-ywt% H BO 2 3 2 5 3 3 ceramics a,b a a a a a a Haiquan Wang , Shixuan Li , Kangguo Wang , Xi Wang , Hailin Zhang , You Wu , Xiuli Chen and Huanfu Zhou Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Materials in Guangxi, Key Laboratory of Nonferrous Materials and New Processing Technology, Ministry of Education, School of Materials Science and Engineering, Guilin University of Technology, Guilin, Guangxi, China; College of Mechanical and Electrical Engineering, Guangdong University of Petrochemical Technology, Maoming, Guangdong Province, China ABSTRACT ARTICLE HISTORY Received 8 November 2021 In this study, 3MgO-B O -xwt%BaCu(B O ) (BCB)-ywt%H BO (2 ≤ x ≤ 8, 0 ≤ y ≤ 20) ceramics 2 3 2 5 3 3 Accepted 10 March 2022 were sintered at the optimum temperature to form Mg B O and MgO phases. The effects of H 3 2 6 3 BO and BCB on the product characteristics, phase transition, microstructure, and microwave KEYWORDS dielectric properties of 3MgO-B O ceramics were investigated. The intensities of diffraction 2 3 Ceramics; Mg B 3 2 peaks of two phases varied with changing the x and y values. After sintering at 950°C, the O ; H 6 3 ceramics with x = 6 and y = 15 achieved the excellent microwave properties with a ε of 6.72, BO ; BCB; microwave Q × f of 83,205 GHz and τ of – 65.05 ppm/°C. Besides, the ceramics with x = 8 and y = 5 sintered dielectric properties at 925°C also achieved good microwave dielectric properties with a ε of 6.64, Q × f of 78,173 GHz and τ of – 57.27 ppm/°C. The sintering temperatures of above both ceramics are well lower than the melting point of Ag, showing promising applications in low temperature cofired ceramic devices. In particular, these two ceramics can be used as the potential candidate materials for microwave ceramics for 5 G technology, provided that τ can be further optimized. 1. Introduction -10 wt%H BO -4 wt%BCB manufactured at 900°C 3 3 In recent years, LTCC technology is widely used in and 925°C also had excellent microwave dielectric microwave circuits manufacturing and has become properties. MgO-rich 3MgO-B O ceramics with 2 3 the research hot topic for passive component integra- good microwave properties have also been of tion [1–7]. In particular, with the emergence of 5 G interest to scholars. Dosler reported that Mg B O 3 2 6 large-scale antenna (Massive MIMO) technology, the ceramics with a grain size of 1000 μm could reach number of antennas will increase exponentially. The Q × f values up to more than 220,000 GHz [21]. Gu demand of filters for signal frequency selection and et al. [22] found that pure-phase Mg B O ceramic 3 2 6 processing will grow with the passage of time, thus could be obtained when the Mg/B molar ratio is the demand for low-temperature co-fired ceramics 1.2. An appropriate excess of MgO could increase (LTCC) will also increase significantly [8–13]. LTCC tech- its Q × f value, but it did not contribute to its nology requires the dielectrics to cofire with high con- densification. Kan et al. [23] found that an appro- ductivity material electrodes. Because of the low priate amount of B O doping could effectively 2 3 melting point of electrodes (e.g. Ag melting point: lower the sintering temperature of this ceramic 961°C, Al melting point: 660°C), microwave dielectric and improved the dielectric properties of MgO materials is desired to have low sintering temperatures compound. As x = 0.99, xMgO–(1-x)B O ceramic 2 3 [14–17]. sintered at 1,350°C for 4 hours had a Q × f value of In the MgO-B O system, Zhou et al. [18–20] 773,300 GHz. Appropriate ion substitution has 2 3 reported that the sintering temperatures of MgO- been reported to favor densification and dielectric xB O ceramics could be reduced by adding BCB. properties of ceramics. For example, Gu et al. [24] 2 3 MgO-2B O -4 wt%BCB ceramics manufactured at found that (Mg Ca ) B O ceramics manufac- 2 3 0.8 0.2 3 2 6 925°C have the excellent microwave properties, tured at 1,250°C showed microwave dielectric which is a candidate for LTCC components. Based properties of ε = 6.8, Q × f = 103,556 GHz, and on the above researches, they found that MgO-2B τ = – 34.5 ppm/°C. Furthermore, they [22] also O -40 wt%H BO -4 wt%BCB and MgO-2B O reported that the (Mg Sr ) B O ceramics 3 3 3 2 3 0.998 0.002 3 2 6 CONTACT Huanfu Zhou zhouhuanfu@163.com School of Materials Science and Engineering, Guilin University of Technology, Guilin 541004, China This article has been republished with minor changes. These changes do not impact the academic content of the article. © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of The Korean Ceramic Society and The Ceramic Society of Japan. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. JOURNAL OF ASIAN CERAMIC SOCIETIES 347 sintered at 1250°C had the excellent microwave microwave properties of ceramics with addition of properties of ε = 6.9, Q × f = 110,820 GHz, and BCB and H BO in 3MgO-B O needs to be further r 3 3 2 3 τ = – 32.4 ppm/°C. investigated. Though 3MgO-B O material system has high Q × f Figure 1 shows the ternary-phase diagrams of 2 3 value, it is manufactured at high-sintering tempera- 3MgO-B O -BCB-H BO systems. Based on this ternary- 2 3 3 3 tures, which not only hinder their incorporation with phase diagrams, a series of ceramics of 3MgO-B O -xwt 2 3 low melting electrode and polymer-based substrates, %BCB-ywt%H BO (where x = 2, 4, 6, 8; y = 0, 5, 10, 15, 3 3 but also lead to huge energy consumption and vola- 20) were designed and prepared by a conventional solid tile components evaporation. Su et al. [25] found that state reaction method. The sintering behavior, micro- 2+ 2+ Ni can be used as a substitute of Zn to optimize structure, microwave dielectric properties, and compat- the sintering behavior and microwave dielectric prop- ibility with Ag of ceramics are also reported in detail. erties of Zn B O ceramics. In addition, they [26] 3 2 6 reported that a mixture of Mg B O and Zn B O 3 2 6 3 2 6 2. Materials and methods was used to obtain ceramics with excellent dielectric properties at 950°C. Dou et al. [27] investigated that Mg B O ceramics were prepared by the solid state 3 2 6 the Mg B O ceramics with 35% lithium magnesium reaction method. The raw materials were MgO 3 2 6 borosilicate glass sintered at 950°C for 3 h obtained (>98.5%, Sinopharm Chemical Reagent Co., Ltd., the excellent microwave dielectric properties with ε Shanghai, China), H BO (>99%, Sinopharm Chemical r 3 3 = 6.5, Q × f = 21,000 GHz, τ = – 49.5 ppm/°C. Hu et al. Reagent Co., Ltd., Shanghai, China), CuO (>99%, [28] found that 55 wt% lithium magnesium zinc bor- Sinopharm Chemical Reagent Co., Ltd., Shanghai, osilicate glass addition could reduce the sintering China), and Ba(OH) · 8H O (>99%, Sinopharm 2 2 temperature of Mg B O ceramics to ~950°C and Chemical Reagent Co., Ltd, Shanghai, China). The 3 2 6 achieve the excellent microwave dielectric properties MgO was calcined at 800°C for 2 h to remove water with a ε of 6.8, Q × f of 50,000 GHz, and τ of – 64 ppm/ and impurities. Ba(OH) · 8H O was sieved. After weigh- r f 2 2 °C. Usually, materials (such as H BO , CuO, and V O ) ing, the raw materials were ball milled with anhydrous 3 3 2 5 with low melting point are often added to lower the ethanol as the medium for 4 h, then dried and sieved. sintering temperature for liquid-phase sintering to The mixtures were calcined at 800°C for 4 h. The cal- obtain dense sintered ceramics [29–33]. However, cined powders mixed with H BO and predetermined 3 3 the microwave properties of ceramics doped with amount of BCB were subjected to secondary ball low melting point materials are , usually, much dete- milling. 5wt% Polyvinyl alcohol (PVA) was added as riorated [16,33,34]. The addition of BCB with low the binder to the pellet. The powders were pressed melting temperature, good wettability, and micro- into cylindrical samples with a diameter of 10 mm and wave dielectric properties could contribute to the a height of ~5 mm under 200 MPa. The resulted sam- densification of Mg B O ceramics [35–37]. However, ples were sintered in air at 850°C ~ 1050°C for 4 h. 3 2 6 it is difficult to obtain pure Mg B O ceramics because An X-ray diffraction spectroscopy (Model X’Pert Pro, 3 2 6 high-temperature sintering will lead to the volatiliza- PANalytical, Almelo, Netherlands) was used for structure tion of B O [22]. Although some studies have been analysis of the specimens. The microstructure of the 2 3 reported, the relationship between structure and ceramic surfaces was observed with a scanning electron Figure 1. Ternary phase diagrams of 3MgO-B O -BCB-H BO systems. 2 3 3 3 348 H. WANG ET AL. Figure 2. XRD patterns of 3MgO-B O -xwt%BCB (x = 2, 4, 6, 8) ceramics sintered at optimum temperatures: (a) x = 2, 1050°C, (b) 2 3 x = 4, 1025°C, (c) x = 6, 975°C, (d) x = 8, 950°C. microscope (SEM, JSM6380-LV SEM, JEOL, Tokyo, Japan). homogeneous and denser as x value increased. The The bulk density of the sintered samples was measured average grain sizes of the ceramics are approximately by Archimedes method. Microwave dielectric properties 1.88 µm (x = 2, 1050°C), 2.07 µm (x = 4, 1025°C), were measured using TE01 δ dielectric resonator 1.53 µm (x = 6, 975°C) and 1.81 µm (x = 8, 950°C). In method and network analyzer (E5071C, Agilent Co., particular, 3MgO-B O -6 wt% BCB showed variable 2 3 CA, USA) over a frequency range of 300 kHz to 20 GHz grain growth and finer grains at 975°C. This indicates at room temperature. τ values were obtained over that the addition of appropriate BCB sintering aids can a temperature range of 25°C to 85°C as shown below. refine the grains. In addition, the sintering temperature of 3MgO-B O -xwt%BCB (x = 2, 4, 6, 8) ceramics gra- 2 3 f f T T 0 6 τ ¼ � 10 dually decreased with the increase of x value. A grain f ðT T Þ T 0 boundary melting phenomenon appeared in 3MgO-B where, f and f represent the resonant frequencies at O -8 wt%BCB, indicating the critical role played by BCB T T 0 3 85°C (T) and 25°C (T ), respectively. as a sintering aid. The variation curves of ρ, ε , Q × f and τ of 3MgO-B r f 2 O -xwt%BCB (x = 2, 4, 6, 8) ceramics at different sinter- 3. Results and discussion ing temperature are shown in Figure 4. As shown in Figure 4, the bulk density first increased slightly and Figure 2 shows the XRD patterns of 3MgO-B O -xwt% 2 3 then decreased with the increase of the sintering tem- BCB (x = 2, 4, 6, 8; y = 0) ceramics sintered at the perature. With changing the sintering temperature, the optimum temperature. As x increased from 2 to 8, variation of ε is consistent with that of bulk density. two major phases, indexed as Mg B O (JCPDS: 75– 3 2 6 r The higher the bulk density is, the higher the permit- 1807) and MgO, were detected. The diffraction peaks tivity is. As the x value increased from 2 to 8, the bulk of MgO slowly decreased and that of Mg B O gradu- 3 2 6 density increased but the value of ε decreased, which ally enhanced with the increase of x, which indicates may be attributed to the addition of BCB with a low ε that with the increase of BCB content, the decrease of (ε 7.4) [35]. sintering temperature and B O volatilization will 2 3 r ~ The change of Q × f with sintering temperature for induce the increase of Mg B O content and decrease 3 2 6 3MgO-B O -xwt%BCB (x = 2, 4, 6, 8) ceramics is similar of MgO content. 2 3 to that of bulk density, as shown in (Figure 4). The Q × f SEM images of 3MgO-B O -xwt%BCB (x = 2, 4, 6, 8) 2 3 is mainly affected by ceramic densification. Higher ceramics with optimum sintering temperature are illu- density leads to a lower porosity and lower losses. strated in Figure 3. Dense microstructure was A moderate particle size is associated with higher observed. The grains gradually became more JOURNAL OF ASIAN CERAMIC SOCIETIES 349 Figure 3. SEM image of 3MgO-B O -xwt%BCB (x = 2, 4, 6, 8) ceramics sintered at optimum temperatures: (a) x = 2, 1050°C, (b) 2 3 x = 4, 1025°C, (c) x = 6, 975°C, (d) x = 8, 950°C. Figure 4. Bulk densities and microwave dielectric properties (ε , Q × f and τ ) of the 3MgO-B O -xwt%BCB (x value ranges from 2 r f 2 3 to 8) ceramics at different sintering temperatures (S.T.). quality factors and lower grain boundary losses [38]. decreased the sintering temperature of ceramics but However, desired moderate particle size cannot be also resulted in denser ceramic, which are consistent obtained for ceramics at lower sintering temperatures. with the analysis of the SEM images, as shown in Figure The bulk density of samples first increased and then 3. The Q × f values of 3MgO-B O -xwt%BCB (x = 2, 4, 2 3 decreased with the increase of x, indicating that the 6, 8) ceramics initially increased to the maximum addition of appropriate amounts of BCB not only values and then decreased. The optimum sintering 350 H. WANG ET AL. Figure 6 shows the SEM pictures and grain size dis- tribution of 3MgO-B O -2 wt%BCB-ywt%H BO (y = 0, 5, 2 3 3 3 10, 15, and 20) ceramics sintered at their optimum temperatures. The average grain sizes of the ceramics were approximately 1.93 µm (y = 0), 1.64 µm (y = 5), 2.47 µm (y = 10), 1.9 µm (y = 15), and 2.03 µm (y = 20). In particular, the porosity of the ceramic samples became smaller with the increase of H BO . The comparison of 3 3 the grain size of ceramics without and with H BO 3 3 shows that H BO had an influence on the growth 3 3 behavior of this ceramics, indicating that the appropri- ate amount of H BO could promote the growth of 3 3 ceramics. The optimum sintering temperatures of cera- mics gradually decreased with the increase of y. The optimum sintering temperatures were 1050°C, 1025°C, 1000°C, 975°C, and 975°C for y = 0, 5, 10, 15, and 20, Figure 5. XRD patterns of 3MgO-B O -2 wt%BCB-ywt%H BO respectively. In particular, the sintering temperature of 2 3 3 3 (y = 0, 5, 10, 15, and 20) ceramics sintered at their optimum ceramics decreased to 975°C ceramics and the ceramics temperatures: (a) y = 0, 1050°C, (b) y = 5, 1025°C, (c) y = 10, achieved higher densities at y = 15. At the same time, 1000°C, (d) y = 15, 975°C, (e) y = 20, 975°C. the optimum sintering temperature could be reduced with the increase of H BO , thus effectively preventing 3 3 temperature gradually decreased as the x increased the volatilization of low melting point B O . In addition, 2 3 from 2 to 8. The optimum Q × f values increased from H BO compensated for the volatilized B O , thus allow- 3 3 2 3 73,674 GHz to 99,008 GHz. With further increase of BCB ing more complete growth of ceramics grains. content, the Q × f decreased to 75,222 GHz. The first (Figure 7) illustrates the bulk density of 3MgO-B O 2 3 increase and then decrease of Q × f can be ascribed to -2 wt%BCB-ywt%H BO (y = 0, 5, 10, 15, and 20) ceramics 3 3 the deterioration of quality factor of 3MgO-B O by the 2 3 as a function of the sintering temperature. Clearly, the addition of excess BCB. bulk density of ceramic first increased and then The 3MgO-B O -xwt% BCB (x = 2, 4, 6, 8) cera- 2 3 decreased with the increase of sintering temperature. mics showed good overall performance: ε = 6.64– r This phenomenon indicates that the ceramic was effec - 7.36, Q × f = 73,674–99,008 GHz, τ = – 73.01 to – f tively sintered denser initially with increasing the sinter- 59.38 ppm/°C. BCB addition could reduce the sinter- ing temperature. Further, temperature increase would ing temperature of 3MgO-B O ceramics from 2 3 cause over-sintering of ceramic and resulted in lower 1,050°C to 950°C. Notably, 3MgO-B O -4 wt%BCB 2 3 density. The bulk density of 3MgO-B O -2 wt%BCB- 2 3 ceramics sintered at 1,025°C for 4 h exhibited the ywt%H BO (y = 0, 5, 10, 15, 20) ceramics showed an 3 3 excellent microwave dielectric properties with a ε r overall increasing trend with the H BO content increase, 3 3 of 7.36, a Q × f of 99,008 GHz, and a τ of – 59.38 f which may be attributed to the decrease in porosity, as ppm/°C. The 3MgO-B O -8 wt%BCB ceramic sintered 2 3 shown in Figure 5. As y increased from 5 to 15, the bulk 3 3 at 950°C for 4 h also had the excellent microwave density rises from 3.017 g/cm to 3.128 g/cm , indicating properties with a ε of 6.64, a Q × f of 75,222 GHz, r that the addition of appropriate H BO could make the 3 3 and a τ of – 64.92 ppm/°C. f ceramic samples sinter more densely. However, with Figure 5 exhibits the room-temperature XRD pat- further increasing x value to 20, the bulk density reached terns of 3MgO-B O -2 wt%BCB-ywt%H BO (y = 0, 5, 2 3 3 3 the lowest at ρ of 3.04 g/cm , which is due to the over- 10, 15, and 20) ceramics sintered at their optimum sintering by addition of too much H BO . 3 3 temperatures. The constituent phases of the ceramics (Figure 7) demonstrates the change of τ for are Mg B O (PDF:038–1475) and MgO complex 3 2 6 3MgO-B O -2 wt%BCB-ywt%H BO (0 ≤ y ≤ 20) as 2 3 3 3 phases. However, the diffraction peaks of MgO a function of the sintering temperature. With the sin- decreased and that of Mg B O phase increased 3 2 6 tering temperature increase, τ first decreased and then with the increase of y, indicating that the increase in increased, which is consistent with the variation of H BO content not only decreased the sintering tem- 3 3 Q × f of ceramics. With the increase of y, the τ first perature but also compensated the boron content of increased and then decreased. When y = 20, the τ of 3MgO-B O ceramics. Therefore, the content of Mg 2 3 3 3MgO-B O -2 wt%BCB-20 wt%H BO ceramics 2 3 3 3 B O phase gradually increased, while the content of 2 6 remained stable in the range of – 60.2 to – 53.27 MgO phase gradually decreased, thereby directly ppm/°C, which allows the microwave electronic com- affecting the microwave dielectric properties of ponents maintaining temperature stability with 3MgO-B O -2 wt%BCB-ywt%H BO (y = 0, 5, 10, 15, 2 3 3 3 a nearly zero temperature coefficient of resonance and 20). frequency compared to other ceramics. JOURNAL OF ASIAN CERAMIC SOCIETIES 351 Figure 6. SEM images of 3MgO-B O -2 wt%BCB-ywt%H BO (y = 0, 5, 10, 15, and 20) ceramics sintered at their optimal 2 3 3 3 temperatures: (a) y = 0, 1050°C, (b) y = 5, 1025°C, (c) y = 10, 1000°C, (d) y = 15, 975°C, (e) y = 20, 975°C. (Figure 7) displays the ε of 3MgO-B O -2 wt%BCB- factors to affect the Q × f of microwave dielectric cera- r 2 3 ywt%H BO (y = 0, 5, 10, 15, and 20) as a function of the mics [41–43]. In (Figure 7), the Q × f of 3MgO-B O -2 wt 3 3 2 3 sintering temperature. The dielectric constants of cera- %BCB-ywt%H BO (y = 0, 5, 10, 15, 20) ceramics showed 3 3 mic materials are , generally, closely related to bulk a trend of increasing and then decreasing with the density, phase composition, and crystal structure increase of sintering temperature, which is similar to [39,40]. ε first increased to the maximum and then that of the bulk density and relative permittivity. From decreased with the increase of temperatures. As the analysis of phase structure and microstructure, the shown in Figure 6, the change in ε with temperature microstructure of 3MgO-B O -2 wt%BCB-ywt%H BO r 2 3 3 3 is similar to that of Q × f and bulk density. However, as (y = 0, 5, 10, 15, 20) ceramics is clearly relatively denser, the H BO content increased, the maximum values of and a second phase is present in addition to the main 3 3 dielectric constant for 3MgO-B O -2 wt%BCB-ywt%H phase 3MgO-B O . As y = 15, the ceramics possessed 2 3 3 2 3 BO ceramics increased first and then decreased (from relatively high Q × f and maximum density ρ of 3.128 g/ 6.95 to 7.05 and then to 6.67), which is similar to that of cm . With increasing the y to 20, the optimum sintering the bulk density of 3MgO-B O -2 wt%BCB-ywt%H BO temperature was 975°C. Combined with the XRD analy- 2 3 3 3 ceramics with sintering temperature. The dielectric con- sis, it is found that the Q × f of 3MgO-B O -2 wt%BCB- 2 3 stant increased with the increase of bulk density. As the ywt%H BO ceramic also reached the maximum value 3 3 bulk density of ceramic increased, the number of active of 113,645 GHz as y increased. The content of the main particles inside the ceramic was relatively high, and the phase of the ceramic increases as the content of dielectric constant increased and vice versa. the second-phase MgO in the crystal structure (Figure 7) shows the change of Q × f for 3MgO-B O decreases. 2 3 -2 wt%BCB-ywt%H BO (y = 0, 5, 10, 15, 20) ceramics vs Table 1 lists the optimum sintering temperature 3 3 the sintering temperature. In general, grain size, and microwave dielectric properties of 3MgO-B O - 2 3 porosity, second phase, and microcracks are the main xwt%BCB-ywt%H BO (where x = 2, 4, 6, and 8; y = 0, 3 3 352 H. WANG ET AL. Figure 7. Bulk density, ε , Q × f, and τ of 3MgO-B O -2 wt%BCB-ywt%H BO (0 ≤ y ≤ 20) ceramics sintered at optimal r f 2 3 3 3 temperatures as a function of y value. Table 1. Optimum sintering temperature and microwave dielectric properties of 3MgO-B O -xwt%BCB-ywt%H BO ceramics. 2 3 3 3 Compound S.T. ( C) Q × f (GHz) ε τ (ppm/°C) r f 3MgO-B O -2 wt%BCB 1050°C 73,674 6.95 –68.38 2 3 3MgO-B O -4 wt%BCB 1025°C 99,008 7.36 –59.38 2 3 3MgO-B O -6 wt%BCB 975°C 69,263 6.78 –73.01 2 3 3MgO-B O -8 wt%BCB 950°C 73,233 6.47 –68.52 2 3 3MgO-B O -2 wt%BCB-5 wt%H BO 1000°C 89,283 7.05 –61.53 2 3 3 3 3MgO-B O -4 wt%BCB-5 wt%H BO 975°C 69,055 6.92 –86.84 2 3 3 3 3MgO-B O -6 wt%BCB-5 wt%H BO 975°C 80,260 6.65 –57.93 2 3 3 3 3MgO-B O -8 wt%BCB-5 wt%H BO 925°C 78,173 6.64 –57.27 2 3 3 3 3MgO-B O -2 wt%BCB-10 wt%H BO 1025°C 77,819 7.04 –94.28 2 3 3 3 3MgO-B O -4 wt%BCB-10 wt%H BO 1000°C 72,409 6.93 –65.74 2 3 3 3 3MgO-B O -6 wt%BCB-10 wt%H BO 950°C 69,740 6.8 –86.99 2 3 3 3 3MgO-B O -8 wt%BCB-10 wt%H BO 950°C 58,689 6.95 –62.86 2 3 3 3 3MgO-B O -2 wt%BCB-15 wt%H BO 975°C 73,892 9.79 –66.80 2 3 3 3 3MgO-B O -4 wt%BCB-15 wt%H BO 975°C 74,136 6.95 –27.46 2 3 3 3 3MgO-B O -6 wt%BCB-15 wt%H BO 950°C 83,205 6.72 –65.05 2 3 3 3 3MgO-B O -8 wt%BCB-15 wt%H BO 900°C 63,711 6.51 –60.79 2 3 3 3 3MgO-B O -2 wt%BCB-20 wt%H BO 975°C 113,645 6.67 –53.19 2 3 3 3 3MgO-B O -4 wt%BCB-20 wt%H BO 975°C 81,667 6.55 –50.21 2 3 3 3 3MgO-B O -6 wt%BCB-20 wt%H BO 950°C 74,099 6.51 –66.98 2 3 3 3 3MgO-B O -8 wt%BCB-20 wt%H BO 950°C 78,401 6.53 –62.85 2 3 3 3 5, 10, 15, and 20) ceramics. The optimum sintering addition, the 3MgO-B O -2 wt%BCB-20 wt%H BO 2 3 3 3 temperature was decreased with the increase of BCB ceramic sintered at 975°C has the highest quality content when the value of y was constant. Notably, factor of 113,645 GHz, a ε of 6.67, and a τ of – 53.19 r f the sintering temperature of 3MgO-B O -8 wt%BCB ppm/°C. As observed by XRD, the increase in H BO 2 3 3 3 and 3MgO-B O -8 wt%BCB-5wt%H BO ceramics can content not only decreased the sintering temperature 2 3 3 3 be lowered to 925°C (<961°C, providing the possibility but also enhanced the intensity of the diffraction of cofiring with Ag). Both ceramics had high-quality peak for Mg B O , which indicates that Q × f 3 2 6 factors and low dielectric constants. The microwave increased with the increase of Mg B O content. 3 2 6 dielectric properties of 3MgO-B O -8 wt%BCB cera- However, when y = 20, the Q × f decreased with the 2 3 mics are as follows: ε = 6.47, Q × f = 73,233 GHz, τ increase of BCB, indicating that although BCB plays r f = – 68.52 ppm/°C. The microwave properties of the role as sintering aid, it also deteriorates the micro- 3MgO-B O -8 wt%BCB-5wt%H BO are as follows: ε wave dielectric properties of 3MgO-B O - 2 3 3 3 r 2 3 = 6.64, Q × f = 78,173 GHz, and τ = – 57.27 ppm/°C. In xwt%BCB-20 wt%H BO . f 3 3 JOURNAL OF ASIAN CERAMIC SOCIETIES 353 compensated the boron content of 3MgO-B O , mak- 2 3 ing 3MgO-B O crystal growth more complete and 2 3 denser. The highest Q × f of 113,645 GHz, ε of 6.67, τ r f of – 53.19 ppm/°C, and ρ of 3.04 g/cm of 3MgO-B O 2 3 ceramics were achieved at 975°C at x = 2 and y = 20. In particular, comprehensive comparison of the ceramic properties sintered at same low sintering temperature revealed that the ceramics with x = 6, y = 15 sintered at 950°C achieved good microwave dielectric properties with a ε of 6.72, Q × f of 83,205 GHz, and τ of – 65.05 r f ppm/°C. The ceramic with x = 8, y = 5 sintered at 925°C also achieved good microwave dielectric properties of ε = 6.64, Q × f = 78,173 GHz, and τ = – 57.27 ppm/°C. r f 3MgO-B O -x wt%BCB-ywt%H BO (x = 6, y = 15 or 2 3 3 3 x = 8, y = 5) had excellent microwave dielectric proper- Figure 8. XRD and SEM results of 3MgO-B O -xwt%BCB- 2 3 ties and can also be produced at low cost. Both cera- ywt%H BO (x = 6,8,y = 5,15)ceramics co-fired with silver pow- 3 3 der (The inset shows the EDS analysis of a 3MgO-B O mics could be co-fired with Ag, suggesting that they 2 3 -8 wt%BCB-5 wt%H BO sample co-fired with Ag). 3 3 are promising for 5 G applications, provided that τ can be further optimized to zero. To investigate whether the 3MgO-B O 2 3 -6 wt%BCB-15 wt%H BO and 3MgO-B O Acknowledgments 3 3 2 3 -8 wt%BCB-5wt%H BO ceramics could reacted with 3 3 This work was supported by Natural Science Foundation of silver electrodes or not, the two calcined powders China (Nos. 61761015 and12064007), Natural Science were mixed with 20 wt% Ag powder and sintered at Foundation of Guangxi (Nos. 2018GXNSFFA050001, 950°C and 925°C for 4 hours, respectively. Figure 8 2017GXNSFDA198027 and 2017GXNSFFA198011), High- Level Innovation shows the XRD patterns and backscattered electron Team and Outstanding Scholar Program of Guangxi diagrams of the samples. The XRD shows that Ag was Institutes. presented as a single phase and the EDS displays that the bright particles in the main ceramic matrix were silver, which further confirms that there is no reaction Disclosure statement between the silver and 3MgO-B O -8 wt%BCB-5 wt%H 2 3 3 No potential conflict of interest was reported by the author(s). BO and 3MgO-B O -6 wt%BCB-15 wt%H BO . All these 3 2 3 3 3 results prove the potential application of both ceramics in LTCC technology. Funding This work was supported by the National Natural Science 4. Conclusion Foundation of China [61761015]; National Natural Science In this study, 3MgO-B O -xwt%BCB-ywt%H BO 2 3 3 3 Foundation of China [12064007]; Natural Science Foundation of Guangxi [2017GXNSFFA198011]; Natural Science Foundation (where x = 2, 4, 6, and 8; y = 0, 5, 10, 15, and 20) of Guangxi [2017GXNSFDA198027]; Natural Science Foundation ceramics have been synthesized using the solid state of Guangxi [2018GXNSFFA050001]. reaction method. When y = 0, the ceramics consist of two phases, namely Mg B O and MgO. As x increased, 3 2 6 the main diffraction peak of MgO phase gradually References decreased while the diffraction peak of Mg B O gra- 3 2 6 dually increased. As x was constant, the diffraction [1] Guo HH, Zhou D, Du C, et al. 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