Effect of polymer derived SiBN ceramic components on thermal stability and electromagnetic wave transparency
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摘要: 对聚硅硼氮烷(PSNB)、三甲胺环硼氮烷(PBN)及混合先驱体陶瓷化过程分别进行了研究，掌握了热处理温度对先驱体转化陶瓷微结构及性能的影响规律。经NH3裂解后，聚合物转化陶瓷(PDC)-SiBN中形成了B—Si—O—N多元网络，具有良好的抗析晶能力，经过不超过1500℃的热处理后，陶瓷抗吸潮能力提升，介电常数在3.0~3.6之间，损耗约0.003。经NH3裂解的PDC-BN中形成了B—N—O结构，随温度升高逐渐分解，转变为BN。将先驱体按照一定比例混合，可以实现对聚合物转化陶瓷元素组分的调控。混合先驱体转化陶瓷中由于异质界面的存在及多元网络减少，陶瓷热稳定性及介电性能均介于单种先驱体转化陶瓷之间，具有一定的性能可设计性。Abstract: The ceramization process of polyborosilazane (PSNB), tris(methylamino)borane (PBN) and mixed precursors were studied respectively, and the influence of heat treatment temperature on the microstructure and properties of polymer derived ceramics was mastered. After pyrolysis under NH3, the B—Si—O—N multielement network was formed in PDC-SiBN, which had good crystallization resistance. After heat treatment at less than 1500℃, the moisture resistance of ceramics was improved, the dielectric constant was between 3.0 and 3.6, and the loss was about 0.003. After pyrolysis under NH3, the B—N—O structure was formed in PDC-BN, which gradually decomposed into BN with the increase of temperature. The precursor can be mixed in a certain proportion to control the elements of polymer derived ceramics. Due to the existence of heterogeneous interfaces in the mixed precursor derived ceramics, the multiple networks were reduced. The thermal stability and dielectric properties of mixed polymer derived ceramics are between those of single polymer derived ceramics, which have certain performance designability.
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Keywords:
- polymer derived ceramics /
- electromagnetic wave transparency /
- thermal stability /
- PSNB /
- PBN
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图 1 聚硅硼氮烷(PSNB)先驱体特征：(a)分子结构示意图；(b) TG-DSC曲线
Figure 1. Characteristics of polyborosilazane (PSNB): (a) Molecule structure; (b) TG-DSC curves
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图 2 NH3裂解后SiBN陶瓷的Raman图谱
ID—Intensity of D peak ; IG—Intensity of G peak
Figure 2. Raman spectrum of SiBN ceramic after pyrolysis under NH3
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图 3 NH3裂解后SiBN陶瓷XPS图谱：(a)全谱；Si (b)、B (c)、N (d)、O (e)、C (f)元素的高分辨图谱
Figure 3. XPS spectra of elements in SiBN ceramic after pyrolysis under NH3: (a) Full spectrum; High-resolution spectra of Si (b), B (c), N (d), O (e) and C (f) in ceramic
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图 4 不同温度热处理SiBN陶瓷后性能变化：(a)质量变化；(b)密度及开气孔率；(c)线收缩率；(d) XRD图谱
Figure 4. Performance evolution of SiBN ceramics after heat treatment at different temperatures: (a) Mass residual; (b) Density and open porosity; (c) Linear shrinkage; (d) XRD patterns of SiBN ceramics
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图 5 陶瓷化过程中PSNB和不同温度热处理后SiBN陶瓷的红外图谱
Figure 5. FTIR spectra of PSNB during ceramization process and SiBN ceramics after heat treatment at different temperatures
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图 6 不同温度热处理后SiBN陶瓷XPS高分辨图谱：(a) Si；(b) N；(c) B
Figure 6. XPS high-resolution spectra of elements in SiBN ceramic after heat treatment at different temperatures: (a) Si; (b) N; (c) B
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图 7 不同温度热处理后SiBN陶瓷介电性能：(a)介电常数；(b)介电损耗
Figure 7. Dielectric properties of SiBN ceramics after heat treatment at different temperatures: (a) Dielectric constant; (b) Dielectric loss
ε'—Real part of dielectric constant; ε''—Imaginary part of dielectric constant
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图 8 三甲胺环硼氮烷(PBN)先驱体特征：(a)分子结构示意图；(b) TG-DSC曲线
Figure 8. Characteristics of tris(methylamino)borane (PBN): (a) Molecule structure; (b) TG-DSC curves
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图 9 NH3裂解后BN陶瓷XPS图谱：全谱(a)及B (b)、N (c)、O (d)、C (e)元素的高分辨图谱
Figure 9. XPS spectra of elements in BN ceramic after pyrolysis under NH3: Full spectrum (a) and high-resolution spectra of B (b), N (c), O (d) and C (e) in ceramic
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图 10 不同温度热处理后BN陶瓷性能：(a)质量变化；(b) XRD图谱；(c) 1600℃热处理后BN陶瓷显微结构
Figure 10. Properties of BN ceramics after heat treatment at different temperatures: (a) Mass residual; (b) XRD patterns of BN ceramics; (c) Microstructure of BN ceramic after heat treatment at 1600℃
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图 11 陶瓷化过程中PBN和不同温度热处理后BN陶瓷的红外图谱
Figure 11. FTIR spectra of PBN during ceramization process and BN ceramics after heat treatment at different temperatures
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图 12 不同温度热处理后BN陶瓷XPS图谱：B (a)和N (b)元素的高分辨图谱
Figure 12. XPS spectra of elements in BN ceramic after heat treatment at different temperatures: High-resolution spectra of B (a) and N (b) elements in BN ceramics
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图 13 不同温度热处理后BN陶瓷介电性能：(a) 介电常数；(b) 介电损耗
Figure 13. Dielectric properties of BN ceramics after heat treatment at different temperatures: (a) Dielectric constant; (b) Dielectric loss
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图 15 混合先驱体陶瓷化过程：(a)理论和实际产率；(b)裂解后陶瓷中B元素含量
Figure 15. Ceramization process of mixed precursor with different proportions: (a) Theoretical and actual yield; (b) B element content of ceramics derived from mixed precursor
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图 16 混合先驱体转化SiBN陶瓷XPS图谱：全谱(a)及Si (b)、B (c)、N (d)、O (e)、C (f)元素的高分辨图谱
Figure 16. XPS spectra of elements in mixed precursor derived SiBN ceramic: Full spectrum (a) and high-resolution spectra of Si (b), B (c), N (d), O (e) and C (f) in ceramic
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图 17 不同比例混合先驱体转化陶瓷介电性能：(a) 介电常数；(b) 介电损耗；(c) 介电常数实部随B含量变化关系
Figure 17. Dielectric properties of mixed precursor derived ceramics with different precursor proportions: (a) Dielectric constant; (b) Dielectric loss; (c) Relationship between real part of permittivity and B content
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图 18 不同温度热处理后不同比例混合先驱体转化陶瓷的XRD图谱
Figure 18. XRD patterns of mixed precursor derived ceramics with different precursor proportions after heat treatment at different temperatures
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图 19 不同温度热处理后混合先驱体转化SiBN陶瓷XPS高分辨图谱：(a) Si；(b) N；(c) B
Figure 19. XPS high-resolution spectra of elements in mixed precursor derived SiBN ceramics after heat treatment at different temperatures: (a) Si; (b) N; (c) B
表 1 PSNB先驱体及在不同气氛下裂解后陶瓷(PDC)元素含量及产率
Table 1 Element contents and yields of PSNB and polymer derived ceramics (PDC) after pyrolysis in different atmospheres
Element content/wt% PDC
yield/%Si B N O C PSNB 34-36 5-7 24-26 1-2 27-29 — 900℃-N2 52.68 — 17.99 14.90 14.43 83.67 900℃-NH3 48.91 2.80 22.65 7.79 0.60 79.13 
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表 2 PBN先驱体及在NH3气氛下裂解后陶瓷元素含量及产率
Table 2 Element content and yield of PBN and PDC after pyrolysis under NH3
Element content/wt% PDC yield/% B N O C PBN 19.64 50 1-2 21.43 — 800℃-NH3 34.46 36.70 23.96 4.24 44.38
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表 3 不同比例混合先驱体产率及裂解后陶瓷中B元素含量
Table 3 Yield and B element content of ceramics derived from mixed precursor with different proportions
Sample m(PSNB)/
m(PBN)Curing
yield/%PDC
yield/%B content/wt% S-SiBN 1∶0 98.65 79.13 2.80 S-31 3∶1 91.24 65.26 9.02 S-21 2∶1 85.68 59.38 12.13 S-11 1∶1 83.89 62.79 15.27 S-12 1∶2 68.65 60.94 20.05 S-13 1∶3 65.33 58.57 21.03 S-BN 0∶1 59.71 44.38 34.46 Note: m(PSNB)/m(PSN)—Mass ratio of PSNB precursor to PSN precursor.
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[1] SUZDAL'TSEV E I. Radio-transparent ceramics: Yesterday, today, tomorrow[J]. Refractories and Industrial Ceramics,2015,55(5):377-390. DOI: 10.1007/s11148-015-9731-6
[2] 张大海, 黎义, 高文, 等. 高温天线罩材料研究进展[J]. 宇航材料工艺, 2001, 31(6):1-3. ZHANG Dahai, LI Yi, GAO Wen, et al. Development and application of high temperature radome materials[J]. Aerospace Materials & Technology,2001,31(6):1-3(in Chinese).
[3] 张煜东, 苏勋家, 侯根良. 高温透波材料研究现状和展望[J]. 飞航导弹, 2006(3):56-58. ZHANG Yudong, SU Xunjia, HOU Genliang. Research status and prospect on high temperature wave transparent materials[J]. Aerodynamic Missile Journal,2006(3):56-58(in Chinese).
[4] 崔雪峰, 李建平, 李明星, 等. 氮化物基陶瓷高温透波材料的研究进展[J]. 航空材料学报, 2020, 40(1):21-34. CUI Xuefeng, LI Jianping, LI Mingxing, et al. Research progress of nitride based ceramic high temperature wave transparent materials[J]. Journal of Aeronautical Materials,2020,40(1):21-34(in Chinese).
[5] 孙聪. 高超声速飞行器强度技术的现状、挑战与发展趋势[J]. 航空学报, 2022, 43(6):8-27. SUN Cong. Development status, challenges and trends of strength technology for hypersonic vehicles[J]. Acta Aeronautica et Astronautica Sinica,2022,43(6):8-27(in Chinese).
[6] 李燚. 短时高温工作的透波隔热天线罩设计[J]. 无线互联科技, 2017(13):62-65. LI Yi. Design of the microwave transparent and heat insolated antenna that works in short-time high-tempera-ture[J]. Wireless Internet Technology,2017(13):62-65(in Chinese).
[7] 千粉玲, 谢志鹏, 孙加林, 等. Al2O3陶瓷微波介电性能的研究与进展[J]. 陶瓷学报, 2012, 33(4):519-527. QIAN Fenling, XIE Zhipeng, SUN Jialin, et al. Research status on microwave dielectric properties of Al2O3ceramics[J]. Journal of Ceramics,2012,33(4):519-527(in Chinese).
[8] 孙银宝, 张宇民, 韩杰才. 耐高温透波材料及其性能研究进展[J]. 宇航材料工艺, 2008, 38(3):11-14. SUN Yinbao, ZHANG Yumin, HAN Jiecai. High-tempera-ture resistant microwave-transmitting materials and their properties[J]. Aerospace Materials & Technology,2008,38(3):11-14(in Chinese).
[9] YANG X J, LI B, ZHANG C R, et al. Fabrication and properties of porous silicon nitride wave-transparent ceramics via gel-casting and pressureless sintering[J]. Materials Science and Engineering A,2016,663:174-180. DOI: 10.1016/j.msea.2016.03.116
[10] YANG X J, LI B, LI D, et al. High-temperature properties and interface evolution of silicon nitride fiber reinforced silica matrix wave-transparent composite materials[J]. Journal of the European Ceramic Society,2019,39(2):240-248.
[11] COLOMBO P, MERA G, RIEDEL R, et al. Polymer-derived ceramics: 40 years of research and innovation in advanced ceramics[J]. Journal of the American Ceramic Society,2010,93(7):1805-1837.
[12] 李斌. 氮化物陶瓷基耐烧蚀、透波复合材料及其天线罩的制备与性能研究[D]. 长沙: 国防科学技术大学, 2007. LI Bin. Preparation and performance of ablation resistant, wave-transparent nitride ceramic matrix composites and radome[D]. Changsha: National University of Defense Technology, 2007(in Chinese).
[13] TANG Y, WANG J, LI X D, et al. Polymer-derived SiBN fiber for high-temperature structural/functional applications[J]. Chemistry-A European Journal,2010,16(22):6458-6462. DOI: 10.1002/chem.200902974
[14] 黄先华, 刘勇, 张晨宇, 等. SiBN陶瓷纤维的脱碳工艺研究[J]. 合成纤维工业, 2017, 40(2):1-5. HUANG Xianhua, LIU Yong, ZHANG Chenyu, et al. Decarburization research of SiBN ceramic fibers[J]. China Synthetic Fiber Industry,2017,40(2):1-5(in Chinese).
[15] MAEDA M, MAKINO T. Low dielectric constant amorphous SiBN ternary films prepared by plasma-enhanced deposition[J]. Japanese Journal of Applied Physics,1987,26(5R):660. DOI: 10.1143/JJAP.26.660
[16] BARTA J, MANELA M, FISCHER R. Si3N4 and Si2N2O for high performance radomes[J]. Materials Science and Engineering,1985,71:265-272. DOI: 10.1016/0025-5416(85)90236-8
[17] GANESH I. Novel composites of β-SiAlON and radome manufacturing technology developed at ARCI, hyderabad, for hypervelocity vehicles[J]. Bulletin of Materials Science,2017,40(4):719-735. DOI: 10.1007/s12034-017-1424-y
[18] LONG X, SHAO C W, WANG Y D. Effects of boron content on the microwave-transparent property and high-temperature stability of continuous SiBN fibers[J]. Journal of the American Ceramic Society,2020,103(8):4436-4444. DOI: 10.1111/jace.17151
[19] TAVAKOLI A H, GERSTEL P, GOLCZEWSKI J A, et al. Kinetic effect of boron on the crystallization of Si3N4 in Si-B-C-N polymer-derived ceramics[J]. Journal of Materials Research,2011,26(4):600-608. DOI: 10.1557/jmr.2010.53
[20] 李贞, 殷小玮, 成来飞, 等. 液态聚硼硅氮烷的陶瓷化过程[J]. 硅酸盐学报, 2012, 40(7):979-982. LI Zhen, YIN Xiaowei, CHENG Laifei, et al. Polymer-ceramic conversion of liquid polyborosilazanes[J]. Journal of the Chinese Ceramic Society,2012,40(7):979-982(in Chinese).
[21] 国家质量技术监督局. 致密定形耐火制品体积密度、显气孔率和真气孔率试验方法: GB/T 2997—2000[S]. 北京: 中国标准出版社, 2000. State Bureau of Quality and Technical Supervision of China. Test method for bulk density, apparent porosity and true porosity of dense shaped refractory products: GB/T 2997—2000[S]. Beijing: China Standards Press, 2000(in Chinese).
[22] GALUSEK D, RESCHKE S, RIEDEL R, et al. In-situ carbon content adjustment in polysilazane derived amorphous SiCN bulk ceramics[J]. Journal of the European Ceramic Society,1999,19(10):1911-1921. DOI: 10.1016/S0955-2219(98)00288-X
[23] YE F, ZHANG L T, YIN X W, et al. Dielectric and EMW absorbing properties of PDCs-SiBCN annealed at different temperatures[J]. Journal of the European Ceramic Society,2013,33(8):1469-1477. DOI: 10.1016/j.jeurceramsoc.2013.01.006
[24] XU Y, HU J, TAO M, et al. Study of pyrolysis mechanism of SiBCN polymer precursor[J]. Aerospace Materials & Technology,2018,48(1):44-48.
[25] MO R, YIN X W, YE F, et al. Mechanical and microwave absorbing properties of Tyranno® ZMI fiber annealed at elevated temperatures[J]. Ceramics International,2017,43(12):8922-8931. DOI: 10.1016/j.ceramint.2017.04.030
[26] ZHANG X W, YOU J B, CHEN N F. Recent advances in synthesis and properties of cubic boron nitride films[J]. Journal of Inorganic Materials,2007,22(3):385-390.
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目的
聚合物转化陶瓷(PDC)具有先驱体成分可设计、陶瓷组分可调等优点，通过PDC法制备的陶瓷已经广泛应用于各行各业，取得了很多成果，在热透波领域具有极大的应用前景。针对聚合物陶瓷化过程以及聚合物转化陶瓷微结构及性能的研究对复合材料基体的制备具有指导意义。相比Si3N4等二元陶瓷，多组元陶瓷能够在更高温下保持非晶态，具有更加优异的高温稳定性、高温抗氧化性等性能，很有潜力应用于透波陶瓷材料中。针对聚合物转化陶瓷中不同元素组分及其含量对陶瓷性能的影响已有大量研究，但对于多种先驱体共混转化陶瓷的研究还鲜有报道。共混先驱体陶瓷化过程尚不清晰，不同先驱体裂解后元素的键合方式、元素含量是否会相互影响，以及转化获得的陶瓷的热稳定性能、介电性能特征还有待研究。
方法采用德国NETZSCH公司生产的STA 449 F3型同步热分析仪(TG-DSC)表征先驱体的陶瓷化过程。采用荷兰帕纳科公司生产的X' Pert Pro型X射线衍射仪(XRD)测试陶瓷的物相以及结晶度。采用雷尼绍公司生产的激光拉曼光谱仪(Raman)表征陶瓷中碳的存在形式。用岛津Kratos公司生产的Axis Supra型X射线光电子能谱(XPS)以及IRAfinitty-1S型傅里叶变换红外光谱仪(FT-IR)表征陶瓷的键合组成。采用日本日立公司生产的S-4700型场发射扫描电子显微镜(SEM)观察陶瓷的微观形貌。采用美国FEI公司生产的Tecnai G2 F30S-TWIN型透射电镜(TEM)观察陶瓷的微观结构。使用碳硫分析仪和氧氮联测仪测试陶瓷中C、O、N的质量分数；采用美国Thermo Fisher Scientific公司生产的Thermo ICP 6300型电感耦合等离子体光谱/质谱(ICP)测试陶瓷中B的质量分数；采用重量法测试陶瓷中Si的质量分数。采用日本Anritsu公司生产的MC-4644A型矢量网络分析仪(VNA)测试陶瓷的电磁透波性能。
结果(1)在NH3气氛下裂解可以实现PSNB先驱体中含C烷基的去除，得到聚合物转化SiBN陶瓷。裂解后陶瓷为非晶态，由多元B-Si-O-N网络组成，具有优异的热稳定性，抗析晶温度可达1600℃。热处理温度高于1300℃时，开始出现相分离，B-Si-O-N网络逐渐分解，转变为Si-O-N、Si-N、B-N。同时，不超过1500℃的热处理使陶瓷稳定性提升，吸潮现象得到缓解，介电常数实部及损耗有所降低；热处理温度超过1500℃时，陶瓷中晶界的产生，使介电常数实部及损耗迅速升高。(2)PBN先驱体在NH3气氛下裂解后得到非晶BN陶瓷，由于先驱体性质，BN陶瓷O含量较高，以B-N-O形式存在。随热处理温度升高，陶瓷中含氧相首先发生分解，B-N-O逐渐转变为B-N，这也造成了热处理过程中较大的质量损失。热处理温度超过1000℃时，PDC-BN开始析晶，介电常数也随之升高。(3)混合先驱体经固化后，官能团特征表现为两种先驱体的加和，先驱体结构并未受到混合和固化过程的影响。陶瓷产率与理论值具有一定一致性，并且通过比例调控，实现了PDC元素组分的调控。900℃裂解后，陶瓷中以Si-O-N、B-N为主，相比单种先驱体转化陶瓷，由于先驱体混合带来的异质界面，裂解态下已经出现多元陶瓷网络的分解，热稳定性能介于PDC-SiBN和PDC-BN之间。陶瓷的介电常数以及析晶温度受先驱体比例影响，面向不同使用环境，可通过比例调控，对聚合物转化陶瓷的性能进行设计。
结论PSNB经NH3裂解后，基本实现陶瓷化，形成了B-Si-O-N多元网络结构，具有良好的热稳定性，抗析晶温度可达1600℃，但热处理温度超过1300℃时，多元网络分解，开始出现相分离。热处理温度不超过1500℃时，PDC-SiBN抗吸潮性能提升，介电常数和损耗有所降低，超过1500℃时，晶界的产生使材料透波性能下降。PBN经NH3裂解后，形成了以B-N-O结构为主的陶瓷，随温度升高，含氧相逐渐分解，转变为h-BN。由于PBN对氧气和水比较敏感，陶瓷中O含量较高，热处理后质量损失较大，且热处理温度超过1000℃时，陶瓷开始出现析晶现象，介电常数增大。混合先驱体经NH3裂解后，陶瓷中元素组分可由先驱体比例调控，在先驱体共同陶瓷化的过程中，其陶瓷产率与理论产率相吻合，但由于异质界面的存在，多元网络减少。混合先驱体转化陶瓷热稳定性及介电性能均介于两种PDC之间，具有一定的性能可设计性。
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随着航空航天技术的发展，高超音速飞行器得到了极大发展，因此需要综合性能更加优异的高温透波材料。聚合物转化陶瓷的热稳定性能受元素组分影响很大，但对于多种先驱体共混转化陶瓷的研究还鲜有报道。共混先驱体陶瓷化过程尚不清晰，不同先驱体裂解后元素的键合方式、元素含量是否会相互影响，以及转化获得的陶瓷的热稳定性能、介电性能特征还有待研究。本文对PSNB、PBN、混合先驱体陶瓷化过程及微结构性能变化分别进行了研究，通过先驱体混合，实现了聚合物转化Si-B-N陶瓷元素组分的调控，使聚合物转化陶瓷具有一定的性能可设计性。PSNB经NH3裂解后，基本实现陶瓷化，形成了B-Si-O-N多元网络结构，具有良好的热稳定性，抗析晶温度可达1600℃，但热处理温度超过1300℃时，多元网络分解，开始出现相分离。热处理温度不超过1500℃时，PDC-SiBN抗吸潮性能提升，介电常数和损耗有所降低，超过1500℃时，晶界的产生使材料透波性能下降。PBN经NH3裂解后，形成了以B-N-O结构为主的陶瓷，随温度升高，含氧相逐渐分解，转变为h-BN。由于PBN对氧气和水比较敏感，陶瓷中O含量较高，热处理后质量损失较大，且热处理温度超过1000℃时，陶瓷开始出现析晶现象，介电常数增大。混合先驱体经NH3裂解后，陶瓷中元素组分可由先驱体比例调控，在先驱体共同陶瓷化的过程中，其陶瓷产率与理论产率相吻合，但由于异质界面的存在，多元网络减少。混合先驱体转化陶瓷热稳定性及介电性能均介于两种PDC之间，具有一定的性能可设计性。
Dielectric properties of mixed precursor derived ceramics with different precursor proportions: (a) Dielectric constant and (b) loss of ceramics. (c) Relationship between real part of permittivity and B content
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