Electromagnetic properties and microwave absorption performances of nickel-doped SiCN ceramics pyrolyzed at different temperatures

Accepted Manuscript Electromagnetic properties and microwave absorption performances of nickel-doped SiCN ceramics pyrolyzed at different temperatures Yu Liu, Xiao Lin, Hongyu Gong, Yujun Zhang, Yurun Feng, Junjie Mao, Bingying Xie PII:

S0925-8388(18)33164-5

DOI:

10.1016/j.jallcom.2018.08.283

Reference:

JALCOM 47371

To appear in:

Journal of Alloys and Compounds

Received Date: 13 June 2018 Revised Date:

27 August 2018

Accepted Date: 28 August 2018

Please cite this article as: Y. Liu, X. Lin, H. Gong, Y. Zhang, Y. Feng, J. Mao, B. Xie, Electromagnetic properties and microwave absorption performances of nickel-doped SiCN ceramics pyrolyzed at different temperatures, Journal of Alloys and Compounds (2018), doi: 10.1016/j.jallcom.2018.08.283. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Electromagnetic properties and microwave absorption performances of nickel-doped SiCN ceramics pyrolyzed at different temperatures Yu Liua,b, Xiao Lina,b, Hongyu Gonga,b∗, Yujun Zhanga,b, Yurun Fenga,b, Junjie Maoa,b, Bingying Xiea,b Key laboratory for Liquid-Solid Structural Evolution & Processing of Materials of Ministry of

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a

Education, Shandong University, Jingshi Road 17923, Jinan250061, Shandong, China b

Key laboratory of Special Functional Aggregated Materials, Ministry of Education, Shandong

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University, Jingshi Road 17923, Jinan250061, Shandong, China

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Abstract: Nickel-doped polymer derived SiCN ceramics (PDCs-SiCN (Ni)) were successfully prepared via a polymer-derived method from polysilazane and nickel oxide, and pyrolyzed at 900

-1400

. The effects of pyrolysis temperatures on phase

composition, microstructure and microwave absorption properties of PDCs-SiCN (Ni)

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were investigated. Results showed that the polymer-to-ceramic conversion was completed at around 800

. Besides carbon nanotubes were formed in the pore area

of SiCN matrix through the catalysis of Ni. The electromagnetic (EM) parameters

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varied with the different pyrolysis temperatures. When the PDCs-SiCN (Ni) , the minimum reflection loss value reached -48.5 dB at 15.1 GHz,

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pyrolyzed at 1200

exhibiting the best EM wave absorption properties. Keywords: PDCs-SiCN (Ni); Nickel oxide; Pyrolysis temperatures; Carbon nanotubes; Microwave absorption performances.

1. Introduction ∗

Corresponding author. Tel / Fax: +86-531-88399760; E-mail addresses: [email protected] 1

ACCEPTED MANUSCRIPT The rapid development of radar technology and wireless communications [1-3] have caused an increasing number of problems like electromagnetic (EM) pollution. Thus EM wave absorption materials are widely used to overcome these problems

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[4-6]. Polymer derived SiCN ceramics (PDCs-SiCN) have attracted many interests because such ceramics possess dielectric properties attributed to the existence of free-carbon nanodomains [7]. Compared with other EM wave absorbers such as

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metals, ferrites or carbon nanotubes, the PDCs-SiCN perform better thermal stability,

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corrosion resistance and oxidation resistance [8, 9] which make PDCs-SiCN attain a wide application prospect as EM wave absorbing materials. Besides, the polymer-derived method provides many potential advantages like uniformity and low processing temperature [10, 11].

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In order to improve EM wave absorbing properties of PDCs-SiCN, many efforts have been made. According to the reported literature [12], PDCs-SiCN contain a large number of free carbons and crystallized carbons such as carbon nanotubes, carbon

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nanowires or graphene-like carbons, which can improve dielectric properties. The

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carbon nanowires or nanotubes can be formed by adding catalytic metals [13]. Q. Li et al. [14] improved dielectric performances of SiCN ceramics by preparing ferrocene-modified PDCs-SiCN and nanostructured carbons could also be in-situ fabricated.

In addition, the PDCs-SiCN alone may be unable to meet the requirement of impedance matching characteristic because of their poor magnetic properties [15]. Thus various magnetic materials have been used to prepare composites in order to 2

ACCEPTED MANUSCRIPT increase magnetic properties and tune the electromagnetic parameters [16-19]. C. Zhou et al. [20] prepared Si–C–N–Fe ceramics from polysilazane and iron (III) acetylacetonate, and the final ceramics exhibited ferromagnetic behavior. Nickel as a

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magnetic material can increase magnetic properties of materials [21, 22]. On the other hand, the nickel are also expected to promote the crystallization process of carbon through catalysis and improve dielectric properties.

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In our previous study [23], nickel-doped polymer derived SiCN ceramics

at 1000

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(PDCs-SiCN (Ni)) were synthesized using different nickel sources through pyrolysis . By comparison, the PDCs-SiCN (Ni) with nickel oxide (NiO) as nickel

source exhibited the strongest loss capacity though the reflection loss is not the lowest. In order to find the optimal pyrolysis temperature, PDCs-SiCN (Ni) were pyrolyzed at using NiO as nickel source. The phase

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temperatures from 900 to 1400

compositions, microstructures and microwave absorbing performances in 2-18 GHz

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of the final ceramics were investigated.

2. Experimental

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A liquid-phase polysilazane (PSZ, Shanghai Haiyi Technology Trade Co., Ltd,

China) was used as precursor, and Fig. 1 shows the molecular structure of PSZ. Nickel oxide (NiO, 25-35 nm, Shanghai Macklin Biochemical Co., Ltd, China) was added by weight ratio of 10 wt%. Then, the as-received mixture was stirred in a suction flask for 30 min and cross-linked at 600

for 120 min in a flowing nitrogen

(N2) environment. The cross-linked polymer was ball-milled for 40 min and passed through a 200 mesh sieve. The obtained powders were then pressed into green bodies 3

ACCEPTED MANUSCRIPT with a shape of flaky under a pressure of 20 MPa. Finally, the green bodies were pyrolyzed at 900

, 1000

, 1100

, 1200

, 1300

and 1400

ºfor 120 minº

respectively in a tube furnace under a N2 atmosphere to obtain PDCs-SiCN (Ni).

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The structures of PSZ, Ni-containing PSZ (PSZ (Ni)) and cross-linked PSZ (Ni) precursors were carried out on Fourier-transform infrared spectroscopy (FT-IR, TENSOR-37, Bruker, Germany). The thermal analysis for cross-linked polymer was /min under N2 atmosphere by thermal

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analyzed with a ramping rate of 10

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gravimetric analysis (TGA, DSC-404, Netzsch, Germany). The compositions of PDCs-SiCN (Ni) were measured using X-ray diffraction (XRD, D/MAX-Ultima IV, Rigaku, Japan) and scanning electron microscope (SEM, EVO18, Zeiss, German) equipped with an energy dispersive spectrometer (EDS). The morphology and

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microstructure of the materials were observed by a transmission electron microscope (TEM, JEM-1200EX, JEOL, Japan) and a high-resolution transmission electron microscopy (HRTEM, Tecnai G2 F20 S-TWIN, FEI, USA) operated at 200 kV. The

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Raman spectra was performed by a confocal Raman microscopy (RMS, Renishaw,

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UK) using an excitation laser wavelength of 514.5 nm. The complex permittivity and permeability can be obtained by measuring EM parameters using a vector network analyzer (5244A, Agilent-N, USA) in the 2-18 GHz ranges. To prepare samples used for EM measurement, the materials were mixed with wax and then pressed into a toroid with an inner diameter of 3.0 mm, an outer diameter of 7.0 mm and a thickness of 2.0 mm.

3. Results and discussion 4

ACCEPTED MANUSCRIPT 3.1 Thermal behavior of cross-linked PSZ (Ni) precursors. To study the structural evolution during the cross-linking process, the FT-IR spectrum of PSZ, PSZ (Ni) and cross-linked PSZ (Ni) precursors at different heated

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temperatures are presented in Fig. 2. The vibration bands at 3381 cm−1 and 1182 cm−1 (N-H), 3047 cm-1 (C-H in C=C-H), 2955 cm−1 and 2898 cm-1 (C-H in CH3), 2141 cm−1 (Si-H), 1591 cm−1 (C=C), 1406 cm−1 (Si-vinyl), 1250 cm−1 (Si-CH3), 949 cm−1

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(Si-N) and 820 cm−1 (Si-C) [24, 25] were observed in the FT-IR spectra of PSZ. These

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bands still existed in PSZ (Ni), and the intensity of all peaks showed a steady fall with the increase of cross-linking temperature. When the temperature increased to 600

,

the stretch vibration peaks of C-H, C=C, Si-H and N-H almost disappeared. As the temperature rose to 800

, all peaks related to organic groups disappeared while the

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broad superimposed peak of Si-C and Si-N still retained indicating the polymer-to-ceramic conversion was completed [26]. As shown in Fig. 3, the decalescence peaks of DTA curve were corresponding to

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the sharp fall stages of TG curve respectively, indicating that the conversion was an

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endothermic process. The first weight loss was about 8 wt% at 15–350

which

might be due to the escape of non-crosslinked small molecules from system [27, 28], and the corresponding endothermal peak located at 228 was 14 wt% at 350-700

. The second weight loss

and the corresponding exothermic peak appeared at 547

.

In this stage, breakage and rearrangement of molecular chains occurred, releasing a large number of small molecular gas meanwhile [28].

5

ACCEPTED MANUSCRIPT 3.2 Phase compositions. The XRD patterns in Fig. 4 demonstrate the phase compositions of PDCs-SiCN (Ni) pyrolyzed at different temperatures. The main diffraction peaks of the ceramics at 900 were located at 44.46 , 51.82

and 76.6

which were well consistent

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and 1000

with these of the PDF Card No. 65-0380, indicating the main phase was Ni. The diffraction peak at 26.26

corresponding to carbon (PDF Card No. 41-1487) could , the diffraction peaks of Ni

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also be observed. When pyrolysis temperature was 1100

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become lower in intensity and the peaks of Ni2Si (PDF Card No. 50-0779) appeared. The reason might be that higher temperature could promote transformation form Ni to Ni2Si in the obtained materials [29]. Meanwhile, Si3N4 (PDF Card No. 09-0250) also appeared, and along with the rise of temperature, the intensities of carbon, Ni2Si and

pyrolyzed at 1300

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Si3N4 increased suggesting the improvement of crystallization degrees. When , a small quantity of Si2N2O (PDF Card No. 47-1627) also existed

[30].

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in the ceramics. The O might be introduced during the during the preparation process

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The carbon phases in PCDs-SiCN (Ni) were investigated by Raman microscopy, and the results are shown in Fig. 5. The Raman spectra of all ceramics contained both D band (related to the sp3 defects within carbons) and G band (related to the sp2-hybridized carbons) implying the existence of free carbons [31]. In order to further analyze the features of free carbons, Raman spectra were fitted by the Gaussian curves and the parameters are shown in Table 1. With the increase of temperature, the positions of D peak (ωD) and G peak (ωG) were shifted to higher 6

ACCEPTED MANUSCRIPT frequency, and the full width half maximum of D peak (FWHHD) and G peak (FWHHG) showed a decrease. Generally, the intensity ratio of the D band and G band (ID / IG) is widely used to estimate the order degree of carbon clusters in materials [32,

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33]. When the temperature rose, the ID / IG ratio declined stably, which could be attributed to the ordering and growth of carbon clusters increasing the degree of

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carbon crystallization [34].

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3.3 Microstructures.

Fig.6 shows the SEM images of PDCs-SiCN (Ni) pyrolyzed at different temperatures and EDS spectra of the ceramics pyrolyzed at 900

. As shown in Fig. 6 (a)-(f), the

typical amorphous structure was observed in all ceramics. Take the ceramics as an example, it could be seen from Fig.6 (g) that the main

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pyrolyzed at 900

elements in gray matrix were Si, C and N. Besides a small amount of bright grains distributed in the gray matrix. According to Fig. 6 (h), the main element of grains was

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Ni which was consistent with the XRD results. The SEM images of all ceramics

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revealed the existent of nanotubes in the pore area of matrix which might provide the materials with advantages in wave absorption. Nevertheless SEM images failed to demonstrate microstructures in detail because of the limitation of the resolution. As shown in TEM images of the ceramics pyrolyzed at 1000

(Fig. 7 (a) (b)), black

sphere-like particles which were Ni according to diffraction patterns with a diameter distribution of 10–50 nm dispersed in the matrix. The corresponding HRTEM images in Fig. 7 (c) clearly displayed that the lattice fringe spacing of Ni was 0.203 nm, 7

ACCEPTED MANUSCRIPT consistent with the (111) planes of the face centered cubic structured Ni, which is in accordance with the XRD results. The free carbons with turbostratic structure could also be observed, and the lattice plane spacing was about 0.34 nm, which

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corresponded to the (002) planes of graphite. Besides of Ni and carbons, amorphous SiCN matrix was shown in Fig. (c). A carbon nanotube with diameter about 40 nm could be clearly seen in Fig. (d). The formation of carbon nanotubes might be

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attributed to the catalyst of Ni [35]. To the best of our knowledge, the SiCN matrix

absorbing materials [36, 37].

3.4 Electromagnetic properties.

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can also reduce agglomeration and oxidation of Ni nanoparticles compared to metal

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The microwave absorbing behavior of materials depends on their dielectric properties and magnetic properties, which are represented by complex permittivity ( =   − ′′) and complex permeability (  =  −  ′′) [38]. Fig. 8 demonstrates

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the changes in the real part (ε′) and imaginary part (ε′′) of the complex permittivity

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with frequency for the ceramics pyrolyzed at different temperatures. As displayed in Fig. 8 (a), the ε′ values of the PDCs-SiCN pyrolyzed at 900

, 1000

and 1100

were quite similar, and when the pyrolysis temperature rose, the values of ε′ increased gradually which could be attributed to the increase of crystallization degree of carbon [39]. The higher ε′ values compared to some similar materials might be due to the existent of carbon nanotubes [15, 40]. A peak could be observed in the curves for all ceramics suggesting a resonance behavior, and the locations of peaks 8

ACCEPTED MANUSCRIPT varied with the different heat-treatment temperatures. The real permeability (μ′) and the imaginary permeability (μ′′) of the PDCs-SiCN (Ni) pyrolyzed at different temperatures are shown in Fig. 9. The resonance peaks -1200

, and showed a small but

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appeared for the ceramics pyrolyzed at 900

continuous upward shift in position with the increase of temperature. However, for the other ceramics the curves of both μ′ and μ′′ showed almost no dramatic changes

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with increasing frequency. The reason might be that almost all of Ni was converted into Ni2Si which possessed no magnetism.

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The dielectric loss tangent (tan =   /′) and magnetic loss tangent (tan =  / ′) of the PDCs-SiCN (Ni) pyrolyzed at different temperatures versus frequency are displayed in Fig. 10. The resonance peaks were detected in all tan curves,

was 1200

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corresponding to the peaks of complex permittivity. When the pyrolysis temperature ,ºthe maximum tan value was 5 indicating the highest dielectric loss.

Meanwhile, the tan displayed a similar tendency of μ′′ when the frequency

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increased. The PDCs-SiCN (Ni) pyrolyzed at 1000

exhibited the largest tan

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value 5.2 at 12 GHz.

3.5 Microwave absorption properties. Reflection loss (RL) is an important parameter to exhibit the EM absorption

properties of materials, and can be calculated as follows [41]:  = 20 log |( − 1)/( + 1)| where 

(1)

is the input impedance, which can be calculated by the following equation 9

ACCEPTED MANUSCRIPT [42]:  = $  / tan h &(2'()/c)√   ,

(2)

where  and represent relative permeability and permittivity of materials, ( is

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the frequency of the EM wave, d is the thickness of absorbing materials, and c is light velocity. Fig. 11 depicts the variation of RL of the PDCs-SiCN (Ni) pyrolyzed at different temperatures with frequency. When the ceramics pyrolyzed at 1200

, the

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minimum RL was -48.5 dB at 15.1 GHz with an effective bandwidth (RL < -10 dB) of

ceramics pyrolyzed at 1000

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0.6 GHz, exhibiting the best absorption properties. The maximum RL values for the and 1100

were -42 dB at 11.9 GHz and -30.8 dB at

15 GHz respectively. However, the RL curves of ceramics pyrolyzed at 900 and 1400

, 1300

showed no obvious peak suggesting weaker microwave absorption

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capabilities. It is worthy to note that in addition to the dielectric loss and the magnetic loss, the impedance matching is also an important factor to evaluate EM wave absorbing performances of materials [43, 44]. Thus the optical impedance matching

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endowed the ceramics pyrolyzed at 1200

with excellent EM wave absorption

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properties. To the best of our knowledge, in comparison to some other metal-doped SiCN ceramics and Ni-containing composites [45-47], the PDCs-SiCN (Ni) in this work had lower minimum reflection loss and thinner thickness, and thus possessed potential prospects in wave adsorbing materials.

4. Conclusions In summary, the PDCs-SiCN (Ni) were synthesized by the pyrolysis of 10

ACCEPTED MANUSCRIPT NiO-containing PSZ following the polymer derived method. The phase compositions, microstructures and EM wave absorbing properties of PDCs-SiCN (Ni) pyrolyzed at different temperatures were investigated. When the temperature rose to 800

the

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polymer-to-ceramic conversion was completed. The crystallization degree of carbons increased with the increase of pyrolysis temperature and the carbon nanotubes could be obtained in the ceramics through the catalysis of Ni, which were expected to give

with an effective bandwidth of 0.6

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15.1 GHz for the ceramics pyrolyzed at 1200

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the materials advantages in wave absorption. The minimum RL reaches -48.5 dB at

GHz indicating good EM wave absorption properties. Therefore the PDCs-SiCN (Ni) could be regarded as a high-performance microwave absorbing material.

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Acknowledgment

The authors would like to extend their sincere appreciation to the National Natural

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Science Foundation of China (No.51572154) for its funding.

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[43] Y.J. Chen, P. Gao, R.X. Wang, C.L. Zhu, L.J. Wang, Porous Fe3O4/Carbon Core/Shell Nanorods: Synthesis and Electromagnetic Properties, J. Phys. Chem. C 115 (2011) 10061-10064. [44] J.P. Wang, J. Wang, R.X. Xu, Y. Sun, B. Zhang, W. Chen, T. Wang, S. Yang, Enhanced microwave absorption properties of epoxy composites reinforced with Fe50Ni50-functionalized grapheme, J. Alloy. Compd. 653 (2015) 14-21. [45] Y.Z. Wang, Y.R. Feng, X. Guo, Y. Liu, H.Y. Gong, Electromagnetic and wave absorbing properties of Fe-doped polymer-derived SiCN ceramics, RSC Adv. 7 (2017) 16

ACCEPTED MANUSCRIPT 46215-46220. [46] B. Zhao, G. Shao, B.B. Fan, W. Li, X.X. Pian, R. Zhang, Enhanced electromagnetic wave absorption properties of Ni–SnO2 core–shell composites

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synthesized by a simple hydrothermal method, Mater. Lett. 121 (2014) 118–121. [47] S. Ryu, C.B. Mo, H. Lee, S.H. Hong, Fabrication Process and Electromagnetic Wave Absorption Characterization of a CNT/Ni/Epoxy Nanocomposite, J. Nanosci.

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ACCEPTED MANUSCRIPT Table captain Table 1. Raman spectra parameters of PDC-SiCN (Ni) ceramics pyrolyzed at different

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temperatures.

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ACCEPTED MANUSCRIPT Table 1. Raman spectra parameters of PDC-SiCN (Ni) ceramics pyrolyzed at different temperatures. ωD (cm-1)

FWHHD (cm-1)

ωG (cm-1)

FWHHG (cm-1)

ID/IG

900℃

1324.133

167.373

1569.315

115.545

2.161

1000℃

1340.052

196.784

1562.750

1100℃

1355.815

192.058

1565.570

1200℃

1346.664

176.996

1562.778

1300℃

1340.497

134.888

1572.401

1400℃

1398.687

33.197

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Temperature

1.626

117.262

1.619

116.640

1.631

101.914

1.603

37.487

0.700

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122.745

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1607.370

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ACCEPTED MANUSCRIPT Figure captions Fig. 1. Molecular structure of polysilazane. Fig. 2. FTIR spectra of PSZ, PSZ (Ni) and cross-linked PSZ (Ni) precursors at

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different heated temperature. Fig. 3. TG-DTA curves of cross-linked PSZ (Ni) precursor at a temperature range of 25–700℃.

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Fig. 4. XRD patterns of PDC-SiCN (Ni) pyrolyzed at different temperatures.

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Fig. 5. Raman spectra of PDC-SiCN (Ni) pyrolyzed at different temperatures. Fig. 6. SEM images of PDC-SiCN (Ni) pyrolyzed at 900℃ (a), 1000℃ (b), 1100℃ (c), 1200℃ (d), 1300℃ (e) and 1400℃ (f), and EDS spectra (g) (h) of PDC-SiCN (Ni) pyrolyzed at 900℃.

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Fig. 7. TEM and HRTEM images of PDC-SiCN (Ni) pyrolyzed at 1000℃. Fig. 8. Frequency dependence on real (a) and imaginary (b) parts of the complex permittivity for PDC-SiCN (Ni) pyrolyzed at different temperatures.

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Fig. 9. Frequency dependence on real (a) and imaginary (b) parts of the complex

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permeability for PDC-SiCN (Ni) pyrolyzed at different temperatures. Fig. 10. Frequency dependence on dielectric (a) and magnetic loss tangents (b) for PDC-SiCN (Ni) s pyrolyzed at different temperatures. Fig. 11. Frequency dependence on reflection loss (RL) for PDC-SiCN (Ni) pyrolyzed at different temperatures.

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Fig. 1. Molecular structure of polysilazane.

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Fig. 2. FTIR spectra of PSZ, PSZ (Ni) and cross-linked PSZ (Ni) precursors at

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different heated temperature.

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Fig. 3. TG-DTA curves of cross-linked PSZ (Ni) precursor at a temperature range of

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25–700℃.

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Fig. 4. XRD patterns of PDC-SiCN (Ni) pyrolyzed at different temperatures.

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Fig. 5. Raman spectra of PDC-SiCN (Ni) pyrolyzed at different temperatures.

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Fig. 6. SEM images of PDC-SiCN (Ni) pyrolyzed at 900℃ (a), 1000℃ (b), 1100℃ (c), 1200℃ (d), 1300℃ (e) and 1400℃ (f), and EDS spectra (g) (h) of PDC-SiCN (Ni) pyrolyzed at 900℃. 7

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1000℃.

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Fig. 7. TEM (a) (b) and HRTEM (c) (d) images of PDC-SiCN (Ni) pyrolyzed at

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Fig. 8. Frequency dependence on real (a) and imaginary (b) parts of the complex

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permittivity for PDC-SiCN (Ni) pyrolyzed at different temperatures.

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Fig. 9. Frequency dependence on real (a) and imaginary (b) parts of the complex

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permeability for PDC-SiCN (Ni) pyrolyzed at different temperatures.

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Fig. 10. Frequency dependence on dielectric (a) and magnetic loss tangents (b) for

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PDC-SiCN (Ni) pyrolyzed at different temperatures.

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Fig. 11. Frequency dependence on reflection loss (RL) for PDC-SiCN (Ni) pyrolyzed

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at different temperatures.

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ACCEPTED MANUSCRIPT PDCs-SiCN(Ni) were prepared from polysilazane and NiO, and pyrolyzed at 900-1400℃. Carbon nanotubes were formed in the SiCN matrix through the catalysis of Ni.

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Carbon nanotubes could improve ε′ values. The SiCN matrix could reduce agglomeration and oxidation of Ni nanoparticles.

The PDCs-SiCN(Ni) pyrolyzed at 1200 ℃ exhibited the best wave absorption

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properties.