Glass-Free CuMoO4 Ceramic with Excellent Dielectric and Thermal

Research Article pubs.acs.org/journal/ascecg

Glass-Free CuMoO4 Ceramic with Excellent Dielectric and Thermal Properties for Ultralow Temperature Cofired Ceramic Applications Nina Joseph,* Jobin Varghese, Tuomo Siponkoski, Merja Teirikangas, Mailadil Thomas Sebastian, and Heli Jantunen Microelectronics Research Unit, Faculty of Information Technology and Electrical Engineering, University of Oulu, P.O. box 4500, FI-90014 Oulu, Finland S Supporting Information *

ABSTRACT: A new glass-free low temperature sinterable CuMoO4 ceramic was prepared by a solid state ceramic route. The structural, microstructural, electron dispersive spectrum, and X-ray photoelectron spectroscopy analysis revealed the quality of the material synthesized. The CuMoO4 ceramic sintered at 650 °C exhibits densification of 96% and low coefficient of thermal expansion (CTE) of 4.6 ppm/°C in the temperature range of 25−500 °C. It has relative permittivity (εr) of 7.9, quality factor (Qf) of 53 000 GHz, and temperature coefficient of resonant frequency (τf) of −36 ppm/°C (25−85 °C) at 12.7 GHz. The sintered ceramic also shows εr of 11 and low dielectric loss (tan δ) of 2.7 × 10−4 at the frequency of 1 MHz. The full width half-maximum (fwhm) of A1g Raman mode of CuMoO4 ceramic at different sintering temperatures correlate well with the Qf values. The low sintering temperature, low relative permittivity, high-quality factor, and matching coefficient of thermal expansion to that of Si make CuMoO4 a suitable candidate for ultralow temperature cofired ceramic (ULTCC) applications. KEYWORDS: ULTCC, XRD, XPS, CTE, Raman spectrum, Microwave dielectric properties

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INTRODUCTION The explosive growth of traffic in wireless communication demands fifth generation networks which can operate in the millimeter wave frequency range. The advancing modern communication industry is searching for novel microwave dielectric materials with low sintering temperature, ultralow dielectric loss (speed and selectivity), a low or matching coefficient of thermal expansion, and appropriate dielectric permittivity (low εr for increase the signal speed and high εr for miniaturization).1,2 It also requires the integration of passive components such as inductors, resistors, capacitors, and resonators into the substrate to form the integrated circuits. Recently, considerable attention has been paid to low temperature cofired ceramics (LTCC) technology enabling multilayer microwave devices with excellent dielectric properties and low melting point metal electrode cofiring. Low sintering temperature also has an additional benefit of energy saving and low cost. There are several reports on materials with attractive microwave dielectric properties.3−9 The addition of sintering aids such as low melting glasses or oxides is the traditional method to lower the sintering temperature,10 but it usually lowers the quality factor of the dielectric ceramics. In recent years, dielectric ceramics with low sintering temperatures less than 700 °C and cofireable with Al electrode have aroused much attention. Hence, it paves the way to the ultralow temperature cofired ceramic technology (ULTCC).11 © 2016 American Chemical Society

Glass free dielectric ceramics with ultralow sintering temperature, and good dielectric properties suitable for electronics applications have gained much consideration. A series of microwave ceramics with ultralow firing temperature having low (5−20), medium (20−40), and high (>40) permittivity have been reported.2 Most of these materials belongs to the molybdate, tellurate, and vanadate systems. Many of the molybdates such as Na2MoO4, LiKSm2(MoO4)4, LiBiMoO5, Bi 2 Mo 3 O 12 , Bi 2 Mo 2 O 9 , PbMoO 4 , (KBi) 0.5 MoO 4 , (AgBi)0.5MoO4, (NaBi)0.5MoO4, 0.1(AgBi)0.5MoO4−0.9BiVO4, [(Li0.5Bi0.5)0.098Bi0.902][Mo0.098V0.902]O4, etc. have low sintering temperature in the range of 600−700 °C. These molybdates exhibit εr, Qf, and τf in the range of 4−80, 5000−43000 GHz, and +6 to −215 ppm/°C, respectively.2,11−18 MOO2 was reported to have promising applications in catalysis, sensing, electrochromic displays, recording media, electrochemical supercapacitors and lithium ion batteries.19,20 Among the molybdates, CuMoO4 was reported to exist in two distinct allotropic forms α and γ and possess thermochromic and piezochromic properties. The bright green α phase is stable at high temperature/low pressure, and its structure is composed of [CuO5] polyhedra, [CuO6] polyhedra, and [MoO4] Received: July 5, 2016 Revised: August 25, 2016 Published: August 31, 2016 5632

DOI: 10.1021/acssuschemeng.6b01537 ACS Sustainable Chem. Eng. 2016, 4, 5632−5639

Research Article

ACS Sustainable Chemistry & Engineering

The dielectric measurement in the frequency range of 100 Hz to 1 MHz was performed by Precision LCR meter (Agilent 4284A, Precision LCR Meter, USA) using cylindrical discs of diameter 10 mm and thickness 1.5 mm. The Raman spectra of the ceramic were measured with signals excited by a 488 nm Ar+ laser using spectrometer (LabRam HR800, Horiba Jobin-Yvon, Villeneuved’Arcy, France).

tetrahedra. On the other hand, low temperature/high pressure γ form is reddish brown in color with structure composed of [CuO6] and [MoO6] octahedra. Due to the structural rearrangement, the CuMoO4 displays a distinct reversible change in color near the phase transition at around 200 K at ambient pressure and at room temperature for a pressure of 250 MPa21−27 making it technologically interesting. These chromic materials find application as user-friendly temperature and pressure indicators especially in safety improvement, medical, shock detector, and packaging.23,25−27 However, the microwave dielectric properties of CuMoO4 has not been reported yet. In the present paper, we report the low sintering temperature CuMoO4 with attractive dielectric and thermal properties suitable for ULTCC applications. Hence, CuMoO4 ceramics open up the possibility to explore a broad range of new applications.

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RESULTS AND DISCUSSION XRD patterns of the CMO ceramic calcined at 550 °C, sintered at 650 °C and cofired with 50 wt % Al at 650 °C are shown in Figure 1. The X-ray diffraction peaks of CMO ceramic match

EXPERIMENTAL SECTION

CuMoO4 (CMO) was prepared by solid state route from high purity oxides. Stoichiometric amounts of reagent grade starting materials of CuO and MoO3 (>99%, Alfa Aesar) were weighed and ball milled for 24 h with yttria-stabilized zirconia (YSZ) balls in absolute ethanol medium. The resulting mixture was dried and calcined at 550 °C for 12 h. The calcined powder was again ball milled for 16 h to obtain powder with uniform particle size. The obtained powders were pressed into cylindrical disks (diameter 10 mm and thickness 5 mm) using 5 wt % of PVA (poly(vinyl alcohol)) as a binder with a pressure of 100 MPa for microwave measurements. Green ceramic pellets were sintered in the temperature range of 600−700 °C. The crystal structure of the specimen was analyzed by X-ray diffractometer (D8, Bruker, Billerica, MA) using Cu Kα radiation. Thermogravimetric (TG) and differential scanning calorimetric (DSC) analysis were carried out using TGA/DTA (NETZSCH, STA 499 F3 Jupiter, Germany) at a heating rate of 2 °C/min under air atmosphere. The bulk densities of the sintered samples were measured by Archimedes method. The microstructure analysis of the ceramic was performed using scanning electron microscopy (FESEM, ZEISS Ultra Plus, Germany). Thermo Fisher Scientific ESCALAB 250 Xi using the Mg Kα X-ray source was used for XPS analysis. Reference energies of Au 4f5/2 (83.9 ± 0.1 eV) and Cu 2p3/2 (932.7 ± 0.1 eV) were used for calibrating the spectrometer. The take-off angle (angle between the surface and the analyzer) was kept at 90° for the measurement. The binding energy of 285.0 eV is assigned to the C 1s peak corresponding to the surface contamination and was used as an internal reference for correction of charging effects. The coefficient of thermal expansion (CTE) was investigated in the temperature range of 25−500 °C with cylindrical samples of dimensions 8 mm × 15 mm using dilatometer (NETZSCH, DIL 402 PC/4, Germany) at a heating rate of 5 °C/min. The εr, Qf, and τf were measured using Hakki Coleman and cavity method connected to a vector network analyzer (10 MHz-20 GHz, Rohde & Schwarz, ZVB20, Germany) and temperature chamber (SU261, ESPEC Corp, Japan) in the temperature range of 25−85 °C. The τf is calculated using eq 1,28 and temperature coefficient of relative permittivity (τε), by eq 2.29

τf =

f85 − f25 f25 (85 − 25)

Figure 1. X- ray diffraction pattern of CMO calcined at 550 °C, sintered at 650 °C and cofired with 50 wt % Al at 650 °C. (inset) Schematic crystal structure of CMO.

with the ICDD file card no. 073-0488 and confirm that the synthesized and sintered powder is single phase with triclinic structure. All peaks are indexed and belong to space group P1̅ with unit cell parameters a = 9.903 Å, b = 6.783 Å, c = 8.359 Å, α = 101.08, β = 96.88, γ = 107.05, and V = 517.44 Å3. It is evident from the XRD pattern that the CMO ceramic crystallizes in α phase and schematic crystal structure is shown in the inset of Figure 1. Besides the peaks of CMO and Al, no additional peaks were observed in the XRD of CMO cofired with 50 wt % of Al at 650 °C implying that Al could be used as electrode material. TG/DSC/DDSC heating and cooling curve of CMO calcined at 550 °C is depicted in Figure 2. Thermogravimetric measurements show that no weight loss is observed up to a temperature of 700 °C which indicate that CMO is thermally stable up to 700 °C. The DSC and DDSC curve indicate the stability of CMO α phase throughout the heating and cooling cycle in the measured temperature range of 25−700 °C. The densification of CMO as a function of sintering temperature is shown in Figure 3. Relative density is found to increase with sintering temperature and reaches a saturated value of 96% at 650 °C. A slight decrease in the densification is observed with further increase in sintering temperature, which

10−6 ppm/°C

τε = − 2(τf + αL)ppm/°C

(1) (2)

where αL is the linear thermal expansion coefficient of the dielectric sample. Porosity corrected relative permittivity is calculated using Bosman and Havinga’s correction30 for relative permittivity shown in eq 3, where P represents porosity of the dielectric sample εcorrected = εmeasured(1 + 1.5P)

(3) 5633


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areas of the microstructure and is shown in Figure 4c. The EDS spectrum analysis result is shown in Table 1 in the Supporting Information. It indicates that elemental composition in the different selected spectral regions is almost constant in atomic weight percent. The backscattered electron images (BSE) of cofired sample with 50 wt % Al sintered at 650 °C is shown in Figure 4d. The light colored grains belong to the CMO phase whereas the dark ones are pure aluminum particles, which further confirms the chemical compatibility between CMO and Al. The oxidation state and chemical composition on the surface of prepared CMO ceramic are analyzed by XPS technique. A qualitative and quantitative analysis of the CMO ceramic sintered at 650 °C within the surface layer of about 50 Å is extracted from the spectrum. The survey spectrum of the CMO ceramic is shown in Figure 5a. Besides the expected Cu 2p, Mo 3d, O 1s peaks, a C 1s peak is also observed. The C 1s peak does not affect the interpretation of the present results and in fact, it is used for binding energy calibration by setting its binding energy at 284.8 eV for sample charging correction.32,33 Figure 1 in the Supporting Information shows the high resolution C 1s spectrum. Figure 5b depicts the high resolution spectrum of Cu 2p. Spin−orbital splitting components of 2P3/2 and 2p1/2 split by about 19.79 eV with fwhm of 3.1 eV each. Strong satellite peaks of Cu2+ in the high resolution spectrum indicate the existence of Cu in Cu2+ oxidation state in the sintered CMO ceramic.34 It is reported that Auger line of L3M45M45 (1 G) [kinetic energy of 917.7 eV] belongs to Cu2+ oxidation state.35 The high resolution Cu Auger spectrum of CMO ceramic is depicted as Figure 2 in the Supporting Information and further confirms the 2+ oxidation state of Cu. Table 1 presents the Cu 2p fitted binding energy and atomic weight percent. Figure 5c shows the high resolution spectrum of Mo 3d with spin−orbital splitting 3d5/2 and 3d3/2 having an orbital split of about 3.16 eV and fwhm of 1.65 and 1.19 eV respectively. The Mo 3d fitted binding energy and elemental composition are also given in the Table 1. The Mo 3d scan suggests that Mo in CMO belongs to the 6+ oxidation state.36 Core-level spectrum of O 1s and its curve fitting for CMO ceramic are shown in Figure 5d. This O 1s photoelectron peak provides information on the oxide ion in the sintered CMO with different chemical bonding. A well-resolved peak at 530.15 eV fitted with atomic weight percent of 48.5 related with the bridging oxygen atoms. The peak associated with O 1s shows good agreement with reported values.37,38 X-ray diffraction, TG/DSC, microstructure, EDS, and XPS results reveal the thermal and structural stability of prepared CMO ceramic. The linear thermal expansion curve of CMO sintered at 650 °C in the temperature range of 25−500 °C is given in Figure 6. The thermal expansion data shows a linear variation with increase in temperature and has an average CTE of 4.6 ppm/°C close to silicon semiconductor (4 ppm/°C) which gives an additional advantage to the CMO for device level integration.39,40 The CMO ceramic exhibits almost uniform CTE at both heating and cooling cycles over the measured temperature range. The sintering temperature of CMO ceramic is also optimized using best of microwave dielectric properties. The εr and Qf measured at 12.7 GHz for CMO ceramic as a function of sintering temperature is shown in Figure 7. These values show a similar trend to that of relative density variation shown in Figure 3. It indicates that densification plays an important role

Figure 2. TG/DSC/DDSC curve of CMO calcined at 550 °C.

Figure 3. Variation of densification with sintering temperature of CMO.

may be due to the irregular grain growth.31 The results indicate that the CMO ceramic can be well densified at 650 °C. The surface and fractured SEM images of the CMO sintered at 650 °C (Figure 4a and b) show that the ceramic exhibit good uniformity in grain size with high densification being in good agreement with the density measured. EDS analysis is conducted on CMO sintered at 650 °C by selecting different

Figure 4. Microstructure of the (a) surface, (b and c) fractured surface of CMO, and (d) back scattered electron images of cofired sample with 50 wt % Al sintered at 650 °C. 5634


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Figure 5. XPS (a) survey spectrum and high resolution spectrum of (b) Cu 2p, (c) Mo 3d, and (d) O 1s of CMO ceramic sintered at 650 °C.

Table 1. Binding Energy and Atomic Weight Percent of Cu 2p, Mo 3d, and O 1s Cu 2p3/2

Cu 2p1/2

Mo 3d5/2

Mo 3d3/2

O 1s

sample

BE (eV)

atomic wt %

BE (eV)

atomic wt %

BE (eV)

atomic wt %

BE (eV)

atomic wt %

BE (eV)

atomic wt %

CMO

934.91

7.7

954.70

9.0

232.06

4.0

235.22

6.5

530.15

48.5

Figure 7. Variation of εr and Qf of CMO as a function of sintering temperature at frequency 12.7 GHz.

Figure 6. Thermal expansion curve of heating and cooling cycle measured in the temperature range of 25−500 °C of CMO ceramic sintered at 650 °C.

ceramic is also an important factor for practical applications. Optimized CMO ceramic shows τf of −36 ppm/°C calculated using eq 1 and τε of 63 ppm/°C using eq 2 at the microwave frequency range in the temperature range of 25−85 °C. Figure 8 shows the frequency dependence of the εr and tan δ of optimized CMO ceramic in the frequency range of 102−106 Hz. The value of εr gradually decreases with increase in frequency and remains almost stabilized at high frequency range. The reduction of relative permittivity with increasing frequency is previously reported by many researchers and is a

in governing the dielectric properties. The CMO ceramic sintered at 650 °C with the highest densification of 96% shows εr of 7.9 and Qf of 53 000 GHz at the measured frequency. The porosity corrected relative permittivity of this ceramic is 8.4. The CMO ceramic sintered at 650 °C exhibit best microwave dielectric properties and hence optimized for further microwave and low frequency dielectric studies. In addition to dielectric properties, temperature stability of the dielectric properties of 5635


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various temperatures (625, 650, 675, and 700 °C) over the Raman shift of 50−1000 cm−1. The [MoO4] tetrahedra molecular groups with strong covalent bond are peculiar to the molybdates and exhibit active modes. It has a weak coupling with Cu2+ cations and hence the vibrational modes obtained are low. The CuO is reported to have three Raman active modes (Ag + 2Bg) obtained by a factor group analysis based on the results achieved by Rousseau et al.46 The mode around 300 cm−1 is attributed to Ag while those around 375 and 675 cm−1 are bending vibrations correspond to Bg modes of CuO observed in the CMO Raman spectra.47−49 On the other hand, orthorhombic unit cell of molybdates has four formula units and belong to space group D2h6 according to structural symmetry. It has 24 active Raman modes (8Ag + 8Blg + 4B2g + 4B3g) based on group theory analysis.50 The modes around 1000−600 cm−1 and 400−200 cm−1 correspond respectively to the stretching and bending vibrations in MoO4 tetrahedra in CMO.51,52 The vibrations below 200 cm−1 are considered as attributed to lattice modes. There are three translational degrees of freedom for terminal oxygen atoms (O−Mo). The observed high frequency bands in the range 885−1000 cm−1 are due to the stretching modes of the (O−Mo) terminal.50,53 The stretching vibration modes of MoO4 tetrahedra are observed at around 804, 840, 937, 970 cm−1.51,52,54 The strongly polarized Raman-active peak at 970 cm−1 is attributed to the vibration along the zigzag rows. The low intensity modes in the range 258−284 cm−1 are the deformation modes of the O−Mo bonds. According to Barraclough et al., the band around 885 cm −1 corresponds to Mo−O (3, 3′) vibration.55 The two connected Mo−O−Mo bonds are formed as a result of bridging oxygens (OMo2) and its stretching occurs in the range of 840−700 cm−1. The modes in the 230−190 cm−1 correspond to its deformation. The in plane modes of (O− Mo3) units are observed in the region of 700−468 cm−1 while the out of plane modes in the range of 400−335 cm−1. The modes corresponding to (O2M2)n polyhedron are found at around 115 and 175 cm−1 and are having low intensity. The mode at 136 cm−1 attributes to the vibration along (001) direction predominantly.50 The symmetry and assignment of the Raman modes of CMO are given in Table 2. The narrow peaks at both high and low frequency range of Raman spectra of CMO indicate that the synthesized material is

Figure 8. Variation of (a) εr and (b) tan δ of CMO with frequency in the range of 102−106 Hz (inset) tan δ of CMO with frequency in the range of 104−106 Hz.

normal dielectric behavior.28,41 The CMO ceramic exhibits εr in the range of 11.7−11.0 in the measured frequency range. The dielectric loss also follows a similar trend and is rather high at low frequency and falls quickly with increasing frequency. It may be due to the inability of the dipoles to follow the high frequency of the applied field.28,42 The value of tan δ varies from 0.2 to 2.7 × 10−4 in the measured frequency range. The low dielectric loss value of CMO at high frequency is more evident from the inset figure of Figure 8. The CMO ceramic exhibit low dielectric loss of 2.7 × 10−4 and porosity corrected εr = 11.6 at a frequency of 1 MHz. The results are in good agreement with the microwave dielectric properties. Microwave dielectric losses in ceramics may arise from a combination of intrinsic and extrinsic factors. Intrinsic losses primarily depend on harmonic interactions of the electric field with the crystal phonons.43 Nevertheless, extrinsic losses are associated with microstructural imperfections, such as porosity, secondary phases, grain sizes, oxygen vacancies and are found to affect the dielectric losses at microwave frequencies adversely.44,45 To understand the effect of intrinsic loss of CMO, the variation of Raman spectrum of CMO with different sintering temperature is studied. Figure 9a presents the room temperature Raman spectra of CMO ceramics sintered at

Table 2. Raman Spectra of CMO Ceramica

Figure 9. (a) Raman spectra, (b) Qf and A1g fwhm, and (c) correlation of A1g fwhm and Qf value of CMO ceramic sintered at 625−700 °C.

a

5636

Raman modes observed

symmetry [assignment]

ref

970 840 701 675 473 372 335 300 260 230 175 136 115 77

A1g, B1g [ν(OMo)] B1g [ν(OMo2) ] B3g [ν(OMo3) ] Bg [CuO) ] B1g [ν(OMo3) ] Bg [CuO) ] Ag [δ(OMo3)] Ag [CuO)] B2g [δ(OMo)] Ag [δ(OMo2) ] Ag [δ(O2Mo2)n] B2g other deformation modes lattice modes Ag−Mo−Mo mode

50,54 50,54 50,54 47,49 50,54 47,49 50,54 47,49 50,54 50,54 50,54 50,54 50 50

Frequencies in inverse centimeters. DOI: 10.1021/acssuschemeng.6b01537 ACS Sustainable Chem. Eng. 2016, 4, 5632−5639

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ACS Sustainable Chemistry & Engineering of good quality and is confirmed by XRD, EDS and XPS analysis.56 Among the vibration modes, the stretch mode (A1g with wavenumber around 970 cm−1) of the oxygen octahedra has the strongest polarity as well as strong intensity and hence exert strong influence on the microwave dielectric properties.43,57 Figure 9b shows the relationship between the Qf and fwhm of A1g mode of CMO sintered at different temperatures. The fwhm is obtained by fitting the A1g mode with Lorentz function. The effect of sintering on the ordering of ceramic is evident by analyzing the fwhm of active mode in Raman spectra. This Raman line exhibits no shift while the fwhm of CMO ceramic varies with sintering temperature. The fwhm decreases with increase in sintering temperature up to 650 °C and a further increase in sintering temperature results in a slight increase. On the other hand, the Qf value follows the reverse trend and it increases linearly with the decrease in fwhm, which is evident from Figure 9c. The CMO ceramic sintered at 650 °C exhibit minimum fwhm of A1g mode which indicate high degree of ordering and low phonon damping which in turn leads to the higher value of Qf.58 The decrease of fwhm denotes the weakening of the coherence and damping behavior of A1g stretching vibration and hence results in the reduction of unharmonic vibrations which in turn relates to low dielectric loss. It eventually leads to the increase in intrinsic Qf value inversely.58−60 Hence, CMO ceramic could be applied to substrates for high-speed devices due to the low permittivity for reducing the signal delay time and the high quality factors (Qf) for frequency selectivity.61 In addition to this, the low sintering temperature of 650 °C makes it a possible candidate for ULTCC applications. All these excellent dielectric and thermal properties with good densification at a low sintering temperature of 650 °C combined with the reported thermochromic and piezochromic nature of CuMoO4 ceramic make it an attractive candidate for ULTCC smart substrate and packaging applications.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (N.J.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS

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REFERENCES

The authors are thankful to European Research Council Project No: 24001893 for financial support. The authors also acknowledge Mr. Santtu Heinilehto (Application Engineer) for XPS and Mr. Pekka Moilanen for Raman spectroscopy measurements.

(1) Sebastian, M. T.; Ubic, R.; Jantunen, H. Low-Loss Dielectric Ceramic Materials and their Properties. Int. Mater. Rev. 2015, 60, 392− 412. (2) Sebastian, M. T.; Wang, H.; Jantunen, H. Low Temperature Cofired Ceramics with Ultralow Sintering Temperature: A Review. Curr. Opin. Solid State Mater. Sci. 2016, 20, 151. (3) Wang, Y.; Zuo, R. A Novel Low-Temperature Fired Microwave Dielectric Ceramic BaMg2V2O8 with Ultra-Low Loss. J. Eur. Ceram. Soc. 2016, 36, 247−251. (4) Alford, N. M.; Penn, S. J. Sintered Alumina with Low Dielectric Loss. J. Appl. Phys. 1996, 80, 5895−5898. (5) Kim, J. C.; Kim, M. H.; Lim, J. B.; Nahm, S.; Paik, J. H.; Kim, J. H. Synthesis and Microwave Dielectric Properties of Re3Ga5O12(Re: Nd, Sm,Eu, Dy, Yb, and Y) Ceramics. J. Am. Ceram. Soc. 2007, 90, 641−644. (6) Varghese, J.; Siponkoski, T.; Teirikangas, M.; Sebastian, M. T.; Uusimäki, A.; Jantunen, H. Structural, Dielectric, and Thermal Properties of Pb Free Molybdate Based Ultralow Temperature Glass. ACS Sustainable Chem. Eng. 2016, 4, 3897−3904. (7) Zhou, D.; Guo, D.; Li, W. B.; Pang, L. X.; Yao, X.; Wang, D. W.; Reaney, I. M. Novel Temperature Stable High-εr Microwave Dielectrics in the Bi2O3−TiO2−V2O5 system. J. Mater. Chem. C 2016, 4, 5357−5362. (8) Zhou, D.; Randall, C. A.; Pang, L. X.; Wang, H.; Guo, J.; Zhang, G. Q.; Wu, X. G.; Shui, L.; Yao, X. Microwave Delectric properties of Li2WO4 Ceramic with Ultra-Low Sintering Temperature. J. Am. Ceram. Soc. 2011, 94, 348−350. (9) Varghese, J.; Joseph, T.; Sebastian, M. T.; et al. Crystal Structure and Microwave Dielectric Properties of LaLuO3 Ceramics. J. Am. Ceram. Soc. 2010, 93, 2960−2963. (10) Zhou, D.; Pang, L.-X.; Xie, H.-D.; Guo, J.; He, B.; Qi, Z.-M.; Shao, T.; Yao, X.; Randall, C. A. Crystal Structure and Microwave Dielectric Properties of an ULTCC (AgBi)0.5WO4 Ceramic. Eur. J. Inorg. Chem. 2014, 2014, 296−301. (11) Zhou, D.; Randall, C. A.; Wang, H.; Pang, L.-X.; Yao, X. Ultra low firing high k sheelite structures based on ((Li0.5Bi0.5)xBi1‑x) (MoxV1‑x)O4 microwave dielectric ceramics. J. Am. Ceram. Soc. 2010, 93, 2147−2150. (12) Zhang, G.; Wang, H.; Guo, J.; He, L.; Wei, D.; Yuan, Q. UltraLow Sintering Temperature Microwave Dielectric Ceramics Based on Na2O-MoO3 Binary System. J. Am. Ceram. Soc. 2015, 98, 528−533. (13) Zhai, X.-L.; Zheng, X.; Xi, H.-H.; Li, W.-B.; Han, J.; Zhou, D. Microwave Dielectric Properties of LiKSm2(MoO4)4 Ceramics with Ultralow Sintering Temperatures. J. Am. Ceram. Soc. 2015, 98, 2716− 2719. (14) Zhou, D.; Randall, C. A.; Wang, H.; Pang, L.-X.; Yao, X. Microwave Dielectric Ceramics in Li2O−Bi2O3−MoO3 System with

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CONCLUSION CuMoO4 ceramic was prepared by solid state ceramic route. The XRD, microstructural, EDS, and XPS analysis indicate the phase purity and quality of the synthesized ceramic. The ceramic exhibits densification of 96% after sintering at 650 °C and also low CTE (4.6 ppm/°C) in the temperature range of 25−500 °C feasible for Si device integration. The ceramic sintered at 650 °C has εr = 7.9 and Qf = 53 000 GHz at a frequency of 12.7 GHz. The τf and τε in the temperature range of 25−85 °C is −36 and 63 ppm/°C, respectively. At 1 MHz the measured εr and tan δ values were 11 and 2.7 × 10−4, respectively. The relationship between structure and good microwave dielectric properties of CMO sintered at 650 °C is clearly understood by analyzing the fwhm of the stretch mode A1g (wavenumber around 970 cm−1) of Raman spectrum. Low sintering temperature, good densification, low CTE and dielectric constant along with high Qf make CuMoO4 ceramic a potential candidate for ULTCC applications.

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Table S1. EDS spectrum analysis table. Figure S2. High resolution C 1s peak of sintered CMO. Figure S3. Auger peak of copper of sintered CMO (PDF)

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b01537. 5637


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Glass-Free CuMoO4 Ceramic with Excellent Dielectric and Thermal

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