Next Article in Journal
A Micro-Power Generator Based on Two Piezoelectric MFC Films
Next Article in Special Issue
Surface Acoustic Wave-Based Flexible Piezocomposite Strain Sensor
Previous Article in Journal
Effect of Hot Working Processes on Microstructure and Mechanical Properties of Pipeline Steel
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Crystal Structure and Electrical Characteristics of (0.965)(Li0.03(Na0.5K0.5)0.97)(Nb1−xSbx)O3−0.035(Bi0.5Na0.5)0.9(Sr)0.1ZrO3 Ceramics Doped with CuO, B2O3, and ZnO

Department of Electrical Engineering, Semyung University, Jecheon 390-711, Korea
*
Author to whom correspondence should be addressed.
Submission received: 24 June 2021 / Revised: 21 July 2021 / Accepted: 21 July 2021 / Published: 24 July 2021
(This article belongs to the Special Issue Piezoelectric Sensors Application)

Abstract

:
Recently, the need has arisen to enhance the piezoelectric properties and temperature stability of (Na,K)NbO3 system ceramics. The (0.965)(Li0.03(Na0.5K0.5)0.97)(Nb1−xSbx)O3−0.035 (Bi0.5Na0.5)0.9(Sr)0.1ZrO3 ceramics were newly manufactured using the sintering aids of CuO, B2O3, and ZnO as a function of antimony substitution, and the their crystal structure and electrical characteristics were analyzed. The grain size was apparently refined as the amount of antimony increased. The dielectric constant was enhanced and Curie temperature was decreased due to the content of the antimony substitution. The x = 0.07 sample sintered at 1060 °C presented the best electrical characteristics, which were bulk density = 4.488 g/cm3, piezoelectric constant d33 = 330 pC/N, electromechanical coupling factor kp = 0.427, mechanical coupling factor Qm = 61, and dielectric constant εr = 2521. We believe that the x = 0.07 sample is the best material for piezoelectric speakers.

1. Introduction

In recent years, lead zirconate titanate ceramics have been extensively utilized in application devices such as piezoelectric actuator, ultrasonic motors, piezoelectric transformer, and ultrasonic cutters [1,2,3,4,5]. In particular, various multi-structured piezoelectric ceramics were investigated for the application of piezoelectric speaker capable of being used in smart phone speaker. It is well known that (Bi0.5Na0.5)ZrO3 addition could simultaneously increase TR-O(Rhombohedral-Orthorhombic transition temperature) and decrease TO-T (Orthorhombic-tetragonal transition temperature) of KNN ((K,Na)NbO3) system ceramics. Accordingly, a rhombohedral-tetragonal (R-T) coexistence phase can appear. Because this R-T phase transition may act similarly to the classical morphotropic phase boundary (MPB) observed in PZT ceramics, the higher d33 may be expected [6,7,8,9,10,11,12,13]. Therefore, in compositionally modified KNN ceramics, increased dielectric and piezoelectric properties can be obtained by forming the R-T Polymorphic phase transition (PPT) near room temperature. It is well-known that the MPB region with tetragonal and rhombohedral structure can enhance the piezoelectricity of the PZT ceramics, owing to the involvement of the more polarization states [14]. Accordingly, piezoelectric devices have mainly utilized the ceramics close to the tetragonal and rhombohedral phase boundary.
The predominant KNN system ceramics substituted with (Ba,Na)ZrO3 were developed due to the coexistence of tetragonal and rhombohedral phases [15].
The KNN system ceramics have sintered at a high sintering temperature of more than 1100 °C. Accordingly, the ceramics can induce compositional fluctuation owing to rapid volatilization of alkali elements at above 1100 °C [16]. Moreover, cheap Ag rich-Pd inner electrode in the multilayer structured ceramics should be used for price competitiveness. CuO, B2O3, and ZnO can also be utilized as the sintering aids in order to decrease the sintering temperature of the KNN ceramics. A low temperature sintering process for the ceramics can be achieved using the liquid phase formation owing to their lower melting point. Antimony (Sb) substituted with the KNN system can also decrease TO-T and increase TR-O [17,18]. The increase of piezoelectric ceramic strain (S) according to the electric field (E) can enhance the sound pressure level of the piezoelectric speaker (S = d33E). Accordingly, with the aim of enhancing the piezoelectric constant d33, physical properties, and temperature stability of (Na,K)NbO3 ceramics, (0.965)(Li0.03(Na0.5K0.5)0.97)
(Nb1−xSbx)O30.035(Bi0.5Na0.5)0.9(Sr)0.1ZrO3 ceramics were newly manufactured using the sintering aids of CuO, B2O3, and ZnO as a function of antimony substitution. Here, we have selected the x = 0.04–0.08 composition ceramics to focus on the composition of R-T MPB regions, and their crystal structure and electrical characteristics were investigated for piezoelectric speaker applications.

2. Experiments

In these experiments, the following composition samples were fabricated according to the following traditional manufacturing method [19];
(0.965)(Li0.03(Na0.5K0.5)0.97)(Nb1−xSbx)O3−0.035(Bi0.5Na0.5)0.9(Sr)0.1ZrO3 + sintering aids (0.1 wt% B2O3 + 0.2 wt% ZnO + 0.2 wt% CuO) (from x = 0.04 to 0.08)
All raw materials, including K2CO3, Li2CO3, Na2CO3, Sb2O5, SrCO3, Bi2O3, and ZrO2, were ball-milled for 24 h, and the powders were dried and calcined at 850 °C for 6 h. After performing calcining, CuO, B2O3, and ZnO as the sintering aids were added, and then, a PVA as binder was added to the dried powders. The powders including the binder were formed by a pressure of 17 MPa using a mold with a diameter of 17 mm, and then the ceramics formed were sintered at 1060 °C for 10 h. The density was measured using the Archimedes method. For the purpose of measuring the electrical characteristics, all samples lapped to thickness (= 1.0 mm) were electro-deposited using Ag paste. In order to measure the piezoelectric and dielectric characteristics, the specimens were polished to 1 mm thickness and then electrodeposited with Ag paste. Poling of the samples was carried out at 120 °C in a silicon oil bath by applying DC fields of 3 kV/mm for 30 min. To investigate the dielectric properties, capacitance was measured at 1 kHz (standard frequency) using an LCR meter (ANDO AG-4034) (Rancho Cordova, CA, USA) and the dielectric constant of the non-poled sample was calculated. Piezoelectric constants were obtained using a d33 meter (APC-90-2030, 46 Heckman Gap Road, Mill Hall, PA 17751, USA). To investigate the piezoelectric properties, the resonant and anti-resonant frequencies were measured using an Impedance Analyzer (Agilent 4294A, 1150 Raymond Avenue SW Renton, WA, USA) according to IRE standard, and then the electromechanical coupling factor kp and mechanical quality factor Qm were calculated [20].
To determine the crystal structure of the specimen, the X-ray diffraction meter (XRD: Rigaku, D/MAX-2500H) was irradiated at a diffraction angle 2θ between 20° and 80° by a powder method using a CuKα line having a wavelength of λ = 1.5406 Å. The microstructure of the specimen was observed at 3000 magnification with the aids of a scanning electron microscope (SEM: Model Hitachi, S-2400) [17,18].

3. Results and Discussion

The microstructure of samples with antimony are shown in Figure 1. The surface grain size of the samples were significantly reduced with the increase of the antimony. This is explained by the fact that the Sb5+ ion can reduce the average grain size with the increase of antimony [19,20]. As shown in Figure 2, the grain size was refined as the amount of Sb5+ further increased from 5.2 μm (x = 0.04) to 2.3 μm (x = 0.08) [20]. According to the decrease of grain size, densification of the crystal microstructure was also performed. Sintering aids CuO, B2O3, and ZnO may promote the chemical reaction of ceramic particles owing to a liquid phase formation and then can enhance the ceramic densification.
The X-ray diffraction (XRD) pattern with the antimony of samples fired at 1060 °C for 10 h are shown in Figure 3. All off the samples exhibit pure perovskite phase, and no secondary phases were investigated. The ceramic samples from x = 0.04 to x = 0.07 possess coexistence of a rombohedral-tetragonal (R-T) shape, which is indicated by the tetragonal (002) and (200), along with the rhombohedral (200) peak, as shown in Figure 3b. Here, the intensity of the tetragonal (002) peak was slowly weakened, and the rhombohedral (200) peak evidently appeared in association with the increase in antimony substitution. When x = 0.07, the piezoelectricity of the samples was greatly enhanced due to the increase of the coexistence ratio of a rombohedral-tetragonal (R-T) shape.
When the antimony x = 0.08, the rhombohedral (200) peak was appeared to be large while the tetragonal (002) peak was weakened.
The density of the samples with the antimony are shown in Figure 4. With the increased antimony content, the density of samples was slowly enhanced due to the densification of the crystal microstructure up to x = 0.07. In the composition ceramics above x = 0.07, the density was decreased due to over substitution to the KNN system. This was also because of the liquid phase firing effects of sintering aids (CuO melting point; 1020 °C, B2O3 melting point; 460 °C).
The kP with the antimony are shown in Figure 5, and also the Qm of the samples with the antimony are shown in Figure 6. The kp increased with increasing antimony, when antimony was increased up to x = 0.07 (that is, kp = 42.7%), and the kp decreased with further increase above x = 0.07. The results can also illustrated the fact that the densification of the samples decreases due to the over addition of antimony, and that Qm slowly reduced with increasing antimony content. When the content of antimony was x = 0.04, the maximum of Qm = 80 was obtained. This perhaps indicates that the Sb5+ ion can enter into the B-sites of Zr4+ except for Nb5+ due to the softener effect leading to a decrease in Qm with increasing antimony content.
The dielectric constant εr and piezoelectric constant d33 of samples with the antimony are shown in Figure 7 and Figure 8, respectively. The dielectric constant εr of samples with the antimony increased linearly. After poling the samples as a 3 kV/mm electric field (E), the d33 was measured. The d33 was increased with the content of antimony up to x = 0.07 and then reduced above x = 0.07. In general, in order to increase the sound pressure level of the piezoelectric speaker, the highest d33 is required because the strain (S) is in proportion to the electric field (E). The ceramics with x = 0.07 possessed the best piezoelectricity (d33 = 330 pC/N, εr = 2521) for piezoelectric speaker application. These values were shown to be higher than d33 = 241 pC/N and εr = 1705 in our recently published paper [21,22].
The antimony content can enhance the sinterability of the samples together with the liquid phase formation of CuO and B2O3, resulting in enhancement of d33 and εr. The d33 of x = 0.07 specimen with electric field shown in Figure 9.
As the electric field (E) increased, the piezoelectric constant d33 increased.
When the electric field (E) was 3 kV/mm, the maximum d33 = 330 pC/N was obtained. Thereafter, the piezoelectric constant d33 was decreased due to a micro-cracking phenomenon under over electric field (E) of the specimen.
The dielectric constant temperature dependence of the samples with the antimony are shown in Figure 10. Primary phase transition temperature TR-T slowly increased and also the Curie temperature Tc gradually decreased according to the increase in antimony.
Physical properties of the samples with the amount of antimony are summarized in Table 1.

4. Conclusions

In this experiment, the modified (Na,K,Li)NbO3–(Bi,Ba)ZrO3 ceramics were manufactured using CuO, B2O3, and ZnO as the sintering aids as a function of antimony substitution.
Their crystal structure and electrical characteristics were analyzed as follows:
  • The grain size was refined as the amount of antimony increased.
  • Dielectric constant was enhanced and Curie temperature was decreased due to the content of antimony substitution.
  • With the x = 0.08 specimen, the rhombohedral (200) peak appeared. When the amount of antimony was between x = 0.04 and x = 0.07, the coexistence of the tetragonal and rhombohedral phase apparently appeared.
  • The x = 0.07 sample sintered at 1060 °C presented the best electrical characteristics: bulk density = 4.488 g/cm3, d33 = 330pC/N, kp = 0.427, Qm = 61, and εr = 2521. We believe that the x = 0.07 sample is the best material for piezoelectric speakers.

Author Contributions

Investigation, S.K.; Supersision, J.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This paper was studied by 2017 National Research Foundation of Korea.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Yoo, J. Excellent piezoelectric properties and high Tc in Fe2O3-doped PMW-PNN-PZT ceramics. Ferroelectr. Lett. Sect. 2018, 45, 1–7. [Google Scholar] [CrossRef]
  2. Kim, S.; Yoo, J. PHYSICAL CHARACTERISTICS OF (1-X)(NKL)(NST) O3-X(BA0.90 CA0.1) ZRO3 CERAMICS. Trans. Electr. Electron. Mater. 2019, 20, 426–430. [Google Scholar] [CrossRef]
  3. Cho, S.; Jeong, Y.-H.; Yoo, J. Dielectric and piezoelectric properties of 0.97(Na0.52K0.443Li0.037)(Nb0.96−xSb0.04Tax)O3-0.03(Bi0.5Na0.5)0.9(Sr)0.1ZrO3 ceramics for pizoelectric actuator. Trans. Electr. Electron. Mater. 2019, 20, 328. [Google Scholar] [CrossRef]
  4. Yoo, J. Dielectric and piezoelectric properties of (Na0.52K0.443Li0.037)(Nb0.883Sb0.08Ta0.037)O3 ceramics substituted with (Bi0.5Na0.5)0.9(Sr)0.1ZrO3. Ferroelectrics 2019, 550, 220–227. [Google Scholar] [CrossRef]
  5. Minho, P.; Yoo, J. Piezoelectric and dielectric properties of nonstoichiometric (Na0.5K0.5)0.97(Nb0.90Ta0.1)O3 ceramics doped with MnO2. J. Electron. Mater. 2012, 41, 3095–3099. [Google Scholar]
  6. Zhou, C.; Zhang, J.; Yao, W.; Liu, D.; Su, W. Highly temperature-stable piezoelectric properties of 0.96(K0.48Na0.52)(Nb0.96Sb0.04)O3-0.03BaZrO3-0.01(Bi0.50Na0.50)ZrO3 ceramic in common usage temperature range. Scr. Mater. 2019, 162, 86. [Google Scholar] [CrossRef]
  7. Zhang, B.Y.; Wu, J.G.; Cheng, X.J.; Wang, X.P.; Xiao, D.Q.; Zhu, J.G.; Wang, X.J.; Lou, X.J. Large d33 in (K,Na)(Nb,Ta,Sb)O3-(Bi,Na,K)ZrO3 lead-free ceramics. J. Mater. Chem. A 2014, 2, 4122–4126. [Google Scholar]
  8. Zheng, J.G.; Wu, Q.; Chen, D.; Xiao, Q.; Zhu, J.G. Composition-driven phaseboundary and piezoelectricity in potassium_sodium niobate-based ceramics. ACS Appl. Mater. Interfaces 2015, 7, 20332–20341. [Google Scholar] [CrossRef] [PubMed]
  9. Rubio-Marcos, F.; Lopez-Juarez, R.; Rojas-Hernandez, R.E.; del Campo, A.; Razo-Perez, N.; Fernandez, J.F. Lead-free piezo ceramics: Revealing the role of the rhombohedral-tetragonal phase coexistence in enhancement of the piezoelectric properties. ACS Appl. Mater. Interfaces 2015, 7, 23080–23088. [Google Scholar] [CrossRef]
  10. Tao, H.; Wu, J.G.; Wang, H. Modification of strain and piezoelectricity in (K,Na)NbO3e(Bi,Na)HfO3 lead-free ceramics with high Curie temperature. J. Alloys Compd. 2016, 684, 217–233. [Google Scholar] [CrossRef] [Green Version]
  11. Xu, K.; Li, J.; Lv, X.; Wu, J.G.; Zhang, X.X.; Xiao, D.Q.; Zhu, J.G. Superior piezoelectric properties in potassium sodium niobate lead-free ceramics. Adv. Mater. 2016, 28, 8519–8523. [Google Scholar] [CrossRef]
  12. Wu, B.; Wu, H.J.; Wu, J.G.; Xiao, D.Q.; Zhu, J.G.; Pennycook, S.J. Giant piezoelectricity and high curie temperature in nanostructured alkali niobate lead-free piezo ceramics through phase coexistence. J. Am. Chem. Soc. 2016, 138, 15459. [Google Scholar] [CrossRef]
  13. Xiang, R.; Wu, J. Contribution of Bi0.5Na0.5ZrO3 on phase boundary and piezoelectricityin K0.48Na0.52Nb0.96Sb0.04O3-Bi0.5Na0.5SnO3-xBi0.5Na0.5ZrO3 ternary ceramics ceramics. J. Alloys Compd. 2020, 820, 153411. [Google Scholar]
  14. Gou, Q.; Zhu, J.; Wu, J.; Li, F.; Jiang, L.; Xiao, D. Microstructure and electrical properties of (1-x)K0.5Na0.5NbO3-xBi0.5Na0.5Zr0.85Sn0.15O3 lead-free ceramics. J. Alloys Compd. 2018, 730, 311–317. [Google Scholar] [CrossRef]
  15. Jaffe, B.; Cook, W.R.; Jaffe, H. Piezoelectric Ceramics; Academic Press: Cambridge, MA, USA, 1971. [Google Scholar]
  16. Yoo, J. Effect of sintering temperature on the dielectric and piezoelectric properties of (Na0.525K0.443Li0.037)(Nb0.883Sb0.08Ta0.037)O3 Pb-free ceramics for actuator. Ferroelectrics 2017, 507, 12. [Google Scholar] [CrossRef]
  17. Noh, J.; Yoo, J. Dielectric and piezoelectric properties of KCT added (Li0.02(Na0.56K0.46)0.98(Nb0.81Ta0.15Sb0.04)O3 ceramics. J. Electroceram. 2013, 30, 139–144. [Google Scholar] [CrossRef] [Green Version]
  18. Yoo, J.; Lee, J. The effects of MnO2 addition on the physical properties of Pb(Ni1/3Nb2/3)O3-Pb(Zr,Ti)O3-Pb(Mg1/2W1/2)O3-BiFeO3 ceramics. Crystals 2021, 11, 269. [Google Scholar] [CrossRef]
  19. Zhou, C.; Zhang, J.; Yao, W.; Liu, D.; He, G. Remarkably strong piezoelectricity, rhombohedral-orthorhombic-tetragonal phase coexistence and domain structure of (K,Na)(Nb,Sb)O3-(Bi,Na)ZrO3-BaZrO3 ceramics. J. Alloys Compd. 2020, 820, 153411. [Google Scholar] [CrossRef]
  20. Yoo, J.; Lee, J. Microstructure and piezoelectricity of (Na,K,Li)(Nb,Sb)O3–(Bi,Na)(Sr)ZrO3–BaZrO3 ceramics. Crystals 2020, 10, 868. [Google Scholar] [CrossRef]
  21. Zhang, B.; Wu, J.; Cheng, X.; Wang, X.; Xiao, D.; Zhu, J.; Wang, X.; Lou, X. Lead-free piezoelectrics based on potassium–sodium niobate with giant d33. ACS Appl. Mater. Interfaces 2013, 5, 7718–7725. [Google Scholar] [CrossRef]
  22. Yoo, J.; Lee, Y.W.; Lee, J. Dielectric and piezoelectric properties of 0.965(Na0.5K0.5)0.97Li 0.03(Nb0.96Sb0.04)O3−0.035(Bi0.5Na0.5)0.9(Sr)0.1ZrO3 ceramics with CuO addition. Ferroelectrics 2021, 572, 51. [Google Scholar] [CrossRef]
Figure 1. Scanning electron microscopy (SEM) of samples with the amount of antimony (a) x = 0.04, (b) x = 0.05, (c) x = 0.06, (d) x = 0.07, (e) x = 0.08.
Figure 1. Scanning electron microscopy (SEM) of samples with the amount of antimony (a) x = 0.04, (b) x = 0.05, (c) x = 0.06, (d) x = 0.07, (e) x = 0.08.
Crystals 11 00859 g001
Figure 2. Grain size of samples with the amount of antimony.
Figure 2. Grain size of samples with the amount of antimony.
Crystals 11 00859 g002
Figure 3. X-ray diffraction patterns of samples with the amount of antimony: (a) Wide Range, (b) Narrow Range.
Figure 3. X-ray diffraction patterns of samples with the amount of antimony: (a) Wide Range, (b) Narrow Range.
Crystals 11 00859 g003aCrystals 11 00859 g003b
Figure 4. Density of samples with the amount of antimony.
Figure 4. Density of samples with the amount of antimony.
Crystals 11 00859 g004
Figure 5. Electromechanical coupling factor (kp) of samples with the amount of antimony.
Figure 5. Electromechanical coupling factor (kp) of samples with the amount of antimony.
Crystals 11 00859 g005
Figure 6. Mechanical quality factor (Qm) of samples with the amount of antimony.
Figure 6. Mechanical quality factor (Qm) of samples with the amount of antimony.
Crystals 11 00859 g006
Figure 7. Dielectric constant (εr) of samples with the amount of antimony.
Figure 7. Dielectric constant (εr) of samples with the amount of antimony.
Crystals 11 00859 g007
Figure 8. Piezoelectric constant (d33) of samples with the amount of antimony.
Figure 8. Piezoelectric constant (d33) of samples with the amount of antimony.
Crystals 11 00859 g008
Figure 9. Piezoelectric constant (d33) of x = 0.07 samples with electric field.
Figure 9. Piezoelectric constant (d33) of x = 0.07 samples with electric field.
Crystals 11 00859 g009
Figure 10. Temperature dependence of dielectric constant with the amount of antimony.
Figure 10. Temperature dependence of dielectric constant with the amount of antimony.
Crystals 11 00859 g010
Table 1. Electrical properties of samples with the amount of antimony.
Table 1. Electrical properties of samples with the amount of antimony.
Sinter. Temp. (°C)XDensity (g/cm3)kpDielectric Constantd33(pC/N)QmTc (°C)
10600.044.3090.236152013380280
0.054.4250.412186327272250
0.064.4810.425211929359225
0.074.4880.427252133061195
0.084.4530.395288931559170
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Yoo, J.; Kang, S. Crystal Structure and Electrical Characteristics of (0.965)(Li0.03(Na0.5K0.5)0.97)(Nb1−xSbx)O3−0.035(Bi0.5Na0.5)0.9(Sr)0.1ZrO3 Ceramics Doped with CuO, B2O3, and ZnO. Crystals 2021, 11, 859. https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11080859

AMA Style

Yoo J, Kang S. Crystal Structure and Electrical Characteristics of (0.965)(Li0.03(Na0.5K0.5)0.97)(Nb1−xSbx)O3−0.035(Bi0.5Na0.5)0.9(Sr)0.1ZrO3 Ceramics Doped with CuO, B2O3, and ZnO. Crystals. 2021; 11(8):859. https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11080859

Chicago/Turabian Style

Yoo, Juhyun, and Sujin Kang. 2021. "Crystal Structure and Electrical Characteristics of (0.965)(Li0.03(Na0.5K0.5)0.97)(Nb1−xSbx)O3−0.035(Bi0.5Na0.5)0.9(Sr)0.1ZrO3 Ceramics Doped with CuO, B2O3, and ZnO" Crystals 11, no. 8: 859. https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11080859

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop