Lead-Free Ceramic-Polymer Composites for Embedded Capacitor and Piezoelectric Applications P. Kumar *

Transcription

1 Lead-Free Ceramic-Polymer Composites for Embedded Capacitor and Piezoelectric Applications P. Kumar * Department of Physics, National Institute of Technology, Rourkela, Odisha, India, Correspondence to: P. Kumar ( pvn77@rediffmail.com, pawankumar@nitrkl.ac.in) Tel./fax: Abstract: Modern composite materials constitute a significant proportion of the engineered materials market ranging from everyday products to sophisticated niche applications like: charge storage in capacitors, atomic force microscopy (AFM), medical ultrasound probes, health monitoring techniques, in civil engineering, in underwater applications such as sonars submarines, in high frequency and energy harvesting applications, etc. [1,2]. Ferroelectric ceramics, polymers and their composites form a class of functional materials, that are being increasingly utilized for their specific dielectric, ferroelectric, piezoelectric, pyroelectric, electro-optic and electro-chromic as well as superconducting properties in modern electronic devices [3-5]. Considering the increased rate of utilization of the ceramics polymer composites, the present work has been undertaken to develop ceramic polymer composites to study its dielectric & piezoelectric properties. In this work, lead free (BZT-BCT) & CCTO ceramics were prepared by conventional solid state reaction route. Using XRD technique, single perovskite phase was confirmed at a calcination temperature of 1300 o C for 4h for the (BZT-BCT) system & 1050 o C for 4h for the CCTO system. The sintering of the (BZT-BCT) ceramics was carried out at 1300, 1350 and 1400 o C for 6h each, respectively. For achieving better density, the sintering of the CCTO ceramics was carried out at 1050 and 1100 o C for 8h each, respectively. PVDF (Fluka,UK) with a molecular weight ~ 5,30,000 was used for the preparation of the 0-3 composite thick films of the {0.25(BZT-BCT)-0.75[(1-x)PVDF-xCCTO]}/(BZT-BCT)- (PVDF-CCTO) system with (x = 0.02, 0.04, 0.06, 0.08 & 0.10). (BZT-BCT)-(PVDF-CCTO) composite thick films were prepared by hot uniaxial pressing. The stoichiometric proportions of the volumetric proportions of PVDF and sintered (BZT-BCT) & CCTO powders were hot pressed at ~150ºC at an applied pressure of ~6.5 MPa for 30 mins and then cooled to room temperature (RT) under pressure.

2 Epoxy resin, Araldite-AW-106 and hardener, HV-953-IN were used for the preparation of the 0-3 composite samples of the {0.2(BZT-BCT)-0.8[(1-x)epoxy-xCCTO]}/(BZT-BCT)- (epoxy-ccto) system with (x = 0.02, 0.04, 0.06, 0.08 & 0.10). Pin samples of the (BZT- BCT)-(epoxy-CCTO) composites were prepared by cold pressing and hand lay-up techniques. Maximum value of ε r ~ 4000 and max. piezoelectric coefficient (d 33 ) ~ 281 pc/n at RT were obtained in the (BZT-BCT) 50/50 ceramics samples. The RT values of r and tan at 1 khz frequency of the CCTO ceramic samples sintered at 1100 o C are found to be ~ 11,537 and 0.21, respectively. The highest values of ε r ~91 at RT and d 33 ~19pC/N of the 0.25(BZT- BCT)-0.75[(1-x)PVDF-xCCTO] composites are obtained for x=0.08. Whereas, the 0.2(BZT- BCT)-0.8[(1-x)epoxy-xCCTO] composite with x = 0.08 exhibited highest values of the r ~61 and d 33 ~15pC/N piezoelectric coefficient. These excellent dielectric and piezoelectric properties of the studied composites suggested their potential applications in embedded capacitor and piezoelectric applications. References: [1] K. K. Chawla, Composite Materials: Science and Engineering (Third Edition, Springer, New York, 2012). [2] V. Y. Topolov and C. R. Bowen, Electromechanical Properties in Composites based on Ferroelectrics (Springer, London, 2009). [3] G. Edwards, H. L. W. Chan, A. Batten, K. H. Lam, H. S. Luo and D. A. Scott, Sensors and Actuators A. 132, (2006) 434. [4] W. W. Wolny, Journal of the European Ceramic Society. 25, (2005) [5] A. J. Moulson and J. M. Herbert, Electroceramics: Materials, Properties, Applications, Second Edition (John Wiley & Sons Ltd., England, 2003).

3 Lead Free ceramic-polymer Composites for embedded capacitor and piezoelectric applications by Dr. Pawan Kumar Department of Physics N. I. T. Rourkela

4 Introduction Motivation and Objective Structural, Dielectric and Piezoelectric properties of BZT-BCT System Structural, Dielectric and Piezoelectric properties of (BZT-BCT)-PVDF and (BZT-BCT)-(PVDF-CCTO) composites Structural, Dielectric and Piezoelectric properties of (BZT-BCT)-EPOXY and (BZT-BCT)-(EPOXY-CCTO) composites Conclusions Outlines: 7/3/2015 2

5 Aim of the present work: The present work is divided into four parts: 1. To synthesize & Characterize the lead-free (BZT-BCT) ceramics near MPB. 2. To synthesize & characterize the high dielectric constant CCTO ceramics. 3. To prepare the 0-3 ceramic-polymer composites by using the ceramic powders of the best MPB composition of (BZT-BCT) system as fillers with PVDF and epoxy as the matrices. 4. To further modify the dielectric properties ( r > 50 at RT and at 1kHz frequency) of the best (BZT-BCT)/PVDF, (BZT-BCT)/epoxy composites by the addition of CCTO ceramic particles as fillers. 3

6 Part 1 To synthesize & Characterize the lead-free (BZT-BCT) ceramics near MPB and to suggest the best MPB composition 7/3/2015 Free template from 4

7 Comparison between properties of lead and lead free materials Materials ε r tanδ d 33 (pc/n) T c ( C) PZT PMN-PT NKN BNBT BZT-BCT /3/2015 5

8 Materials and method of preparation of (BZT-BCT) ceramics : x[ba(zr 0.2 Ti 0.8 )O 3 ]-(1-x)[(Ba 0.7 Ca 0.3 )TiO 3 ] (for x = 0.48, 0.50 & 0.52)/(BZT-BCT) BaCO 3, CaCO 3, ZrO 2, TiO 2 Ball milled for 8 h in acetone Sintering at 1300, 1350 & 1400 o C for 6 h TG-DSC Green pellets Calcination at 1100, 1200 & 1300 o C for 4 h 6

9 Intensity (a. u.) (001) (200) (111) (211) (002) (102) (101) Intensity (a.u.) (001) (200) (102) (111) (002) (211) Intensity (a.u.) (100) (102) (111) (220) (200) (112) (101) (101) XRD of the sintered (BZT-BCT) ceramic samples: (a) 1300 o C for 6 h 1350 o C for 6 h C for 6 h (b) 1300 o C for 6 h 1350 o C for 6 h 1400 o C for 6 h (in degrees) (in degrees) (c) * Secondary Phase 1300 o C for 6 h 1350 o C for 6 h 1400 o C for 6 h * (a) (b) (c) in degrees 7

10 Intensity (a.u.) (100) (111) (200) (102) (112) (220) (101) In te n s ity (a.u.) XRD of the (50BZT-50BCT) ceramic samples: 1300 o C for 6 h 1350 o C for 6 h 1400 o C for 6 h (d e g re e s ) (degrees) 8

11 Summary of lattice parameters of (BZT-BCT) ceramic samples: Compositions of ( BZT-BCT) system Structure Lattice parameters (Å) tetragonal a = b = c = tetragonal a = c = monoclinic a = b = c = Tetragonal a = b = c = Volume (Å 3 ) V = V = V = V =

12 tan Dielectric properties of (BZT-BCT) ceramic samples with frequency (sintered at 1400 o C): r BZT-52BCT 50BZT-50BCT 52BZT-48BCT Frequency (log 10 Hz) Frequency (log 10 Hz) 10

13 Summary of Dielectric properties of (BZT-BCT) ceramic system: Samples Dielectric parameters T c in o C r at T c r tan

14 Summary of Ferroelectric & Piezoelectric properties of (BZT-BCT) ceramic system: Compositions of (BZT-BCT) system Sintering temperature in o C P r value in µc/cm 2 E c value in kv/cm d 33 values in pc/n

15 Part II To Synthesize & Characterize the Lead-Free Dielectric Constant CCTO Ceramics 7/3/2015 Free template from 13

16 Summary of RD, Average grain size & Dielectric properties of CCTO ceramic system: Sintering temperature of CCTO ceramics in o C RD % Average grain size in µm Dielectric parameters at RT at 1 khz r tan

17 Comparison between properties of polymers Polymers ε r at 1 khz tan at 1 khz T g in C T m in C d 33 (pc/n) Poly vinylidene fluoride(pvdf) Poly vinyl chloride(pvc) Poly carbonate (PC) Epoxy polyimide 3.5(1 MHz) - >

18 Part III To prepare the (BZT-BCT)-PVDF 0-3 ceramic-polymer composites To further modify the dielectric properties of the best (BZT-BCT)/PVDF, composites by the addition of CCTO ceramic particles as fillers 7/3/2015 Free template from 16

19 Materials and method of preparation of (BZT- BCT)-PVDF composites : PVDF (Fluka) and sintered (BZT-BCT) powders. Volume % (BZT-BCT) (5 25 %). Dry magnetic stirring for 1 hour. Ultrasonification for 30 mins. Hot uniaxial pressing of the well mixed powder at 150 C and at an applied pressure of ~ 6.5 MPa for 30 min and then cooled to RT holding the pressure. Flexible, thick and self standing films were obtained. 17

20 Summary of dielectric parameters & d 33 of (BZT- BCT)-PVDF composite systems with different vol% of ceramics : Materials Vol% of ceramics r at RT at 1 khz tan at RT at 1 khz Parameters rmax at 1 khz T max at 1 khz d 33 in pc/n (BZT-BCT)-(1- ) PVDF composites = = = = =

21 Summary of dielectric parameters & d 33 of (BZT- BCT)-(PVDF-CCTO) composite systems with different vol. fractions of ceramics : Materials Vol% of ceramics r at RT at 1 khz tan at RT at 1 khz Parameters rmax at 1 khz T max at 1 khz d 33 in pc/n 0.25(BZT-BCT)- 0.75[(1-x)PVDFxCCTO] composites x = x = x = x = x =

22 Part IV To prepare the (BZT-BCT)-Epoxy 0-3 ceramic-polymer composites To further modify the dielectric properties of the best (BZT-BCT)/Epoxy, composites by the addition of CCTO ceramic particles as fillers 7/3/2015 Free template from 20

23 Materials and method of preparation of BZT-BCT. Epoxy composites : In the present work the following series of 0-3 ceramic polymer composites using epoxy as polymer matrix were prepared by cold pressing and hand lay up technique. [0.5[Ba(Zr 0.2 Ti 0.8 )O 3 ]-0.5[(Ba 0.7 Ca 0.3 )TiO 3 ]]- epoxy/ (BZT-BCT)-(1- )epoxy composites, where, = 0.05, 0.10, 0.15, 0.20 and 0.25 volume fractions. 21

24 For the preparation of the composites, sintered ceramic powders were mixed with epoxy resin and hardener (in the weight ratio of 15:1) in required volume fractions. The mixture of sintered (BZT-BCT) powder and epoxy resin was poured into the cylindrical cavity of the mould used and the two halves of the mould were fixed properly. It required proper care during the fixing of moulds, as some of the resins may squeeze out. After closing the mould properly, the specimens were allowed to solidify inside the moulds at RT for 24 h. 22

25 The steel mould was used for the preparation of cylindrical (pin) type specimen of length ~ 35 mm and diameter of ~ 10 mm. 23

26 Summary of dielectric parameters & d 33 of (BZT- BCT)-epoxy composite systems with different vol% of ceramics : Materials Vol% of ceramics r at RT at 1 khz tan at RT at 1 khz Parameters rmax at 1 khz T max at 1 khz d 33 in pc/n (BZT-BCT)-(1- ) epoxy composites = = = = =

27 Summary of dielectric parameters & d 33 of (BZT- BCT)-epoxy & (BZT-BCT)-(epoxy-CCTO) composite systems with different vol. fractions of ceramics : Materials Vol% of ceramics r at RT at 1 khz tan at RT at 1 khz Parameters rmax at 1 khz T max at 1 khz d 33 in pc/n 0.2(BZT-BCT)- 0.8[(1-x)epoxyxCCTO] composites x = x = x = x = x =

28 Major Conclusions Drawn From the Present Work: 0.50BZT-0.50BCT system sintered at 1400 o C showed better structural, microstructural, dielectric, ferroelectric and piezoelectric properties. 0.25(BZT-BCT)-0.75(PVDF) and 0.20(BZT-BCT)- 0.80(epoxy) ceramic-polymer composites are suitable for capacitor & energy harvesting applications. Dielectric and piezoelectric properties of [0.25(BZT- BCT)-0.69(PVDF)-0.06(CCTO)] and [0.20(BZT-BCT) (Epoxy)-0.064(CCTO)] ceramic-polymer composites are better than the existing reports and suggested their suitability for flexible capacitor devices and for energy harvesting piezoelectric applications.

29 27