Lead-Free Ceramic-Polymer Composites for Embedded Capacitor and Piezoelectric Applications

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 1300oC for 4h for the (BZT-BCT) system & 1050oC for 4h for the CCTO system. The sintering of the (BZT-BCT) ceramics was carried out at 1300, 1350 and 1400oC for 6h each, respectively. For achieving better density, the sintering of the CCTO ceramics was carried out at 1050 and 1100oC 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. 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 (BZTBCT)-( epoxy-CCTO) composites were prepared by cold pressing and hand lay-up techniques. Maximum value of εr~ 4000 and max. piezoelectric coefficient (d33) ~ 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 1100oC are found to be ~ 11,537 and 0.21, respectively. The highest values of εr ~91 at RT and d33 ~19pC/N of the 0.25(BZTBCT)- 0.75[(1-x)PVDF-xCCTO] composites are obtained for x=0.08. Whereas, the 0.2(BZTBCT)- 0.8[(1-x)epoxy-xCCTO] composite with x = 0.08 exhibited highest values of the r ~61 and d33 ~15pC/N piezoelectric coefficient. These excellent dielectric and piezoelectric properties of the studied composites suggested their potential applications in embedded capacitor and piezoelectric applications.