Fabrication and Characterizations of Piezoelectric Ceramic/Polymer Composites with 1-3 Connectivity

Abstract

Piezoceramic/polymer composites with 1-3 connectivity are the most extensively studied and utilized for different applications among existing 10 types of diphasic composites. This type of composite consists of individual piezoceramic rods or fibers aligned in the direction parallel to poling and embedded in a polymer matrix. The piezoceramic fiber or rods play an active role for energy conversion between the mechanical and electrical energy, while the polymer phase acts as a passive medium and transfers the mechanical energy between the piezoelectric ceramic and surrounding with which the composite interacts. These composites are widely used in underwater hydrophone applications, ultrasound actuators and sensors in medical diagnostic devices. In this study, piezoceramics modified compositions; Pb/Co doped barium titanate (Ba0.95Pb0.05)(Ti0.99Co0.01)O3 (BT-PC) and Sr doped lead zirconate titanate (Pb0.94Sr0.04)(Zr0.52Ti0.48)O3 (PZT-S) were synthesized through solid state reaction method. Self-synthesized BT-PC powder has particle size ~0.4μm and after sintering and poling its key properties were; εr= 1100, d33= 136pC/N, g33= 14×10-3 Vm/N, kt=31%, and tanδ= 0.005. Likewise, the basic properties of the PZT-S were; εr= 1327, d33= 335pC/N, g33= 29×10-3 Vm/N, kt=45%, and tanδ= 0.030. Beside these, a novel Pbfree potassium sodium niobate (KNN) based optimized composition 0.9475(Li0.02(Na0.53K0.48)0.98)(Nb0.80Ta0.20)O5-0.0525AgSbO3-0.5wt.%MnO2, (LKNNT -AS-M) with electrical properties; εr= 1927, d33= 287pC/N, g33= 17×10-3 Vm/N, kt=38%, and tanδ= 0.038 was also used as an active phase. Monothane-A70, araldite- F, and Epo-Tek 301 were used as a passive polymer matrix in this work. Three different techniques named as; a novel die-pressing technique, modified align-and-fill, and improved dice-and-fill technique were used for the fabrication of 1-3 composites. Several series of the composites including; BT-PC/monothane-A70, PZT-S/monothane-A70, PZT-S/araldite-F, and LKNNT-AS-M/Epo-Tek 301 with varying piezoceramics rods diameter, spacing between the rods and aspect ratio were developed. The composites developed through die-pressing and align-and-fill techniques possess piezoceramics rods diameter ~1.20mm and ~0.78mm respectively with ceramics contents 11-35 vol. %. However, with dice-and-fill process the LKNNTxiv AS-M ceramic pillars cross-sectional dimensions were 50´50μm with relatively high aspect ratio up to 11. In addition, an underwater transducer with sample changing options was developed indigenously. Disc shape samples of monolithic piezoceramic and 1-3 composite were assembled in the self-designed transducer individually. Transducer’s underwater voltage receiving sensitivity (Sh) and transmitting voltage response (Sv) were investigated in the frequency range 10-200 kHz using a calibrated projector method with pulse technique Developed 1-3 composites were passed through comprehensive microstructural, dielectric, elastic and resonance investigations. Results revealed that all the fabricated 1-3 composites possess clear thickness resonance modes without any mode coupling. The BT-PC/monothane-A70 composites exhibited thickness coupling factor kt (~44%), figure of merit FOM (up to 7169fm2/N), acoustic impedance Z (8-13Mrayl) and elastic stiffness C33 D (36-65GPa). The PZT-S based composites exhibited superior properties due to high piezoelectric charge coefficient (d33~335 pC/N) and high electromechanical coupling coefficient (k33~67%) of PZT-S compared to BT-PC piezoceramic. In addition, low stiffness (C33 D ~ 21-55 GPa) PZT-S/monothane-A70 composites have better acoustic impedance (Z ~ 6-14 Mrayl), high charge coefficient (d33~202-271 pC/N), high hydrostatic charge and voltage coefficients (dh ~ 136-171 pC/N, gh ~ 33- 114×10-3 Vm/N) and high figure of merit (FOM ~ 4488-19364 fm2/N) compared to the PZT-S/araldite-F composites encompassing high stiffness (C33 D ~ 23-60 GPa). The Pb-free LKNNT-AS-M/Epo-Tek 301 composites also exhibited the enhanced properties such as higher thickness factor kt ~63-67%, lower planar factor kp ~27-34%, higher kt/kp ratio ~2.3, low electrical (tanδ ~0.027) and mechanical (Qm ~9) losses, encouraging acoustic impedance Z ~4.2-7.8Mrayl and ~5 times higher voltage coefficient g33 compared to LKNNT-AS-M piezoceramic. Likewise, the underwater results revealed that the transducer with 1-3 PZT-S/araldite-F sample exhibited better voltage receiving sensitivity Sh (-214dB ref 1V/μPa) due to its ~295% higher piezoelectric voltage coefficient gh (30´10-3Vm/N) compared to PZT-S. The above mentioned promising results of the developed composites indicate that they have the potential to be used as active elements in high performance ultrasonic transducers.