Investigating the importance of strain-coupling in lead-free 2–2 relaxor/ferroelectric composites with digital image correlation

Abstract

Ceramic-ceramic composite structures are a viable solution to improve the electromechanical response of lead-free ferroelectrics through tuning of the local electrical and mechanical fields. The origin of the enhanced properties, however, remains unclear, as many of the possible effects, such as polarization and strain coupling as well as interface diffusion, are interrelated and difficult to separate or directly investigate. In this study, we use a custom-built digital image correlation system to directly investigate the influence of strain coupling on 2-2 composites consisting of 0.90Na1/2Bi1/2TiO3-0.06BaTiO3-0.04K0.5Na0.5NbO3 (NBT-6BT-4KNN) and 0.94Na1/2Bi1/2TiO3-0.06BaTiO3 (NBT-6BT) by varying the mechanical interface contacts between end members. Specifically, two model cases were utilized to separate the relative contributions of the polarization and strain coupling mechanisms: (i) electrically connected and (ii) mechanically and electrically connected. The local strain gradient was characterized through the thickness of the composite across different layers as well as the interface, where the macroscopic large signal longitudinal and transverse ferroelectric response was determined. Experimental results reveal an enhancement of the large signal piezoelectric coefficient d_33^* by approximately 10 % from 390 pm/V to 440 pm/V due to strain coupling.

Novel lead-free 2–1–2 composite: predicted high piezoelectric sensitivity and significant hydrostatic response

“…Matrix of effective electromechanical properties of the 2-1-2 composite ||C (1) || Matrix of electromechanical properties of layers of the first type in the 2-1-2 composite ||C (2) || Matrix of electromechanical properties of layers of the second type in the Tensor of electroelastic moduli of the layer K Axis of the main coordinate system connected with the 2-1-2 composite sample OX ′ j Axis of the coordinate system connected with the single crystal rod in the layer of the second type P…”

“…In equation ( 4), m is the volume fraction of the main SC component (i.e. the volume fraction of the LFT) in the composite sample, C (1) and C (2) describe the electromechanical properties of the LFT and LST, respectively, ∥M∥ is the matrix associated with boundary conditions [2,27] for electric and mechanical fields at the LFT/LST interface x 1 = const (figure 1) and ∥I∥ is the identity matrix. Every matrix from equation ( 4) is a 9 × 9 matrix.…”

“…Every matrix from equation ( 4) is a 9 × 9 matrix. The C (1) and C (2) matrices from equation ( 4) are given by…”

“…Progress and innovation in the field of piezo-active composites based on smart materials are inextricably linked in the search for effective components and their combinations in new composite structures [1][2][3]. Different combinations of components make it possible to achieve large effective physical properties and parameters in specific volume-fraction ranges by considering composite microgeometry, domain structure, symmetry of components [2][3][4][5], polarisation orientation effects and other factors [6][7][8][9].…”

Influence of Oxygen Vacancies on the Impedance Spectrum of Al2O3–Na0.5K0.5NbO3 Composites

“…Furthermore, among piezoelectric properties, the piezoelectric charge coefficient d 33 can reach values between 350 and 650 pC/N, similar to common lead zirconate titanate (PZT) compositions [1,2]. To further increase important values for sensor [3,4] or actuator applications [4,5], composites are a viable option. Therefore, the concept of ceramic/ceramic composites for energy-harvesting applications was explored using the model material NKN + 0.2% MnO/Al 2 O 3 in a recent study [6].…”