High-sensitivity piezoelectric perovskites for magnetoelectric composites

Abstract

A highly topical set of perovskite oxides are high-sensitivity piezoelectric ones, among which Pb(Zr,Ti)O3 at the morphotropic phase boundary (MPB) between ferroelectric rhombohedral and tetragonal polymorphic phases is reckoned a case study. Piezoelectric ceramics are used in a wide range of mature, electromechanical transduction technologies like piezoelectric sensors, actuators and ultrasound generation, to name only a few examples, and more recently for demonstrating novel applications like magnetoelectric composites. In this case, piezoelectric perovskites are combined with magnetostrictive materials to provide magnetoelectricity as a product property of the piezoelectricity and piezomagnetism of the component phases. Interfaces play a key issue, for they control the mechanical coupling between the piezoresponsive phases. We present here main results of our investigation on the suitability of the high sensitivity MPB piezoelectric perovskite BiScO3–PbTiO3 in combination with ferrimagnetic spinel oxides for magnetoelectric composites. Emphasis has been put on the processing at low temperature to control reactions and interdiffusion between the two oxides. The role of the grain size effects is extensively addressed.

Insights into the Performance of Magnetoelectric Ceramic Layered Composites

“…Therefore, q (H) was evaluated from these experimental curves, and a Q 111 value of 1 × 10 −8 g 2 ·emu −2 that was calculated from the saturation strain and magnetization of coarse-grained ceramics:~25 × 10 −6 [14] and~50 emu·g −1 [21]. There is a good agreement between the latter value and the saturation magnetization for the NiFe 2 O 4 -Bi 0.36 Pb 0.64 Sc 0.36 Ti 0.64 O 3 composite processed by SPS at 1000 • C [18]. The rest of the parameters were directly taken from [12,22,23].…”

“…However, magnetization curves are known to be very sensitive to microstructure with a direct effect on the effective piezomagnetic coefficients. Experimental magnetization curves for the actual composites to be simulated can be found in [18]. Indeed, a distinctive evolution of the curves with processing temperature and thus, with microstructure was found.…”

“…This configuration is the L-T magnetoelectric mode, for which the α 31 E transverse field coefficient is readily derived as the ratio between the voltage difference and magnetic field amplitudes, normalized to the total thickness of the structure, for varying magnetizing fields. Unless specified, an alternate magnetic field of 10 Oe amplitude and 10 kHz frequency was used, while the magnetizing field was changed in steps between 1 and −1 kOe, which were the measuring conditions in [18]. Unclamped (stress-free) and open-circuit (zero current) mechanical and electrical boundary conditions were selected, respectively, while continuity of in-plane strain, of normal electrical displacement, and of normal magnetic field was imposed across the magnetostrictive-piezoelectric interfaces to couple the two components.…”

“…Input material coefficients for the simulations are given in Table 1 for the magnetostrictive ceramic material and in Tables 2 and 3 for the piezoelectric one. Actual composites, whose magnetoelectric response is being compared with simulations are high-quality NiFe 2 O 4 -Bi 0.36 Pb 0.64 Sc 0.36 Ti 0.64 O 3 ones with crack-free, fully-functional interfaces that have been processed by spark plasma sintering (SPS) of nanocrystalline powders at temperatures between 1000 • C and 800 • C to minimize chemical reactions at, and interdiffusion across, the interface [18]. The selected advanced processing has a distinctive effect on the microstructure of the two ceramic components, and material coefficients for coarse-grained materials cannot blissfully be used for the simulations.…”

“…We report here a FEA simulation of the magnetoelectric response of three-layer and multilayer composite discs with finite diameter to thickness ratio, also considering the actual conductivity of the magnetic component. The NiFe 2 O 4 -Bi 0.36 Pb 0.64 Sc 0.36 Ti 0.64 O 3 system was chosen as a case study because experimental magnetoelectric coefficients are readily available for ceramic co-fired high-quality laminate composites [18].…”