ME response of cofired trilayer magnetoelectric composites with partial texturing

Magnetoelectric (ME) effect is the combination of two types of materials property such as magnetostriction and piezoelectricity [1–3]. ME effect can be described as the induced electrical polarization under magnetic field or induced magnetization under electric field. The interrelation between ferroelectricity and magnetism allows the magnetic control of ferroelectric properties and vice versa [4–7]. The composite systems are easy to fabricate as compared to the single phase materials, cost effective, and have higher working temperature range [8–10]. Sintered composites fabricated by mixing of piezoelectric and ferromagnetic phases have been widely studied because of its simplicity in synthesis using well-established conventional ceramic processing technique. To enhance the ME coefficient of sintered composite, it is necessary to optimize the composition, microstructural features (grain size, grain orientation), geometry, and sintering parameters. In our previous studies, it have been shown that soft piezoelectric phase (high dielectric and piezoelectric constant), soft magnetic phase (high permeability and low coercivity) [11], large piezoelectric grain size ([1 lm) [12], layered structure (bilayer/trilayer) [13], and post-sintering thermal treatment (annealing and aging) [14] improve the ME property. For synthesizing the cofired trilayer composite, we introduced the noble pressure assisted sintering. We use this process to investigate the effect of grain texturing on ME coefficient of the trilayer composite. Crystallographic texturing of piezoelectric phase can improve the piezoelectric and ferroelectric response by exploiting the anisotropy of electrical properties. Results have been reported in literature on the effect of texturing in both lead-based and lead-free materials including BTO, PMN-PT, NBT-BT, and KNN [15–18]. The goal of this study was to implement the known texturing process in heterogeneous system consisting of varying crystal structure. This will allow developing novel hybrid materials that exhibit maximum response. As a simple rule, the rhombohedral phase oriented along the h100i direction provides higher piezoelectric response. Texturing can be accomplished through various processes including, hot pressing (HP), templated grain growth (TGG) [19], and reactive template grain growth (RTGG) [15]. The advantage of TGG over HP is that the process is conducted using steps similar to that of conventional ceramic processing except with added seed material. In HP there is a chance of abnormal grain growth. Hence in this study, the TGG technique was adopted to synthesize the textured ME coefficient. The texturing process consists of two important steps (i) seed fabrication and (ii) seed alignment in the matrix [20]. To fabricate the seed (template), molten salt synthesis technique was utilized. In this respect, BaTiO3 was chosen as the seed material since it can be grown in large size using Remeika process [21]. This synthesis process consists of heating the raw materials (BTO covered with KF salt in Pt crucible) in the temperature range of 1150– 1225 C (±5 C) for 8–12 h and then slowly cooling down to the room temperature. The crystals were separated from R. A. Islam (&) Materials Science and Engineering, University of Texas at Arlington, Arlington, TX 76019, USA e-mail: rashed_ms@yahoo.com