Synthesis and characterisation of lead free BaFe12O19 -(K0.5Na0.5)NbO3 magnetoelectric composites, and the comparison of various synthetic routes

[摘要] Polycrystalline lead-free (1-x)BaFe12O19-x(K0.5Na0.5)NbO3 magnetoelectric ceramic composites (x = 10, 20 and 30 wt%) were fabricated for the first time, comparing various synthesis techniques, namely solid state reaction, sol-gel, co-precipitation and citrate combustion methods for the synthesis of the ferrite phase. As well as the four synthesis routes, comparisons were made between uniaxial pressing and cold isostatic pressing of the samples prior to sintering at 1200 degrees C/2 h. Formation of separate magnetic hexaferrite BaFe12O19 (BaM) and ferroelectric (K0.5Na0.5)NbO3 (KNN) phases in the composites was confirmed using x-ray diffraction. The microstructural features revealed distribution of BaM and KNN grains in all the composite systems. Piezoresponse (PFM) and magnetic force (MFM) modes of scanning probe microscopy (SPM) were utilised to assess responses from piezoelectric and magnetic grains. Localised piezoelectric hysteresis loops were measured on KNN grains in composites made by all four methods. Typical hard magnetic hysteresis loops for BaM were observed exhibiting high coercivity values (up to 281 kA m(-1) or 3530 Oe), and those composites made using solid state reaction and citrate combustion methods, which contained no impurity phases, had close to maximum magnetisation values (equivalent to similar to 70 A m(2) kg(-1) for the BaM phase). SEM, MFM and magnetisation measurements all suggested that the grain size of the BaM in the composites made using solid state reaction, co-precipitation and citrate combustion methods was around 1 mu m, and consisting of single magnetic domains. As a result, it is likely that these samples will exhibit a high degree of magnetoelectric coupling. (C) 2021 Elsevier B.V. All rights reserved.

[发布日期] 2021-11-25

[关键词] M-type hexaferrites;KNN;Lead-free composites;PFM;MFM