Luong Huu Bac

Current Development in Lead-Free -Based Piezoelectric Materials

The lead-free piezoelectric ceramics display good piezoelectric properties which are comparable with Pb(Zr,Ti)O3 (PZT) and these materials overcome the hazard to the environment and human health. The Bi0.5(Na,K)0.5TiO3 (BNKT) is rapidly developed because of good piezoelectric, ferroelectric, and dielectric properties compared to PZT. The origin of giant strain of BNKT piezoelectric materials was found at morphotropic phase boundary due to crystal change from tetragonal to orthorhombic and/or precipitation of cubic phases, in addition to domain switching mechanism. The dopants or secondary phases with ABO3 structure as solid solution are expected to change the crystal structure and create the vacancies which results in enhancement of the piezoelectric properties. In this work, we reviewed the current development of BNKT by dopants and secondary phase as solid solution. Our discussion will focus on role of dopants and secondary phase to piezoelectric properties of BNKT. This result will open the direction to control the properties of lead-free piezoelectric materials.

Role of Sintering Temperature on Giant Field-Induced Strain in Lead-Free Bi0.5(Na,K)0.5TiO3-Based Ceramics

The effect of sintering temperature on the giant electric field-induced strain was observed in lead-free Bi0.5(Na0.77 Li0.05K0.18)0.5(Ti0.975Ta0.025)O3 ceramics. The grains size and dense structure increased with increasing of the sintering temperature. The growth of polar phases was observed in non-polar phase when sintering temperature increased. The giant electric field-induced strain strongly enhanced up to Smax/Emax = 800 pm/V, resulting from coexistence of polar and non-polar phases. The highest values of Smax/Emax were higher than those were previously reported on non-textured lead-free piezoelectric ceramics.

Theoretical and experimental studies on the influence of Cr incorporation on the structural, optical, and magnetic properties of Bi0.5K0.5TiO3 materials

AbstractMultiferroic materials based on lead-free ferroelectric materials have potential applications in the fabrication of next-generation devices. Herein, the sol–gel method is used to synthesize pristine and Cr-doped Bi0.5K0.5TiO3 nanocrystals. Density functional theory simulation is performed to elucidate the mechanism underlying the observed electronic and magnetic properties of the nanocrystals. In materials doped with 9 mol% Cr, the substitution of Cr in the Ti site decreases the optical band gap from 3.09 eV to 2.26 eV and induces ferromagnetism at room temperature. The saturation magnetization of the materials is approximately 0.18 μB/Cr at 5 K and can be attributed to the interplay of the unpaired electron counts of Cr3+ ions in the crystal field mechanism and Jahn–Teller effect. Pristine Bi0.5K0.5TiO3 samples exhibit weak ferromagnetism at room temperature, given the existence of the mixed valence states of Ti4+ and Ti3+ and the formation of O or Ti vacancies during sample growth. The present study provides deep insight into the induction of magnetism in ferroelectric materials doped with transition metals. Such materials have potential spintronic applications. HighlightsThe Cr-doped Bi0.5K0.5TiO3 materials were fabricated by the sol–gel method.The room-temperature ferromagnetism in Cr-doped samples was obtained.Optical band gap was reduced from 3.09 eV to 2.26 eV.Defect-induced room-temperature ferromagnetism was investigated by density functional theory calculations.