Revealing the influence of Nb-doping on the crystal structure and electromechanical properties of (K, Bi)(Mg, Ti, Nb)O3 ceramics

초록

Nb-modified lead-free ceramics (K0.48Bi0.52)(Mg0.02Ti0.98-xNbx)O-3, (KBT-BMTNbx with x = 0.00 - 0.05) were synthesized by a conventional solid-state reaction route followed by furnace cooling. The effects of Nb-doping on the structural properties and electrical properties of KBT-BMTNbx ceramics have been investigated. The X-ray diffraction pattern indicates a mixed tetragonal and cubic phase for the pure KBT-BMTNbx ceramics. Therefore, a large piezoelectric actuator coefficient d(33)* & AP; 700 pm/V, piezoelectric sensor coefficient (d(33) & AP; 133 pC/N) along with remnant polarization (P-r & AP; 17.5 & mu;C/cm(2)), maximum electromechanical strain & AP; 0.35% and maximum temperature (T-m & AP; 336 oC) were obtained for KBT-BMTNbx. However, with Nb-doping, a compositionally driven phase transformation occurred from mixed rhombohedral and tetragonal phases to cubic phase. Because of the excess Nb-doping in the KBT-BMT ceramics, the grain size suddenly decreased, as a result, the long-range ferroelectric phase was converted into a short-range relaxor phase. Hence, a low dielectric loss tan & delta; & AP; 0.02 was achieved at x = 0.02 composition. This superior dielectric performance is correlated to the crystal structure morphotropic phase boundary, optimum grain size (& AP; 2 & mu;m), maximum lattice distortion, and soft-ferroelectric effect induced by the donor doping. The main aim of recent research is to investigate P-r, d(33), d(33)*, S-max,S- and reduced tan & delta; for practical applications in the real world.

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