Papers by Keyword: Alkali Niobate

Abstract: K2CO3-doped 0.98(Na0.5K0.5)NbO3-0.02(Na0.5Bi0.5)TiO3 [abbreviated as 0.98NKN-0.02NBT] lead-free piezoelectric ceramics were prepared by the conventional mixed oxide process. The effects of K2CO3 additions on the crystalline structures and electrical properties of the 0.98NKN-0.02NBT ceramics were investigated. The specimens of 0.98NKN-0.02NBT ceramics added with K2CO3 maintain an orthorhombic phase. In the case of low K2CO3 content (≤ 0.3 wt%), the grain growth became remarkable. The increase of grain size favors improving the piezoelectric properties, which is known as grain size effect. The grain size effect compensates the decrease of the electromechanical coupling factor due to the hard doping effect. For 0.98NKN-0.02NBT ceramics by doping 0.3 wt% Na2CO3, the electromechanical coupling coefficients of the thickness mode kt and the planar mode kp reach 0.51 and 0.33, respectively, after sintering at 1100 oC for 3 h. Our results show that 0.98NKN-0.02NBT with the addition of 0.3 wt% K2CO3 is a good lead-free piezoelectric ceramic.

Abstract: Na_0.5K_0.5NbO₃ (NKN) lead-free piezoelectric ceramics was synthesized by a mixed oxide reaction method. The ceramics was poled under an electric field of 3 kV/mm at 150 °C for 0.5 h. The thermally stimulated depolarization current (TSDC) measurement was carried out at the heating rate of 1 °C/min from room temperature up to 500 °C under an applied voltage of 0 and 0.5 V. The zero-bias TSDC pattern showed broad patterns around at 365 and 375 °C. These temperatures corresponded to the temperatures showing bending points in the Arrhenius plot of TSDC measured under 0.5 V. The oxygen vacancy related electrical conduction was changed at 313 °C at the heating step. The mobile oxygen vacancy in NKN ceramics was piled up under the poling field, and the oxygen vacancy was diffused at temperature higher than 313 °C.

Abstract: Structural characterization of various (Li,Na,K)NbO3 solid solutions with different Li contents has been carried out by temperature-variable Raman scattering measurement. It was found that there was no clear thermal hysteresis between orthorhombic-tetragonal phase transition in the heating/cooling processes for (Li,Na,K)NbO3 ceramics with Li content of 6 wt% and above, although a noticeable thermal hysteresis is observed in the Raman spectra and dielectric constant measurement for the other specimens with lower Li contents. It is presumed that the structural change of (Li,Na,K)NbO3 cell tends to become insensibility against temperature as the Li content increases above 6.0 mol%.

Abstract: Mn-doped Na0.5K0.5NbO3 (NKN) crystals have been grown by self-flux method under several heat-treatment conditions. The cooling rate affected the quality of Mn-doped NKN crystals significantly. When the cooling rate was 0.5 oC/min at temperatures ranging from 1050 to 950 oC, the synthesized Mn-doped NKN crystal exhibited a single nucleation growth, compared with multinucleation growth when the cooling rate was 0.25 oC/min at temperatures ranging from 1050 to 950 oC. The frequency dependence on the ferroelectric P-E hysteresis loop of the Mn-doped NKN crystal was not observed at measurement frequency of 0.1 – 25 Hz. The annealed 0.5 mol% Mn-doped NKN crystal exhibited excellent P-E hysteresis loop with Pr of 45.0 μC/cm2 and Ec of 7.2 kV/cm.