Temperature dependent properties and poling effect of K4CuNb8O23 modified (Na0.5K0.5)NbO3 lead free piezoceramics

Lead free piezoelectric ceramics (Na0.5K0.5)NbO3 modified by 4% mol. K4CuNb8O23 (abbreviated NKN:4KCN hereinafter) contain moderate piezoelectric constant d(33) similar to 100 pC N-1 and large mechanical quality factor Q(m)>1000, showing possible replacement of the lead-based ones (Chen et al., J Appl. Phys. 102, 104109 (2007)). In terms of practical use, however, the temperature stability of NKN:4KCN is not clear to date. We made a systematic investigation on the properties versus temperature of NKN:4KCN to evaluate whether it can be practically used. In the range from room temperature (RT similar to 25 degrees C) to 100 degrees C, the ferroelectricity of poled NKN:4KCN material is nearly temperature independent, remanent polarization P-r is about 27.6 +/- 1 mu C cm(-2). When the as-studied NKN:4KCN ceramics were thermal depolarized in temperature range from RT to 450 degrees C, piezoelectric constant d(33) changed little, retaining about 99 pC N-1, 77 +/- 3 pC N-1, from RT to 150 degrees C, 200 degrees C to 350 degrees C, respectively. The poled NKN:4KCN material showed higher orthorhombic to tetragonal phase transition temperature (TO-T similar to 200 degrees C) compared to unpoled sample (TO-T similar to 194 degrees C). Moreover, this kind of lead free material displayed negative temperature coefficient of frequency (TCF) and positive TCF in orthorhombic and tetragonal phase state, respectively. The TCF was about -360 ppm K-1 in the range from RT to 125 degrees C, close to some lead-based commercial ones. The significance of this work lies in evaluating whether such a material can be practically used or not. We believe such a material might be the most promising candidate for replacing lead-based ones in some areas in the future. (C) 2015 AIP Publishing LLC.