AUTHOR=Khesro Amir , Wang Dawei , Hussain Fayaz , Muhammad Raz , Wang Ge , Feteira Antonio , Reaney Ian M. 

TITLE=Temperature Dependent Piezoelectric Properties of Lead-Free (1-x)K0.6Na0.4NbO3–xBiFeO3 Ceramics

JOURNAL=Frontiers in Materials

VOLUME=7

YEAR=2020

URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2020.00140

DOI=10.3389/fmats.2020.00140

ISSN=2296-8016

ABSTRACT=<p>(1-<italic>x</italic>)K<sub>0.4</sub>Na<sub>0.6</sub>NbO<sub>3</sub>–<italic>x</italic>BiFeO<sub>3</sub> lead-free piezoelectric ceramics were successfully prepared in a single perovskite phase using the conventional solid-state synthesis. Relative permittivity (ε<sub>r</sub>) as a function of temperature indicated that small additions of BiFeO<sub>3</sub> not only broadened and lowered the cubic to tetragonal phase transition (<italic>T</italic><sub>C</sub>) but also shifted the tetragonal to orthorhombic phase transition (<italic>T</italic><sub>O–T</sub>) toward room temperature (RT). Ceramics with <italic>x</italic> = 1 mol.% showed optimum properties with small and large signal piezoelectric coefficient, <italic>d</italic><sub>33</sub> = 182 pC/N and <italic>d</italic><sup>∗</sup><sub>33</sub> = 250 pm/V, respectively, electromechanical coupling coefficient, <italic>k</italic><sub><italic>p</italic></sub> = 50%, and <italic>T</italic><sub>C</sub> = 355°C. <italic>k</italic><sub><italic>p</italic></sub> varied by ∼5% from RT to 90°C, while <italic>d</italic><sup>∗</sup><sub>33</sub> showed a variation of ∼15% from RT to 75°C, indicating that piezoelectric properties were stable with temperature in the orthorhombic phase field. However, above the onset of <italic>T</italic><sub>O–T</sub>, the properties monotonically degraded in the tetragonal phase field as <italic>T</italic><sub>C</sub> was approached.</p>