Effects of Non‐Stoichiometry on the Microstructure, Oxygen Vacancies, and Piezoelectric Properties of CuTa 2 O 6 ‐Doped NKN Ceramics

The effects of non‐stoichiometry on the microstructure, oxygen vacancies, and piezoelectric properties of ( Na 0.5 K 0.5 ) x NbO 3 ( NK x N , where x  =   0.98, 1.00, 1.01, and 1.02) ceramics doped with sintering aid CuTa 2 O 6 ( CT ) doping were investigated. X‐ray diffraction (XRD) patterns indicated that a secondary phase formed in CT‐doped NK x N ( NK x NCT ) ceramics with x  <   1.00 and that a pure phase was obtained with x  ≥   1.00. The grain size of NK x NCT ceramics increased with increasing x value due to the formation of a liquid phase. The internal bias field, activation energy, and Raman analysis for NK x NCT ceramics showed that the number of induced oxygen vacancies increased with decreasing x value. The high mechanical quality factor ( Q m ) value obtained for NK x NCT ceramics did not correspond to a higher concentration of oxygen vacancies, illustrating that the suitable compensation (excess Na and K ) is more important than the concentration of oxygen vacancies to obtain the ceramics with high Q m values. The NK x NCT ceramics with x  =   1.01 exhibited excellent piezoelectric properties, with k p and Q m values of 39.9% and 2,070, respectively.