Review of chemical modification on potassium sodium niobate lead-free piezoelectrics

Abstract

Heterogeneity at different length scales.

Reduced degree of phase coexistence in KNN-Based ceramics by competing additives

“…The unipolar strain (Suni) monotonically decreases with an increasing x (Figure 7(d)), suggesting the decreasing converse piezoelectric response and non-180o domain switching [38]. 13 Figures 8(c, d). With an increasing x, Ec and Pr monotonically reduce, indicating the decreased ferroelectricity.…”

“…where XA and XB are the electronegativity values of two different elements [13]. The ion radius, electronegativity, and bonding fraction with the oxygen of A-site ions are listed in Table 2.…”

“…Although the phase boundary can be empirically obtained by trying different additives or summarizing additives from the reported investigations [13], it is still needed to further understand how additives influence the phase structure from other aspects, such as ionic radii, electronegativity, hybridization, and polarizability [13]. Thus, the current consideration or choice for additives still remains in the exploratory stage, which hinders the further development of KNN-based ceramics.…”

“…Thus, the current consideration or choice for additives still remains in the exploratory stage, which hinders the further development of KNN-based ceramics. When surveying the reported additives, ion substitutions (e.g., Li+, Ag+, Sb5+, and Ta5+) and/or ABO3-type additives were found to effectively construct the phase boundary and obtain high d33 values [1,2,13]. Particularly, A2+B4+O3-type additives, represented by (Bi0.5M0.5)NO3 (M=Na/Ag/K, N=Zr/Hf), were widely utilized 3 to reduce TO-T [14][15][16].…”

“…However, other additives, which have the same type but different combined ions, were reported to slightly influence TO-T when comparing with the former in the same content, such as ABO3 (A=Ca/Ba/Sr, B=Zr/Hf) [17][18][19][20]. The recent statistics reveal that additions of Sb5+ and Bi3+ are extremely crucial for achieving high d33 values [13]. Therefore, it is highly speculated that Bi3+ plays a significant role in the effect of (Bi0.5M0.5)NO3 (M=Na/Ag/K, N=Zr/Hf) on KNN-based ceramics' TO-T.…”