Composition-Driven Phase Boundary and Piezoelectricity in Potassium–Sodium Niobate-Based Ceramics

The piezoelectricity of (K,Na)­NbO₃ ceramics strongly depends on the phase boundary types as well as the doped compositions. Here, we systematically studied the relationships between the compositions and phase boundary types in (K,Na) (Nb,Sb)­O₃–Bi_0.5Na_0.5AO₃ (KNNS-BNA, A = Hf, Zr, Ti, Sn) ceramics; then their piezoelectricity can be readily modified. Their phase boundary types are determined by the doped elements. A rhombohedral-tetragonal (R–T) phase boundary can be driven in the compositions range of 0.035 ≤ BNH ≤ 0.040 and 0.035 ≤ BNZ ≤ 0.045; an orthorhombic-tetragonal (O–T) phase boundary is formed in the composition range of 0.005 ≤ BNT ≤ 0.02; and a pure O phase can be only observed regardless of BNS content (≤0.01). In addition, the phase boundary types strongly affect their corresponding piezoelectricities. A larger <i>d</i>₃₃ (∼440–450 pC/N) and a higher <i>d</i>₃₃* (∼742–834 pm/V) can be attained in KNNS-BNA (A = Zr and Hf) ceramics due to the involvement of R–T phase boundary, and unfortunately KNNS-BNA (A = Sn and Ti) ceramics possess a relatively poor piezoelectricity (<i>d</i>₃₃ ≤ 200 and <i>d</i>₃₃* < 600 pm/V) due to the involvement of other phase structures (O–T or O). In addition, the underlying physical mechanisms for the relationships between piezoelectricity and phase boundary types were also discussed. We believe that comprehensive research can design more excellent ceramic systems concerning potassium–sodium niobate

New Potassium–Sodium Niobate Ceramics with a Giant <i>d</i>₃₃

For potassium–sodium niobate, poor piezoelectric properties always perplex most researchers, and then it becomes important to attain a giant piezoelectricity. Here we reported a giant piezoelectric constant in (1 – <i>x</i>)­(K_0.48Na_0.52)­(Nb_0.95Sb_0.05)­O₃-<i>x</i>Bi_0.5Ag_0.5ZrO₃ lead-free ceramics. The rhombohedral-tetragonal phase boundary was shown in the ceramics with 0.04 < <i>x</i> ≤ 0.05, and then the ceramic with <i>x</i> = 0.0425 possesses a giant <i>d</i>₃₃ of ∼490 pC/N. We also discussed the physical mechanisms of enhanced piezoelectricity. As a result, such a research can benefit the sustainable development of (K,Na)­NbO₃ materials