**Piezoelectric Properties and Microstructure of (K,Na)NbO3–KTiNbO5 Composite Lead-Free Piezoelectric Ceramic**

Kazushige Ohbayashi

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http://dx.doi.org/10.5772/62869

#### **Abstract**

We developed a (K,Na)NbO3-based lead-free piezoelectric ceramic with a KTiNbO5 system, (K1−*<sup>x</sup>*Na*x*)0.86Ca0.04Li0.02Nb0.85O3−δ–KTiNbO5–BaZrO3–Co3O4–Fe2O3–ZnO (KNN– NTK composite). This KNN–NTK composite exhibits a very dense microstructure, and *k*p = 0.52, *ε*33T/*ε*0 = 1600, and *d*33 = 252 pC/N. We found that a portion of the KTiNbO5 converted into K2(Ti,Nb,Co,Zn)6O13 and/or CoZnTiO4. We were able to reproducibly prepare granulated powder of KNN–NTK in batches of 100 kg using a spray-dryer. In addition, we performed a detailed investigation of the microstruc‐ ture of KNN–NTK composite. The results show that a tetragonal and an orthorhom‐ bic phase coexist in a main KNN phase over a wide range of 0.56 ≤ *x* ≤ 0.75. The granular nanodomains of the orthorhombic phase dispersed within the tetragonal matrix in the KNN phase. A maximum value of *k*p = 0.56 occurred for *x* = 0.56. The Na fraction *x* corresponding to maximum *k*p was also the minimum *x* required to generate the orthorhombic phase. We conclude that the KNN–NTK composite exhibits excellent piezoelectric properties because of the two-phase coexisting state. This gentle phase transition of KNN–NTK composite seems to be a relaxor, but the diffuseness degree *γ* = 1.07 suggests otherwise.

**Keywords:** (K,Na)NbO3, lead-free, microstructure, two-phase coexisting, coupling co‐ efficient

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