• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.10
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• pp.637-640
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• 2017

In this study, $(1-x)(Na_{0.52}K_{0.443}Li_{0.037})(Nb_{0.883}Sb_{0.08}Ta_{0.037})O_3-x(Bi_{0.5}(Na_{0.7}K_{0.3})_{0.5}ZrO_3$ ceramics were fabricated by BNKZ substitution using a conventional solid-state method to develop excellent lead-free piezoelectric ceramics for piezoelectric actuators; their dielectric and piezoelectric properties were then investigated. All specimens were in the orthorhombic phase. $NKL-NSTO_3$ ceramics with x=0.01 showed excellent piezoelectric properties. The density (${\rho}$), piezoelectric charge constant ($d_{33}$), planar piezoelectric coupling coefficient ($k_p$), mechanical quality factor ($Q_m$), and dielectric constant (${\varepsilon}_r$) had optimized values of $4.56g/cm^3$, 208 pC/N, 0.43, 96, and 975, respectively.

• Korean Journal of Materials Research
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• v.34 no.2
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• pp.116-124
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• 2024

In this study, we investigated the microstructure and piezoelectric properties of 0.96(K_0.456Na_0.536)Nb_0.95Sb_0.05-0.04Bi_0.5(Na_0.82K_0.18)_0.5ZrO₃ (KNNS-BNKZ) ceramics based on one-step and two-step sintering processes. One-step sintering led to significant abnormal grain (AG) growth at temperatures above 1,085 ℃. With increasing sintering temperature, piezoelectric and dielectric properties were enhanced, resulting in a high d₃₃ = 506 pC/N for one-step specimen sintered at 1,100 ℃ (one-step 1,100 ℃ specimen). However, for one-step 1,115 ℃ specimen, a slight decrease in d₃₃ was observed, emphasizing the importance of a high tetragonal (T) phase fraction for superior piezoelectric properties. Achieving a relative density above 84 % for samples sintered by the one-step sintering process was challenging. Conversely, two-step sintering significantly improved the relative density of KNNS-BNKZ ceramics up to 96 %, attributed to the control of AG nucleation in the first step and grain growth rate control in the second step. The quantity of AG nucleation was affected by the duration of the first step, determining the final microstructure. Despite having a lower T phase fraction than that of the one-step 1,100 ℃ specimen, the two-step specimen exhibited higher piezoelectric coefficients (d₃₃ = 574 pC/N and k_p = 0.5) than those of the one-step 1,100 ℃ specimen due to its higher relative density. Performance evaluation of magnetoelectric composite devices composed of one-step and two-step specimens showed that despite having a higher g₃₃, the magnetoelectric composite with the one-step 1,100 ℃ specimen exhibited the lowest magnetoelectric voltage coefficient, due to its lowest k_p. This study highlights the essential role of phase fraction and relative density in enhancing the performance of piezoelectric materials and devices, showcasing the effectiveness of the two-step sintering process for controlling the microstructure of ceramic materials containing volatile elements.