Poling Field Dependence of Piezoelectric Properties and Hysteresis Loops of Polarization versus Electric Field in Alkali Niobate Ceramics

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The DC poling field dependence of piezoelectricity was investigated to evaluate the mechanism of domain alignment in lead-free ceramics of the form of ($1-x$)(Na,K,Li,Ba)(Nb0.9Ta0.1)O3–$x$SrZrO3 ($x=0--0.07$) by comparison with those of Pb(Zr,Ti)O3 (PZT), PbTiO3 (PT), and BaTiO3 (BT) ceramics. Poling was conducted at 150 °C for 30 min while varying the poling field ($E$) between $\pm 4.0$ kV/mm. By increasing $x$ from 0 to 0.07, the relative dielectric constant ($\varepsilon_{\text{r}}$), electromechanical coupling factor in the planar mode ($k_{\text{p}}$), frequency constant in the $k_{\text{p}}$ mode ($\mathit{fc}_{\text{p}}$), and piezoelectric strain constant ($d_{33}$) vs $E$ plots showed domain clamping at a specific $E$. $E$ was the coercive field estimated from the DC poling field dependence. The changes in $\varepsilon_{\text{r}}$, $k_{\text{p}}$, $\mathit{fc}_{\text{p}}$, and $d_{33}$ with $E$ became smaller at $x=0.06--0.07$, because of the proximity to the paraelectric phase. The ceramics with $x=0$, such as PT or BT ceramics, show similar $\varepsilon_{\text{r}}$, $k_{\text{p}}$, $\mathit{fc}_{\text{p}}$, and $d_{33}$ vs $E$ plots. The maximum $k_{\text{p}}$ (48%) and $d_{33}$ (307 pC/N) were obtained for $x=0.05$ with the lowest $\mathit{fc}_{\text{p}}$ of 2964 Hz$\cdot$m, as shown in the $\varepsilon_{\text{r}}$, $k_{\text{p}}$, $\mathit{fc}_{\text{p}}$, and $d_{33}$ vs $E$ plots for ceramics such as tetragonal hard PZT ceramics. Since domain alignment in the ceramics was accompanied by the deformation of crystals as a result of applying the poling field, it was clarified that the lead-free ceramics must have a high $k_{\text{p}}$ and high $d_{33}$ to realize a low $\mathit{fc}_{\text{p}}$, which corresponds to a low Young’s modulus. In addition, the optimal ceramic composition was obtained in the typical domain-clamping state from the poling field dependence. Furthermore, it was found that a higher $k_{\text{p}}$ was realized at a larger remnant polarization and a smaller coercive field in a symmetrical hysteresis loop of polarization vs electric field ($P$–$E$ hysteresis loop), because of the easy alignment of ferroelectric domains by applying a poling field. The results of the poling field dependence were also supported by results of expansion strain measurement.
2009-09-25

Poling Field Dependence of Piezoelectric Properties and Hysteresis Loops of Polarization versus Electric Field in Alkali Niobate Ceramics

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