Piezoelectric Properties near the Tricritical Point on KF-Doped BaTiO3 Single Crystal

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The temperature dependence of the piezoelectric constant $d_{33}$, electromechanical coupling factor $k_{33}$, dielectric constant $\varepsilon_{33}^{\text{T}}$ and elastic compliance $s_{33}^{\text{E}}$ for a single crystal of KF-doped barium titanate with a KF content near the tricritical point (TCP), Ba0.91K0.09TiO2.91F0.09 (KF-BT/0.09), was measured by a resonance–antiresonance method in a temperature range between 270 and 340 K. The single crystals used were grown by a KF-flux method and the largest single crystal was a cube of 5 mm size. A large piezoelectric constant and a large dielectric constant were obtained at 300 K: $d_{33} = 300$ pC/N, $k_{33} = 0.59$, and $\varepsilon_{33}^{\text{T}} = 3{,}000$. As the temperature increases, $\varepsilon_{33}^{\text{T}}$ gradually increases toward $T_{\text{C}}$ but does not show any discontinuous changes at $T_{\text{C}} = 329$ K; moreover, $s_{33}^{\text{E}}$ and $d_{33}$ increase with temperature between 270 and 310 K. However, above 310 K, they decrease toward $T_{\text{C}}$. The fluctuation of the order parameter near the TCP induces these peculiar behaviors.
2009-09-25