Electromechanical Properties of $PbTiO3$ Ceramics Containing La and Mn

A piezoelectric ceramic material having low dielectric constant, high thickness coupling factor, high mechanical quality factor, high stability, and high operating temperature, has been prepared from $PbTiO3$ incorporated with 2.5 mol% of $LaO12$ and 1.0 mol% of $MnO2$⁠. Typical electromechanical constants of this material are as follows: dielectric constant $ε11T/ε0 230, ε33T/ε0 170$⁠; coupling factor k₃₃ 0.46, k_t 0.46, k₁₅ 0.28, k_p 0.07, k₃₁ 0.04; mechanical quality factor Q 1100, Poisson's ratio σ^E 0.20. Frequency constants N_t and N_3t of the fundamental and third‐harmonic thickness vibrations have temperature coefficients of −1.1 × 10⁻⁴°C⁻¹ and −2 × 10^−5°C⁻¹, respectively. Aging rates of N_t and N_3t, are +0.02% and −0.02%/time decade at 30°C, respectively. The Curie point of this material exists at 470°C, and k₃₃ and k_t increase gradually with temperature up to 400°C. This material has grain size of 2–3 μ and bending strength of 2 × 10⁷ kg/m², and can be polished into very thin plate. The $PbTiO3$ ceramics have a high potential for use in electromechanical devices at high frequency and high temperature.