Piezoelectric resonance spectroscopy was used to evaluate the face shear piezoelectricity and its relaxation for structurally controlled poly-l-lactic acid (PLLA) films. We prepared samples by uniaxial drawing at 80 °C for a ratio of 2–6 and annealed at temperatures above glass transition (T_g = 60 °C) to below melting (T_m = 170 °C) for 1 hour. The degrees of crystallinity X_c and orientation F_c by X-ray diffraction were controlled over a broad range to reach X_c = 0.8 and F_c = 0.9. We measured broadband dielectric spectra where the piezoelectric resonance was observed superimposed on dielectric relaxation. Analyses of the resonance spectra for 45°-cut square sample resulted in the determination of the face-shear piezoelectric constants e₁₄ and d₁₄, as well as the elastic shear compliance s₄₄ and stiffness c₄₄. At room temperature, e₁₄ was shown to be proportional to a product of X_c*F_c, whereas d₁₄ demonstrated saturation due to an increase in c₄₄. By extrapolating to X_c*F_c = 1, the e₁₄^c = 27 mC/m² of PLLA crystal was determined. As the temperature increases, piezoelectric relaxation due to non-crystalline segmental motion was observed as well as dielectric and elastic relaxation. It was found that e₁₄ decreased in a similar manner to c₄₄ whereas d₁₄ increased slightly with increasing temperature. The temperature dispersions of e₁₄, d₁₄ and c₄₄ were reproduced using an equivalent three-spring model consisting of a crystalline piezoelectric spring connected by series and parallel non-crystalline relaxational springs based on the temperature-frequency reduction rule and the VTF-type dielectric relaxation time. The findings revealed key information on the ratio of noncrystalline phases connected in series and parallel to the oriented crystalline phase.

压电共振光谱用于评估结构控制的聚乳酸 (PLLA) 薄膜的面剪切压电性及其弛豫。我们通过在 80 °C 下以 2-6 的比例单轴拉伸制备样品，并在高于玻璃化转变温度 ( T _g  = 60 °C) 至低于熔点 ( T _m  = 170 °C) 的温度下退火 1 小时。X射线衍射的结晶度X _c和取向F _c被控制在很宽的范围内，达到X _c  = 0.8和F _c = 0.9。我们测量了宽带介电光谱，其中观察到压电共振叠加在介电弛豫上。对 45° 切割方形样品的共振谱的分析确定了面剪切压电常数e ₁₄和d ₁₄，以及弹性剪切柔量s ₄₄和刚度c ₄₄。在室温下，e _14与X _c * F _c的乘积成正比，而d ₁₄由于c _{44的增加而表现出饱和}. 通过外推到X _c * F _c  = 1，确定了PLLA晶体的e ₁₄ ^c  = 27 mC/m ²。随着温度的升高，观察到由于非晶段运动引起的压电弛豫以及介电和弹性弛豫。发现e _14以与c ₄₄相似的方式降低，而d ₁₄随着温度升高略有增加。e ₁₄ , d ₁₄和c ₄₄的温度分布使用等效三弹簧模型再现，该模型由基于温度-频率降低规则和 VTF 型介电弛豫时间的串联和并联非晶态弛豫弹簧连接的晶体压电弹簧组成。研究结果揭示了非晶相与定向晶相串联和并联的比例的关键信息。