Acoustic loss and electromechanical properties of LiNb_(1-x)Ta_xO_3

该提案是“极性氧化物中的周期性低维缺陷结构”研究小组的一部分，该小组致力于利用铌酸锂-钽酸锂（LNT）模型系统研究缺陷结构、电子和离子输运以及机电性能的相关性。LNT固体溶液具有高热稳定性和高压电系数，这为高温下的压电结构开辟了广泛的新兴应用。后者需要了解点缺陷和畴壁的相互作用及其对机电性能的影响。确定相关现象，如声损失是这个子项目的主要重点。除了传统的压电单晶外，必须考虑到损耗机制还受固溶体组成和畴结构的控制。如果了解了损耗机制，这两个参数为定制晶体特性提供了许多选择。针对不同的应用领域，应确定合适的Nb/Ta比和畴结构。例如，对于高温致动器和传感器或声学晶体，尚不清楚哪种Nb/Ta比和畴结构同时导致高压电系数、高居里温度、低声损失和高热稳定性。研究计划从室温开始，在很宽的温度范围内进行。根据具体目的和研究方法的不同，居里温度或熔化温度代表上限。特别是，声学损失、畴和畴壁的电导率以及高温下的矫顽力场强应被确定，并与其他子项目的结果与固溶体组成、点缺陷的类型和密度、畴壁密度和电荷相关联，以便分配原子机制，如非弹性弛豫。基于这些见解，应该进一步研究如何将声损失最小化，以及是否可以通过掺杂或合适的域结构来实现。预期的研究方法，如共振超声光谱法、脉冲回波法、激光多普勒振动法和电化学（微）阻抗谱法，应在可变氧和Li2O分压下应用到至少1000°C的温度，并由机电特性建模支持。

The proposal is part of the research group "Periodic low-dimensional defect structures in polar oxides", which is dedicated to the correlation of defect structure, electron and ion transport and electromechanical properties using the model system lithium niobate-lithium tantalate (LNT).LNT solid solutions offer high thermal stability and high piezoelectric coefficients, which opens up a broad range of emerging applications for piezoelectric structures up to high temperatures. The latter requires the understanding of the interaction of point defects and domain walls as well as its effects on the electromechanical properties. The determination of related phenomena such as acoustic losses is the main focus of this subproject. Beyond conventional piezoelectric single crystals, it must be considered that the loss mechanisms are also governed by the composition of the solid solution and the domain structure. Provided that the loss mechanisms are understood, both parameters offer numerous options for tailoring the crystal properties. Favorable Nb/Ta ratios and domain structures shall be identified for different application fields. For example, for high temperature actuators and sensors or acoustic crystals, it is unknown which Nb/Ta ratios and domain structures result simultaneously in high piezoelectric coefficients, a high Curie temperature, low acoustic losses and high thermal stability.The investigations are planned in a wide temperature range starting at room temperature. Depending on the specific objective and the investigation method, the Curie temperature or the melting temperature represent the upper limit. In particular, acoustic losses, the electrical conductivity of domains and domain walls and the coercive field strength at high temperatures shall be determined and correlated in concert with the results of the other subprojects with the solid solution composition, the type and density of point defects and the domain wall density and charge, so that atomistic mechanisms such as anelastic relaxation can be assigned. Based on these insights, it should be further examined how the acoustic losses can be minimized and whether this can be achieved by doping or a suitable domain structure.The anticipated investigation methods such as resonant ultrasonic spectroscopy, pulse-echo method, laser Doppler vibrometry and electrochemical (micro-)impedance spectroscopy shall be applied up to a temperature of at least 1000 °C at variable oxygen and Li2O partial pressures and supported by modeling of the electromechanical properties.