Physical properties of piezoelectric oxides

在功能材料领域，压电、铁电和多铁性系统由于其潜在的应用，例如，作为传感器、电子存储器或超声换能器。这组晶体包括结晶为压电体或铁电体的氧化物化合物。到目前为止，压电或铁电氧化物的弹性性质已经在某些情况下作为温度的函数进行了研究，但在大多数情况下没有进行进一步的研究。这特别适用于温度相关的声阻尼现象。通过弹性张量的温度依赖性可以特别灵敏地测量机械性能的变化，即，的热弹性系数，并因此与超声技术的帮助。压电性能也可以使用超声技术，特别是共振超声光谱（罗斯），因为机电耦合与其弹性性能密切相关。该项目的目的是研究选定的氧化物晶体的弹性和压电性能（硅铝黄长石，钙铝黄长石，钙铝黄长石，γ-LiAlO 2，LiGaO2）使用罗斯技术作为温度的函数，以分析这些材料的弹性和热弹性行为的基本特征，材料在很宽的温度范围内。进一步加深对温度相关声阻尼现象以及晶体结构与热弹性性质相关性的理解。 由于弹性性质反映了晶体结构的三维键合系统，因此诸如罗斯的超声技术提供了用于检测结构不稳定性和相变的高灵敏度探针。结果将提供以下信息：（1）氧化物中可能发生温度依赖性声阻尼（例如钙铝黄长石、钙铝黄长石），（2）在与超声阻尼相关的高温范围内，在硅线石中是否发生显著的结构变化，以及（3）在超声波阻尼的温度极限以上直到熔点，硅线石的温度依赖性弹性和压电张量分量如何变化。另一个方面涉及的温度相关的增加锂扩散的γ-LiAlO 2和LiGaO 2（环境温度到熔点）和弹性和压电性能，以及可能发生的超声阻尼。为了阐明频繁发生的压电效应，高温电导率和HT-DK测量连同高温结构测定和温度依赖的粉末SHG测量的降低的可能原因将在这些化合物的一部分上进行。

In the field of functional materials, piezoelectric, ferroelectric and multiferroic systems have repeatedly been investigated in more or less detail in the past because of their potential applications, e.g., as sensors, electronic memories or ultrasonic transducers. This group of crystals includes oxide compounds that crystallize as piezoelectrics or ferroelectrics. Up to now, elastic properties of piezoelectric or ferroelectric oxides have been investigated in some cases as a function of temperature, but in most cases no further investigations have been carried out. This applies in particular to the temperature-dependent acoustic damping phenomena. The changes in mechanical properties can be measured particularly sensitively via the temperature dependence of the elasticity tensor, i.e., the thermoelastic coefficients, and thus with the aid of ultrasound techniques. The piezoelectric properties can also be derived using ultrasound techniques, in particular resonant ultrasound spectroscopy (RUS), as the electromechanical coupling is closely linked to their elastic properties.The aim of the project is to investigate the elastic and piezoelectric properties of selected oxidic crystals (sillenites, gehlenite, fresnoite, gamma-LiAlO2, LiGaO2) using the RUS technique as a function of temperature in order to analyze the basic features of the elastic and thermoelastic behaviour of these materials in a wide temperature range. Furthermore, the understanding of temperature-dependent acoustic damping phenomena and the correlation of crystal structure and thermoelastic properties will be deepened. Since the elastic properties reflect the three-dimensional bonding system of the crystal structure, ultrasound techniques such as RUS provide a highly sensitive probe for the detection of structural instabilities and phase transformations. The results will provide information on (1) the possible occurrence of temperature-dependent acoustic damping in the oxides (e.g. gehlenite, fresnoite) investigated here as was already observed for the sillenites, (2) whether a significant structural change occurs in the sillenites in the high-temperature range associated with the ultrasound damping, and (3) how the temperature-dependent elastic and piezoelectric tensor components of the sillenites change above the temperature limit of the ultrasound damping up to the melting point. Another aspect deals with the temperature-dependent correlation of increasing lithium diffusion of gamma-LiAlO2 and LiGaO2 (ambient temperature to melting point) and the elastic and piezoelectric properties, and a possible occurrence of ultrasound damping. In order to elucidate the possible reasons for a frequently occurring decrease of the piezoelectric effect, high-temperature conductivity and HT-DK measurements together with high-temperature structure determinations and temperature dependent powder-SHG measurements will be performed on a part of these compounds.