As sensors, actuators and interconverters of mechanical signals into electrical quantities, piezoelectric materials are used in a wide range of industrial and laboratory settings. Currently, some of the most widely used piezoelectric materials are those with high piezoelectric responses, but their usefulness only extends over a relatively small temperature range, as at temperatures as low as ~ 200°C such materials depole or lose their piezoelectric activity. Recently, various industrial sectors have expressed the need for the use of piezoelectric devices in high temperature environments (> 200°C), where the piezoelectric materials are also required to have a high piezoelectric response. For the development of such piezoelectric materials insight into their dynamic electrical properties is required, which can be monitored, for example, by measuring the dielectric response at low frequencies (< 1 kHz). Such measurements can be performed by dedicated, commercially available measurement systems, however, efforts to identify high temperature piezoelectric materials sweep a broad range of chemical compositions, structures and properties, thus a novel measurement device was envisaged that could cater to the diverse range of materials properties that need to be explored. This master’s thesis presents the development of a measurement system that enables an automated high-temperature and low-frequency characterization of dielectric materials in the frequency range between 2 mHz and 1 kHz and in the temperature range from room temperature and 450 °C. The following requirements have been defined for the system: i) affordability, ii) high accuracy and iii) flexibility in terms of characterization of various dielectric samples of different dimensions and shape.
Based on a thorough examination of the advantages and disadvantages of the available methods of dielectric spectroscopy, in the first part of the thesis we determined the appropriate method for the low-frequency dielectric characterization. In the central part of the thesis, we explain the development of the measurement system, from the existing electronic devices and components, their working principles the related advantages and disadvantages, and their purposes in the developed measurement system. Furthermore, we present a computer software, that was designed within the scope of this thesis to cater to the unique requirements of the equipment and its operation. The software allows for fully automated measurements of the dielectric permittivity as a function of temperature, frequency and amplitude, and incorporates innovative design features that assist with minimizing experimental error and increase the overall accuracy of the measurements. In the final part of the thesis, we present the characterization and testing of the developed measurement system, which allowed us to verify the quality and the accuracy of the system as well as possible improvements. For this purpose, we have measured various dielectric samples at ambient and elevated temperatures and compared the measurement results with a reference measurement system and literature data.
Within this work we characterized a standard capacitor (for professional use) using the developed measurement system. We have confirmed that the measured values of the phase shift (frequency range of 2 mHz–100 Hz) are within the range defined by the capacitor manufacturer and that the measured values of the capacitance are within the defined tolerance of 1 %.