High Temperature LGT Expansion Measurements through Multiple Techniques

There is a pressing need for high performance sensors and signal processing devices to operate in hostile environments in many industries and forefront system applications, such as automotive, aerospace, and geo-surveying. These devices should reliably operate at temperatures between 300°C and 1200°C. Recently introduced piezoelectric crystals, such as langatate (LGT), opened up the opportunity of employing acoustic wave (AW) sensing technology for these harsh environment applications where access to the device is difficult or impossible while in high temperature operation. In order to design high temperature AW devices and take advantages of temperature compensated crystal orientations, or temperature sensitive crystal orientations, one needs to extract the AW properties of LGT, in particular at high temperature. One of the fundamental material properties are the thermal expansion coefficients. This thesis reports on the LGT thermal expansion measurements performed and compared using three techniques: dual push-rod differential dilatometry, x-ray powder diffraction, and optical differential dilatometry. The expansion measurements have been performed from room temperature to 1200°C along the crystalline X, Y, and Z axes, and from these measurements the thermal expansion coefficients have been extracted. In addition, the bulk density of LGT single crystal was measured and compared to the measured x-ray density as an indication of the crystal quality. The bulk density was determined with a hydrostatic weighing procedure using high purity water as a replacement for toxic and more expensive chemicals. The measurements performed confirmed the viability of utilizing high purity water for high precision density measurements