Determining Elastic Constants of Potassium Lithium Tantulum Oxide (KLT)

KLT is a ferroelectric relaxor crystal that has applications in optics and modern digital storage strategies. Determining the elastic constant C11 as a function of temperature is highly desirable for engineering applications. Through liquid nitrogen cooling and ultrasonic pulse echo methods, I find the temperature-elastic constant relationship for three varying lithium concentration samples.

The Sample

I paste 30 MHz sensitive transducers to each side of the sample and then mount the sample to a copper plate.

Cooling to 65 K

I insert the copper mounted sample into a brass tube, vacuum pump the air out, and add helium. This allows the sample to cool to lower temperatures with minimal disturbances. I then dip the sample into liquid nitrogen slowly.

The Input and Output Wave Form

As the sample cools, I send a pressure wave through the sample at 1 μs periodicity to determine the speed of sound through the sample at varying temperatures. The output waveform can be seen echoing through the sample in the image on the left.

Results

These are the results for 20%, 10%, and 1% Lithium concentration KLT samples (bottom to top). The ferroelectric behavior is characterized by the nonlinear elastic constant relationship with temperature. I conclude that the higher the lithium concentration, the further the crystal strays from obvious elastic constant dependency on temperature