[S-IT20] Deep Earth Sciences

[SIT20-P04] GHz-DAC ultrasonics: Current status and characteristics of the ZnO piezoelectric oscillator

*Akira Yoneda¹, Ryosuke Matsui¹, Ryoma Ishida¹, Hidenori Terasaki², Izumi Mashino³, Daisuke Yamazaki³, Tadashi Kondo¹ (1.Department of Earth and Space Science, Osaka University, 2.Graduate School of Natural Science and Technology, Okayama University , 3.IPM, Okayama Univ)

Keywords:GHz ultrasonics, Diamond anvil cell, lower mantle, ZnO transducer

We have developed a GHz ultrasonic technique to measure elastic velocities of thin samples (a few dozen mm) squeezed in a diamond anvil cell (DAC) up to ~67 GPa. We have devised (1) to construct GHz buffer rods, (2) to improve acoustic coupling between buffer rod and diamond anvil, (3) to improve SN ratio in measurement, and (4) to estimate the most probable travel time. We conducted a preliminary test with polycrystalline MgO; the consistency with previous studies suggests future potentiality of the GHz-DAC ultrasonics. Followingly, we succeeded to measure P wave travel time of e iron and S wave travel time of ferropericlase over 30 GPa pressure range. We succeeded to extend the pressure range to 67 GPa in ferropericlase measurement.
On the other hand, we examined the ZnO piezoelectric transducer between YAG crystal and an electrode. We learned that the ideal electrode should have twice the acoustic impedance of current electrode of indium.