[S-IT20] 地球深部科学

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

*米田 明¹、松井 亮介¹、石田 涼真¹、寺崎 英紀²、増野 いづみ³、山崎 大輔³、近藤 忠¹ (1.大阪大学理学研究科宇宙地球専攻、2. 岡山大学自然科学研究科、3.岡山大学惑星物質研究所)

キーワード：GHz音速法、ダイヤモンド・アンビル・セル、下部マントル、ZnO圧電素子

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.