Pressure generation in a 6-8-2 type multi-anvil system: a performance test for third-stage anvils with various diamonds

Abstract

We developed a 6-8-2 cell for multi-anvil apparatus, where a pair of diamond rods are used as a pressure intensifier. We tested single crystal diamond (SCD), conventional sintered diamond (SD), and nano-polycrystalline diamond (NPD) as the third-stage anvils for the 6-8-2 system. In situ X-ray diffraction experiments were conducted to test the performance of the present cell, and pressure generation of ∼ 90 GPa was confirmed at a press load of 700 tons at room temperature, regardless of the difference in anvil material. Upon the heating of the sample, however, the pressure substantially dropped with increasing temperature>800 K when SCD and SD were used as third-stage anvils, and ultimately decreased to 20–30 GPa at 1400 K due to significant plastic deformation of the anvils. In contrast, pressures of 80–90 GPa were maintained at temperatures up to ∼ 1250 K when the NPD anvils were used. The pressure decreased significantly at still higher temperatures, but remained higher (∼ 55 GPa, at 1400 K) than those observed by using SCD and SD anvils. The plastic deformation of the NPD anvils was obviously smaller than that of the other anvils, suggesting that NPD is the most suitable anvil material for the 6-8-2 system.