LARGE VOLUME CELL AT HIGH P/T- NEW LIMITS AND FUTURE PROSPECTS. W.Utsumi, Department of Synchrotron Radiation Facility Project Japan Atomic Energy Research Institute Tokai-mura, Naka-gun, Ibaraki 319-11, Japan

In contrast to the diamond anvil cell, multi-anvil apparatus are capable of maintaining stable high temperatures under high pressure owing to the larger sample volume. More than 14 years have passed since the first multi-anvil apparatus for synchrotron radiation was installed at the Photon Factory, and similar apparatus have been installed at the HASYLAB and NSLS. These multi-anvil systems combined with synchrotron radiation have brought us a large number of excellent results. The recent biggest advance in the multi-anvil apparatus is the use of sintered diamond as an anvil material. The characteristics of sintered diamond such as high compressive strength and no cleavage plane has enabled us to extend the attainable pressure range greatly. Many attempts have been made to replace tungsten carbide anvils with sintered diamond for the various type of multi-anvil apparatus, and most of them have had successful results.

Among the several multi-anvil type apparatus, the DIA type apparatus, a variation of cubic anvil press, has been most commonly used for the synchrotron radiation experiment in Japan. This system has many advantages; 1) fairly large sample volume which has a simple symmetry, 2) stable high pressure and high temperature generation. 3)quasi-hydrostaticity, 4) simple x-ray diffraction geometry. By use of sintered diamond anvils with 3mm truncation, the DIA can generate pressures up to 20GPa.

Recently, the octahedral compression system with sintered diamond anvils has made great progress. This system has now reached pressures over 30GPa and temperatures up to 2000C in a sample volume of about 1mm3. In situ x-ray observation using this system have been successfully made, and various experimental results have been obtained. In this system, sintered diamond is used as an x-ray window. The fact that high energy x-ray can pass through the sintered diamond made this technique possible.

Although it might not be called multi-anvil, the simple opposed anvil type apparatus still has some advantages. Taking a Drickamer type sintered diamond anvil cell for example, it can generate more than 50GPa, and in situ observation has been successfully made at high P-T condition. There are some unreliability of the data because of the small sample volume and strong deviatric stress, but the opposed anvil devices are also very useful when they are used properly depending on the purpose and condition of the experiment.

In my talk, I will review the current status on the technical development in multi-anvil apparatus, and show a conception design of a new high pressure apparatus for the third generation synchrotron radiation (SPring-8).