LOW TEMPERATURE STUDY---NEW RESULTS AND FUTURE PROSPECT. Kazuhiko Tsuji, Department of Physics, Keio University, 3-14-1, Hiyoshi, Yokohama 223, Japan

An apparatus for X-ray diffraction measurements at high pressures and low temperatures using synchrotron radiation was constructed on a bending-beamline at the Photon Factory, KEK. It consists of a diamond anvil cell(DAC) in a cryostat, a two-dimensional detector of imaging plate, and an in-situ pressure measuring system of ruby fluorescence method.

Low temperature X-ray diffraction measurements under pressure are important for studies of kinetics of pressure-induced phase transitions, magnetic and dielectric phase transitions etc. In the experiments, however, there are some difficulties: (1) A position of the sample moves due to the thermal contraction with temperature. (2) For optical measurements of ruby fluorescence, a distance from the sample to a objective lens is long because of presence of thermal shields and optical window in the cryostat. (3) Size of the sample in DAC is small. Therefore, a special design for x-ray and optical measurements is needed.

X-ray from the bending magnet of BL-18C is monochromatized by Si(111) crystals and is focused by two mirrors of Pt-coated quartz. It impinges a sample between anvils. Diffracted x-ray goes through a window on the cryostat and is detected by the cylindrical or flat imaging plate with a positional resolution of 100 micrometers. By integrating the intensity over a wide area along Debye ring, more precise data can be obtained.

The DAC in the cryostat is cooled using a He refrigerator. Pressure in the sample can be changed by controlling the He gas pressure in a diaphragm which pushes a piston in the DAC. For pressure measurements, ruby fluorescence excited by an Ar ion laser through an optical fiber is collected by two lenses and is focused onto the end of a light fiber whose other end terminates at the entrance slit of a spectrometer. A CCD detector is used for a rapid data acquisition.

Studies on the temperature dependence of pressure-induced phase transitions including amorphizations for several semiconductors are in progress. Performance of the apparatus and new results will be reported.