Electron density distrubution and physical properties in chalcogenide ceramics semiconductors

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Symmetry of AgGaS_2 high-pressure phase has been determined by the single crystal method using a diamond anvil pressure cell. The crystal was monoclinic with space group Cc. Intensity data of a specimen in the diamond anvil cell were collected at 5.5 GPa, using a horizontal-type four-circle diffractometer at the beam line 14A, Photon Factory, KEK, with synchrotron radiation of 0.5 * wavelength. The structure has been determined from the three-dimensional X-ray diffraction data. The phase transition at 4.2 GPa was reversible. A most conspicuous structural feature accompanying the phase transition was a characteristic compression of one of the octahedral large interstices formed by sulfur atoms. It was also found that the difference of bonding nature between the ionic Ag-S and the more covalent Ga-S plays an important roll in the high-pressure phase transition. Development of the software to control the diffractometer for the high-pressure measurement has been undertaken. The performance of the diffractometers, including the four-circle diffractometers with Ag rotating anode, that with synchrotron radiation, and the two-axis diffractometer with the CCD area detector, were compared using a CuInSe_2 crystal, for more accurate structural investigation under high pressures. The structure of Cu_2In_4Se_7, a key material to govern the development of solar device based on CuInSe_2 was first solved in this study.