抄録
The long range order parameter of the β’AuZn alloy of the L20-type structure has been measured by X-ray diffraction at temperatures ranging from 200°C to 650°C, the latter temperature being 75°C below the melting point Tm. Relative intensities of several h00 type reflections from single crystals have been measured using a counter diffractometer equipped with a high temperature attachment. It has been observed that the order parameter gradually decreases with rising temperature but appears to keep an appreciably high value at Tm. An abnormal increase in the lattice spacing has also been observed at about 550°C, which corresponds to the onset of an appreciable disordering detected by the intensity measurement. It is concluded that β’AuZn is a special type of ordered alloy and it would undergo a transition into the disordered alloy state, if it were not melted.
The root-mean-square displacement of atoms due to thermal vibration has been measured as a function of temperature. At room temperature the displacement is 0.125Å, 4.6% of the nearest neighbor distance, and increases to 0.255Å at 650°C.
