A Structural Phase Transition in Superionic Conductor Ag_3SI

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The phase transitions and the crystal structures of a superionic conductorAg3SI were investigated by specific heat measurements and by X-ray as well asneutron diffraction methods. The transition entropies were measured to be 1.44cat/mol'deg for the y-f3 transition at 157Kand2.71 cat/mol-deg for the fi-x transi-tion at 519 K. The least squares refinements of atomic positions and isotropictemperattu'e factors were carried out. /7-Ag3SI is cubic with space group Pm3m inwhich Ag is distributed into four positions apart 0.5 A from the face centeredposition toward [100], while in 7-Ag.SI below 157 K, Ag is located at one ofthese four positions obeying the symmetry of the rhombohechal space group R3.From these experimental results, it was found that the nature of the successivephase transitions in Ag,81 was not only of the order-disorder type but also ofa structural phase transition. A comparison was made with the phase transitionof CsPbCl,.
社団法人日本物理学会の論文
1979-10-15