Neutron diffraction study of quantum effects on structural phase transition in quartz

Hayashi, Makoto*; Fujishita, Hideshi*; Kanai, Takashi*; Yamada, Takahiro*; Igawa, Naoki   ; Kihara, Kuniaki*

A phenomenological theory describes the temperature dependence of the order parameter Q, which is atomic shift in displacement structural phase transition and of strain e, which is coupled to Q, near a phase transition. Recently, Romero and Salje showed the strain obeys the quantum phenomenological theory below the temperature of the displacement structural phase transition. However, direct evaluation of the quantum phenomenological theory by measuring the order parameters in entire temperature is required to verify the effectiveness of the theory. We carried out the structural analysis of quartz by neutron powder diffraction in the temperature range of 10-250K. We found that the strain was in proportion to the squares of the displacement of the Si atom along the a-axis in the present temperature range. The effectiveness of the theory was directly verified by the atomic displacement.