Hydrostatic Pressure Effect on the Ferroelastic Monoclinic Phase of [N(CH₃)₄]₂MCl₄ (M=Fe, , Zn)

抄録

The deviation of the monoclinic angle from 90°, Δβ, in the ferroelastic phase (space group P12₁/c1) of [N(CH₃)₄]₂MCl₄ (M=Fe, , Zn) has been measured as a function of hydrostatic pressure by X-ray diffraction method. The contour lines of the equal Δβ in the pressure-temperature phase diagram converge on the boundary between the normal (Pmcn) and ferroelastic phases, drawing arcs. Systematic feature among the isostructural [N(CH₃)₄]₂MX₄ (X=Cl and Br) compounds is discussed on the universality of the pressure-temperature phase diagrams.