X-Ray Study of Modulated Structure in [N(CH₃)₄]₂CuCl₄ under High Pressure

Abstract

Pressure–temperature dependence of modulation wavenumber of [N(CH₃)₄]₂CuCl₄ was measured with X-ray diffraction method in the region of 22≤T≤160°C, 0.25≤p≤0.95 GPa. Two commensurate phases with modulation wavenumber q=3⁄8 and 2⁄5 were found within the pressure-induced incommensurate phase. The phase q=3⁄8 is identified as the high-pressure ferroelectric phase F₂ found by Gesi.