Evidence of Incommensurate-Ferroelastic (Commensurate) Phase Transition in {N(CH₃)₄}₂CuCl₄ Crystal

Abstract

Successive phase transition in {N(CH₃)₄}₂CuCl₄ has been studied by polarization microscopic observation and by the measurement of dielectric constant. A new phase transition is found to take place at intermediate temperature (about 8°C on cooling, about 18°C on heating) between the two phase transition points at 24°C and −9.4°C previously reported. Evidence is presented that the phase transition is the one from an incommensurate phase to a ferroelastic (commensurate) phase.