Critical slowing down in betaine phosphate as studied by nuclear magnetic relaxation

Abstract

Proton and phosphorus spin-lattice relaxation time (T₁) measurements were applied to study the antiferroelectric phase transition in betaine phosphate (CH₃)₃NCH₂COO·H₃PO₄ at 86 K. In the whole temperature range studied, the T₁ or ¹H was governed by a dipolar fluctuation caused by the methyl- and the whole butyl-group reorientations. In the vicinity of the phase transition the T₁ of ³¹P shows a sharp dip which is a characteristic of critical slowing down. The analysis of the T₁ based on the order-disorder mechanism with respect to the position of the acidic protons leads to the critical exponent for the correlation length v=0.5.