Proton Magnetic Relaxation Study of Phase Transition in Crystalline p-Terphenyl

Abstract

Proton spin-lattice relaxation time T₁ was measured at 19.5 MHz of p-terphenyl in the vicinity of its solid-solid phase transition point. A sharp decrease in T₁ was observed near the transition point and was attributed to the critical fluctuation associated with the phase transition. The T₁ was interpreted successfully in terms of the order-disorder mechanism by which the central phenylene ring jumps between two stable sites in a double minimum potential well and its motion undergoes a critical slowing down in the phase transition region. The possibility of displacive phase transition was also discussed.