Phase transitions in layer structured (C₁₀H₂₁ NH₃)₂SnCl₆

Phase transitions in the quasi-two-dimensional layer structured (C₁₀H₂₁NH₃)₂SnCl₆, an order-disorder transition and a conformational transition of the hydrocarbon chains, were studied by means of ₁H NMR (nuclear magnetic resonance). A newly defined order parameter in the low-temperature phase, the dipolar splitting of the rigid hydrocarbon lineshape component, was shown to represent the order-disorder motion of the hydrocarbon chains, explicitly revealing its three-dimensionality. The conformational transition was marked by a discontinuity in the spin-lattice relaxation rate (1/T₁). On the other hand, no obvious anomaly was observed in the spin-lattice relaxation rate at the order-disorder transition at 200 MHz, whereas a weak anomaly was observed at 45 MHz, indicating that the critical dynamics associated with the order-disorder transition is manifest in the low-frequency region of the spectral density.