High-temperature behavior of NH4H2PO4 studied by single-crystal and MAS NMR

To confirm a high-temperature behavior of NH4H2PO4, the temperature dependences of the line-width, resonance frequency, and spin–lattice relaxation times in the laboratory frame, T1, and in the rotating frame, T1ρ, were investigated using a Fourier transform NMR spectrometer. The hydrogen bonds both in O–H–O between two PO4 groups and in N–H–O between NH4 and PO4 were distinguished, and the T1 values of both types of hydrogen-bond proton and 31P ions were described by the Bloembergen–Purcell–Pound theory. In addition, the T1ρ values of both types of hydrogen-bond proton and of 31P ions exhibited strong temperature dependences at high temperature; the changes in T1ρ at high temperature were related to variations in the symmetry.

Graphical abstractTo confirm a high-temperature phase transition in NH4H2PO4, the temperature dependences of the line-width, resonance frequency, and spin–lattice relaxation times in the laboratory frame, T1, and in the rotating frame, T1ρ, were investigated using a Fourier transform NMR spectrometer.Figure optionsDownload full-size imageDownload as PowerPoint slide