1H NMR Measurements of the Phase Transition of (NH₄)₃H(SO₄)₂ Single Crystals

다국어 초록 (Multilingual Abstract)

$^1$H nuclear magnetic resonance (NMR) experiments have been
performed in the temperature range of 30 -- 300 K at 7 T to
investigate the phase-dependent nature of the dynamic network of
hydrogen bonds in a ((NH₄)₃H(SO₄)₂ single crystal. The
crystal has six phases, which are ferroelectric, antiferroelectric,
incommensurate, antiferroelectric, ferroelastic, and superionic with
the respective transition temperatures of 63, 133, 139, 256 and 413
K. The spin-lattice relaxation time, T₁, of ¹H NMR is similar
for the ammonium protons and the hydrogen-bond protons over the
entire range of experimental temperatures. The T₁, of ¹H NMR
gradually decreases down to 120 K and starts to steeply increase
below 100 K. Then, the T₁ shows an abrupt decrease below 68 K
with a sharp minimum at 63 K, where the ferroelectric transition
occurs. The ¹H NMR spectrum shifts to the high-frequency side at
temperatures below 63 K due to the ferroelectric phase transition.
This behavior of the T₁ and the spectrum confirms a dramatic
change in the dynamics of hydrogen bonds associated with the
ferroelectric phase transition at 63 K.

다국어 초록 (Multilingual Abstract)

$^1$H nuclear magnetic resonance (NMR) experiments have been
performed in the temperature range of 30 -- 300 K at 7 T to
investigate the phase-dependent nature of the dynamic network of
hydrogen bonds in a ((NH₄)₃H(SO₄)₂ single crystal. The
crystal has six phases, which are ferroelectric, antiferroelectric,
incommensurate, antiferroelectric, ferroelastic, and superionic with
the respective transition temperatures of 63, 133, 139, 256 and 413
K. The spin-lattice relaxation time, T₁, of ¹H NMR is similar
for the ammonium protons and the hydrogen-bond protons over the
entire range of experimental temperatures. The T₁, of ¹H NMR
gradually decreases down to 120 K and starts to steeply increase
below 100 K. Then, the T₁ shows an abrupt decrease below 68 K
with a sharp minimum at 63 K, where the ferroelectric transition
occurs. The ¹H NMR spectrum shifts to the high-frequency side at
temperatures below 63 K due to the ferroelectric phase transition.
This behavior of the T₁ and the spectrum confirms a dramatic
change in the dynamics of hydrogen bonds associated with the
ferroelectric phase transition at 63 K.

참고문헌 (Reference)

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