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Abstract
The line width of the ν4 internal mode of Rb3D x H1-x (SeO4)2 was measured as a function of temperature from 295 to 15 K. The broadening of the line width was found as temperature approaches Tc . According to the motional narrowing theory developed in nuclear magnetic resonance technique, the line broadening Δ due to the phase transition is proportional to the characteristic time τ c of hydrogen (or deuteron) motion in the paraelectric phase. The slope of 1/Δ vs temperature becomes steeper with decreasing x, showing that the length of a hydrogen bond shortens and, in turn, the barrier height of a double minimum potential lowers. The change of the gradients of 1/Δ was found around 50 K for low x crystals and is discussed in relation to the zero point vibration.