87Rb spin–lattice relaxation study of the ferroelectric phase transition in RbH2PO4

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Abstract
The temperature dependences of the 87Rb laboratory (T1) and rotating frame (T1ρ) spin–lattice relaxation times were measured in RbH2PO4. The relaxation rates are determined by two competing effects: by a ’’fast’’ soft mode relaxation mechanism which dominates at lower temperatures near the ferroelectric transition, and by a ’’slow’’ high temperature motion mechanism which is rate determining above 220 °K. The soft mode spectrum was found to be flat between 18 and 320 kHz. The ’’uncorrelated’’ order parameter correlation time τa=4×10−13 sec at 200 °K is of the same order as in other KH2PO4 ferroelectrics.