Critical behavior of KDCO 3 from 2 H and 39 K single crystal NMR

Potassium hydrogenocarbonate KDCO 3 presents an order/disorder phase transition at T c ≈ 353 K. The critical behavior of this phase transition was studied by single crystal 2 H and 39 K NMR. The evolution of the order parameter as a function of temperature is quantified, and the critical exponent was determined, indicating a transition close to a tricritical point. The 2 H Zeeman relaxation rate is strongly increased near the transition temperature. By calculating the noncritical contribution to the Zeeman relaxation rate, we show that the observed relaxation rate clearly presents a pseudo‐divergent behavior near T c , with a logarithmic singularity. The nature of the phase transition is discussed in the light of these results. Copyright © 2007 John Wiley & Sons, Ltd.