Evidence for Logarithmic Singularities in the Specific Heats of the Ferroelectric Crystals KH2PO4 and KH2AsO4

Abstract

By drawing interpolation curves between the high- and low-temperature branches of the specific heats of K${\mathrm{H}}_2$P${\mathrm{O}}_4$ and K${\mathrm{H}}_2$As${\mathrm{O}}_4$ (measured by Stephenson and co-workers) we have decomposed each specific-heat function into the sum of a monotonic term plus an anomolous term, peaked about the transition temperature. In the region of the transition temperature ${\theta }_c$ we find that the paraelectric and ferroelectric branches of the anomalous specific heat of each crystal have the limiting behavior $C^a=-A\ln |\theta -{\theta }_c|+B,$ where $A=1.2\mathrm{}\pm 0.3$ cal/mole deg, $B=0.95\mathrm{}\pm 0.07$ cal/mole deg for $\theta >{\theta }_c$, and $A=14.2\mathrm{}\pm 1.4$ cal/mole deg, $B=14.4\mathrm{}\pm 0.3$ cal/mole deg for $\theta <{\theta }_c$. These constants have the same values for both crystals.