Specific heat properties of KH2PO4

Publisher Website
Google Scholar
Abstract
Calorimetric studies of KDP crystals are reviewed, and two categories of studies are involved: (1) Specific heat measurements near the transition temperature, and (2) specific heat measurements at low temperatures (0.1–30 K). Measurements near Tc confirm the first-order transition in KDP and correlate very well with dielectric data via the predictions of the free-energy expansion. Similar measurements on KDP-type isomorphous crystals confirm the order-disorder nature of the transition. At low temperatures KDP displays a maximum in c/T3 at 17 K associated with proton motions which may be the residual of the soft mode. An anomalous T 3/2 contribution to the specific heat appears below 5 K and depends on the size and purity of the crystal. This term is missing if the hydrogen bonds are disordered [i.e., as in the frustrated system Rb0.52(ND4)0.48D2PO4] and a glasslike linear term appears instead. An average calorimetric Debye temperature of 362 K for KDP is recommended. Suggestions are made for future calorimetric studies on KDP-type crystals.