Critical phenomena in potassium dihydrophosphate (KDP)
Zisman A.N., Kachinskii V.N., Stishov S.M.
The behavior of the linear coefficient of expansion and linear compressibility of KDP single crystals in the region of the ferroelectric phase transition at pressures to 4.5 kbar has been investigated for the first time by means of a capacitive dilatometer. Existence of the tricritical point with coordinates Tt = 109.8 + 0.2 К and P, = 2640 + 40 bar has been reliably established. It is shown that the behavior of the thermal expansion and compressibility in the case of KDP is adequately described by means of the Landau theory (index a = 0.5) under the condition that the coefficients in the Landau expansion are considered to be functions of pressure and temperature.