Critical Dielectric Relaxation in Ferroelectric Betaine Phosphite in the Microwave Region

Abstract

The dielectric behaviour of ferroelectric hydrogen‐bonded betaine phosphite crystals is investigated in the frequency range up to 77 GHz. The dielectric dynamics of Debye‐type shows a critical slowing‐down of the polarization fluctuations. The frequency of the relaxational soft mode in the paraelectric phase varies according to vs = 0.36(T‐218) GHz and decreases to 2.4 GHz at Tc = 224 K. The calulated activation energy for flipping proton motion ΔU = 2.7kTc shows the order‐disorder character of the proper ferroelectric phase transition.

Crossover between ferroelectric order and dipolar glass disorder in betaine phosphate0.06betaine phosphite0.94mixed crystals

“…At lower frequencies (be low 1 GHz) in BPI an additional dielectric dispersion was observed, which is obviously related with dynam ics of ferroelectric domains [11]. Close to the ferro electric phase transition, the spontaneous polariza tion was observed in BPI [12]. A similar behaviour of dielectric dispersion was observed in BP crystals [13].…”

“…Different approaches can be used to de scribe the temperature behaviour of the spontaneous polarization of ferroelectrics. According to the Ising model [12] . (10) Moreover, according to this model the transition temperature T C Ising is determined by the condition .…”

“…This becomes understandable from the below presented experimental results that the spontaneous polarization shows a remarkable distribution. The qua sionedimensional Ising model presupposes homoge neity [12] and cannot describe the nonhomogeneous ferroelectrics. However, in nature crystals (including ferroelectrics and the same "pure" betaine phosphite) without impurities do not exist.…”

Dielectric Dispersion in Ferroelectric Glycine Phosphite

“…The dielectric permittivity fulfills the Curie-Weiss law with the Curie constant Cp = 375 K in the paraelectric phase in temperature region of about 20 K above the Curie point. The constant C, is much smaller than that for another hydrogen bonded crystal of BPI (betaine phosphite) containing phosphite anions chains [9,10].…”

Ultrasonic Anomalies in Deuterated Betaine Phosphite near the Ferroelectric Phase Transition

“…At T c1 355 K, BPI undergoes an order±disorder phase transition into a ferroelastic phase with space group P2 1 /c where the unit cell doubles along the c-axis [6]. On further cooling, the crystal then undergoes a transition of second order into a ferroelectric phase with the space group P2 1 [5,7] at T c 216 K. Studies of the dynamic dielectric properties of BPI crystals [8] showed that the dielectric dispersion is of Debye-type with the frequency of the soft relaxational mode n s 0X36T-218) GHz in the paraelectric phase.…”