Dielectric Study of the Ferroelectric Phase Transition in DMAGaS Crystal

Abstract

Electric permittivity measurments as functions of temperature at constant dc electric field and as functions of the dc electric field at constant temperatures in the paraelectric phase have been performed for DMAGaS crystal. The changes of the permittivity maximum with the electric field intensity evidence the first-order character of the ferroelectric phase transition at Tc1. The field dependence of the permittivity ε(E) in the paraelectric phase is discussed, using the classical electric equation of state. A method for the determination of the corresponding coefficients is proposed. The obtained B and C coefficients, together with double hysteresis loop observed above Tc1 prove the first-order character of the ferroelectric phase transition in DMAGaS crystal.

Order-disorder model of phase transitions in the dmagas-dmaals family crystals

“…(CH 3 ) 2 NH 2 Al(SO 4 ) 2 · 6H 2 O (DMAAlS) and (CH 3 ) 2 NH 2 Ga(SO 4 ) 2 · 6H 2 O (DMA-GaS) belong to is experimentally studied during the past decade. A peculiar feature of the family is a possible existence of the crystal in three different phases at change of temperature: at room temperature the crystal is paraelectric, at lowering of temperature it sequentially becomes ferroelectric and antiferroelectric (Pietraszko, Lukaszewicz and Kirpichnikova, 1993;Pietraszko and Lukaszewicz, 1994;Pietraszko, Lukaszewicz and Kirpichnikova, 1995;Tchukvinskyi, Cach and Czapla, 1998). For example, it has been measured T c1 = 136 K and T c2 = 113 K by Tchukvinskyi et al (1998) (or 122 K and 114 K correspondingly (Pietraszko et al, 1995)) for DMAGaS Figure 1: Projection of N and C atoms in the dimethylammonium groups of DMA-GaS crystal at ambient temperature (Pietraszko et al, 1993) onto the ac plane (the b coordinate is indicated for each atom; k is the index of DMA sublattices).…”

“…crystal, but it has been only found T c1 = 150 K (Pietraszko et al, 1993;Pietraszko et al, 1994;Pietraszko et al, 1995) for DMAAlS. The phase transition between the ferroelectric and antiferroelectric phases is of the first order (Pietraszko et al, 1995;Tchukvinskyi et al, 1998). There are evidences, supplied by optical, ultrasonic, pyroelectric, dilatometric and dielectric measurements, that the phase transition paraelectric -ferroelectric is of the first order close to the second one in DMAGaS and of the second order in DMAAlS.…”

Microscopic model of phase transition in the crystals of the DMAAlS and DMAGaS types

“…It has been measured T c1 = 136 K and T c2 = 113 K [4] (or 122 K and 114 K respectively [3]) for DMAGaS crystal, but it has been only found T c1 = 150 K [1,2,3] for DMAAlS. The phase transition between the ferroelectric and antiferroelectric phases is of the first order [3,4].…”

“…A peculiar feature of isomorphous crystals with ferroelectric properties (CH 3 ) 2 NH 2 Al(SO 4 ) 2 • 6H 2 O (DMAAlS) and (CH 3 ) 2 NH 2 Ga(SO 4 ) 2 • 6H 2 O (DMAGaS) is the possibility of existence in three different phases at change of temperature: at room temperature crystal is paraelectric, at lowering of temperature it sequentially becomes ferroelectric and further can be in antiferroelectric state [1,2,3,4].…”

Dielectric properties of a DMAGaS/DMAAS mixed crystal

“…Both crystals exhibit a structural transition into a ferroelectric phase. The ferroelectric transition is thought to be of the order-disorder type [2,3,6,7]. However, in contrast to most of the representatives of hydrogen-bonded ferroelectrics, the driving force for the ferroelectric transition seems to be the ordering process of the dimethylammonium cations rather than that of the protons in the hydrogen bond system [7,8].…”