Dielectric and Electrooptic Properties of the DMAMeS (Me = Al, Ga) Crystals in the Region of Low Temperature Phases

Abstract

This paper presents the results of investigations of the dielectric, birefringent and electrooptic properties of NH 2 (CH 3 ) 2 Me(SO 4 ) 2 Á 6H 2 O (Me ¼ Al, Ga) crystals. The data obtained are compared with the predictions of a phenomenological theory. In particular, the temperature behaviour of the dielectric susceptibility components and their anomalies in the vicinity of phase transition points were investigated in details. The specific behaviour of the studied parameters in the low temperature region was related to the coexistence of ferroelectric and antiferroelectric ordering of the dimethylammonium groups carrying a dipole moment. phys. stat. sol. (b) 228, No. 3, 785-798 (2001) # WILEY-

Gaussian Fluctuations of Polarization in the Region of Phase Transitions in Dmagas-Dmaals Ferroelectrics in the Framework of the Four-State Model

“…Each DMA group can be oriented in four different ways; the orientational states differ in pairs in their energy. The results obtained in the mean field approximation (MFA), such as the temperature behaviour of spontaneous polarization, the changes in occupation of the orientational states and phase diagrams [5], are in satisfactory agreement with the experimental data [2][3][4]6]. The effect of suppression of the ferroelectric phase in DMAGaS under the influence of hydrostatic pressure [7] was also explained by the model.…”

Dielectric and spectral properties of DMAAS ferroelectric crystals doped with chromium

“…Crystals of dimethylammonium aluminum sulfate hexahydrate NH 2 (CH 3 ) 2 Al(SO 4 ) 2 × 6H 2 O (DMAAS) have been widely studied recently using different experimental methods [1][2][3][4][5][6][7].…”

“…At T c1 = 152 K the crystal undergoes a phase transition involving a reorientation of dimethylammonium cations, the structure becomes fully ordered and macroscopic polarization appears [6,9]. In the works [3][4][5] there were found anomalies of the dielectric and optical parameters at T c2 = 110,5 K and T 1 = 75 K. The low temperature anomaly was supposed to be related to the transition into the antiferroelectric phase whereas the temperature region between T c2 and T 1 was proposed to be characterised by a co-existence of ferroelectric and antiferroelectric phases [5]. An additional phase transition of this system at 390 K was suggested based on the analysis of optical absorption edge in UV [10].…”

Peculiarities of domain structure and the formation process of nano- and microcrystals on the surface of [NH2(CH3)2]Al0.8Cr0.2(SO4)2×6H2O single crystals

“…З пониженням температури кристал зазнає фазового переходу другого роду з параелектричної (сеґнетоеластичної) фази, якщо T c = 152 К, у сеґнетоелектричну фазу [3]. Цей фазовий перехiд належить до типу впорядкування зi змiною симетрiї 2/m → m. Перехiд пов'язаний з упорядкуванням полярних катiонiв DМА, що здiйснюють обертання навколо напряму C-C в параелектричнiй фазi i впорядковуються тiльки за просторово-часового усереднення в сеґнетоелектричнiй фазi [8,9].…”