Dielectric properties and electric conductivity of dimethylammonium tetrachlorcobaltate ferroelectric crystals

Abstract

The dielectric parameters and electric conductivity of (NH2(CH3)2)2CoCl4 crystals are investigated. Existence of the ferroelectric phase was observed below Tc = 258 K. The occurrence of phase transitions at 244, 314, and 435 K is confirmed. The investigated crystals also manifest anomalously high conductivity commensurate with that in semiconductors. Its value as well as region of existence strongly depend on the preceding history of the sample. It is shown that the anomalous conductivity is connected with translocation of protons which participate in the formation of hydrogen bonds.

Investigations of High Temperature Phase Transitions in (NH3c2H5)2CuCl4Crystals

“…Unfortunately, it is difficult to investigate in detail the dielectric relaxation process because of very narrow region of existence of phase II. Nevertheless, one can note that determined value of Ea is higher than in related compounds with alkylammonium-cation (Ea = 0.340 eV for (NH2(CH3)2)2CoCl4 [9] and Ea = 0.355 eV for NH2(CH3)2MnCl3 •2H20 [8]), first of all, due to larger energy barrier between two different H-bonds [2].…”

“…The temperature dependence of a manifests clear anomalies at the temperatures limiting mentioned phase (with accounting of the temperature hysteresis). One can note that observed comparatively high conductivity by their value even exceeds the conductivity in known protonic conductor such as (NH2(CH3)2)2CoCl4 [9].…”

“…In the same time, study of the low frequency conductivity presents special interest since the investigated crystals containing the hydrogen bonds in their structure would manifest considerable protonic conductivity [9,10].…”

The Permittivity and AC Conductivity of the Layered Perovskite [(CH3)(C6H5)3P]2HgI4

“…In addition to their technological importance in numerous electrochemical devices, such as fuel cells and chemical sensors [4], these materials provide good models for transport in biological systems [5]. Among these materials are compounds of the type [(CH 3 ) 4 X-ray diffraction studies showed that the tetramethylammonium salts [(CH 3 ) 4 N] 2 MX 4 , and tetramethylphosphonium salts, [(CH 3 ) 4 P] 2 MX 4 , are isostructural with the P121/c1 phase at room temperature [6,7]. The room temperature structure of [(CH 3 ) 4 Z] 2 MX 4 where Z = As and/or P and M = Co 2+ or Zn +2 [8][9][10], consists of alternating layers of tetrahedral [(CH 3 ) 4 +2 and Pb +2 and X = Cl was synthesized [11][12].…”

“…Among these materials are compounds of the type [(CH 3 ) 4 X-ray diffraction studies showed that the tetramethylammonium salts [(CH 3 ) 4 N] 2 MX 4 , and tetramethylphosphonium salts, [(CH 3 ) 4 P] 2 MX 4 , are isostructural with the P121/c1 phase at room temperature [6,7]. The room temperature structure of [(CH 3 ) 4 Z] 2 MX 4 where Z = As and/or P and M = Co 2+ or Zn +2 [8][9][10], consists of alternating layers of tetrahedral [(CH 3 ) 4 +2 and Pb +2 and X = Cl was synthesized [11][12]. The electric properties of the Mn +2 and Cu +2 salts indicated the presence of structural phase transitions at 378 K and 411 K for the Cu +2 and at 368 K for the Mn +2 salts [11,12].…”