[N(CH{sub 3}){sub 3}H]{sub 2}ZnCl{sub 4}: Ferroelectric properties and characterization of phase transitions by Raman spectroscopy
The X-ray powder diffraction pattern shows that at room temperature, [N(CH{sub 3}){sub 3}H]{sub 2}ZnCl{sub 4} is crystallized in the orthorhombic system with Pnma space group. The phase transitions at T{sub 1} = 255 K, T{sub 2} = 282 K, T{sub 3} = 302 K, T{sub 4} = 320 K, and T{sub 5} = 346 K have been confirmed by the differential scanning calorimetry. The electrical technique was measured in the 10{sup −1}–10{sup 7 }Hz frequency range and 233–363 K temperature intervals. The temperature dependence of the dielectric constant at different temperatures proved that this compound is ferroelectric below 282 K. Besides, [N(CH{sub 3}){sub 3 }H]{sub 2}ZnCl{sub 4} shows classical ferroelectric behaviour near curie temperature. In order to characterize the phase transitions, Raman spectra have been recorded in the temperature range of 233–383 K and the frequency range related to the internal and external vibrations of the cations and anions (90–4000 cm{sup −1}). The temperature dependence of the Raman line shifts ν and the half-width Δν detects all phase transitions and confirms their nature, especially at 282 K that corresponds to the ferroelectric-paraelectric phase transition.