[N(CH3)3H]2ZnCl4: Ferroelectric properties and characterization of phase transitions by Raman spectroscopy

The X-ray powder diffraction pattern shows that at room temperature, [N(CH₃)₃H]₂ZnCl₄ is crystallized in the orthorhombic system with Pnma space group. The phase transitions at T₁ = 255 K, T₂ = 282 K, T₃ = 302 K, T₄ = 320 K, and T₅ = 346 K have been confirmed by the differential scanning calorimetry. The electrical technique was measured in the 10^-1-10⁷ 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(CH₃)₃H]₂ZnCl₄ 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^-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.