Structural Investigation and Electrical Properties on K₂Mg_(1−x)Zn_x(SO₄)₂·6H₂O: A Selective Picromerite-Type Electrode Materials

A series of K₂Mg_(1−x)Zn_x(SO₄)₂.6H₂O (x = 0, 0.6, 1) materials have been prepared by slow evaporation method at room temperature. Characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) reveal the presence of pure single monoclinic phases (space group P2₁/a, Z = 2). Refined parameters shows that the substitution of Mg²⁺ by Zn²⁺ increases unit cell dimensions of picromerite-type phase. The vibrational characteristic of \({\text{SO}}_{4}^{2 - }\) ${\text{SO}}_4^{2-}$ groups and water molecules have been identified in the 400–4000 cm⁻¹ wavenumber region. The results of electrical conductivity determined by impedance spectroscopy in the [633–693 K] temperature range for sintered pellets showed a maximum total conductivity of 3.65 × 10^–6 S cm⁻¹ and a minimum activation energy of 0.54 eV were obtained at 673 K for K₂Mg(SO₄)₂ sample. The ac-conductivity (σ_ac) measurements exhibit features typical characteristics of the universal dynamic response. The obtained results suggested that these materials are suitable candidates for application as electrodes in potassium-ion batteries (PIBs).