Analysis of the suppression of the ferroelectric-paraeletric transition and its Curie's temperature in a doped host-structure niobate

Fe-doped potassium-strontium niobate solid solution with centrosymmetric space group was engineered from ferroelectric KSr₂Nb₅O₁₅ host-structure, a classical structure with non-centrosymmetric space-group. A single-phase and crystalline solid solution was prepared via solid state reaction after mechanical mixture of oxides via High Energy Ball Milling. Structural properties of this non-stoichiometric solid solution were investigated by X-ray Diffraction, Raman spectroscopy, X-ray Absorption spectroscopy and Mössbauer spectroscopy. The analyses showed non-isovalent Fe³⁺ cations bi-site substitution on the Nb⁵⁺ cations octahedral sites. The development of a non-ferroelectric state (centrosymmetric) was observed from niobium substitution by Fe³⁺, suppressing ferroelectric-paraelectric phase transition. Further, the absence of Curie's temperature with a non-ferroelectric state was characterized by high-temperature Dielectric spectroscopy, from room temperature up to 965 K. Non-stoichiometric KSr₂(FeNb₄)O_15-δ exhibited semiconductor character with negative temperature coefficient. Centrosymmetric space group and covalent character niobium oxygen bond stemming induction of non-polar ferroelectric configuration are discussed.