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)O15-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.