Distribution of cations and phase transition in ferrite Cu_0.5Fe_2.5O₄

Abstract

The measurements of the temperature dependence of electrical resistivity, Seebeck coefficient, and the saturation magnetization were performed on polycrystals Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+γ</inf> With all samples the anomalous behavior above 400°C was observed which manifested itself by a sudden increase of electrical resistivity, by the change from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n-</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-</tex> type of electrical conductivity, and by the irreversible course of the magnetization. Contrary to physical properties, the chemical analysis revealed no significant changes in the composition of ferrites during the transformation. Taking into account the electrical, magnetic, and X-ray investigation it was concluded that in quenched samples (Cu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1+</sup> + Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ) and Cu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> + Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ) pairs are more stable in the tetrahedral and the octahedral sites of the spinel lattice, respectively. After the transformation only Cu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1+</sup> and Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> are present in the ferrites which initiates their decomposition into haematite and delafossite.