Issue 32, 2020

The impact of morphotropy and polymorphism on electric properties of manganites: the case of Sr0.5Ca0.5Mn1−xVxO3−δ

Abstract

The electron conductors Sr0.5Ca0.5Mn1−xVxO3−δ (x = 0.025, 0.05, and 0.1) synthesized via the citrate–nitrate route have been characterized by powder X-ray diffraction at room temperature and at high temperatures in air. At room temperature, the symmetry of unit cells of corresponding morphotropes change from orthorhombic (space group Pbnm) to tetragonal (space group I4/mcm) due to the cooperative Jahn–Teller effect. In samples with x = 0.05 and x = 0.10, the temperature of phase transition from the orthorhombic (space group Pbnm) to tetragonal (space group I4/mcm) polymorph is found to decrease with the increasing vanadium content. The phase transition from tetragonal to cubic (I4/mcmPm[3 with combining macron]m) in all samples occur around 673 K. The electrical conductivity (σ) and Seebeck coefficient (S) have been measured in air within 330–1220 K. The increase in absolute values of S with rising temperature is explained employing the model of motion of small polarons, considering the disproportionation of Mn3+ ions to Mn2+ and Mn4+ and the spin direction of t2g-electrons of manganese. The obtained data allow the calculation for the concentration and mobility of charge carriers. The decrease in enthalpy of disproportionation reaction and mobility activation energy is associated with the declining trend of Jahn–Teller distortions following polymorphic transitions with increasing temperature or morphotropic transitions I4/mcmPbnm at low temperatures.

Graphical abstract: The impact of morphotropy and polymorphism on electric properties of manganites: the case of Sr0.5Ca0.5Mn1−xVxO3−δ

Article information

Article type
Paper
Submitted
05 Apr 2020
Accepted
14 Jul 2020
First published
15 Jul 2020

J. Mater. Chem. A, 2020,8, 16497-16505

The impact of morphotropy and polymorphism on electric properties of manganites: the case of Sr0.5Ca0.5Mn1−xVxO3−δ

E. I. Konstantinova, I. A. Leonidov, A. A. Markov, R. F. Samigullina, A. V. Chukin and I. I. Leonidov, J. Mater. Chem. A, 2020, 8, 16497 DOI: 10.1039/D0TA03731A

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