The impact of morphotropy and polymorphism on electric properties of manganites: the case of Sr0.5Ca0.5Mn1−xVxO3−δ
| Autor: | Ilia A. Leonidov, Andrey V. Chukin, Ivan I. Leonidov, Alexey A. Markov, Rina F. Samigullina, E. I. Konstantinova |
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| Rok vydání: | 2020 |
| Předmět: |
Phase transition
Materials science Renewable Energy Sustainability and the Environment Enthalpy Analytical chemistry Disproportionation 02 engineering and technology General Chemistry Activation energy 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences 0104 chemical sciences Tetragonal crystal system Electrical resistivity and conductivity Seebeck coefficient General Materials Science Orthorhombic crystal system 0210 nano-technology |
| Zdroj: | Journal of Materials Chemistry A. 8:16497-16505 |
| ISSN: | 2050-7496 2050-7488 |
| DOI: | 10.1039/d0ta03731a |
| Popis: | 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/mcm ↔ Pmm) 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/mcm → Pbnm at low temperatures. |
| Databáze: | OpenAIRE |
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