Oxygen order-disorder phase transition in layered GdBaCo2O 5+δ perovskite: Thermodynamic and transport properties
The effects of the orthorhombic (O) to tetragonal (T) phase transition around 450/500 C on the thermodynamic and transport properties of the layered cobaltite GdBaCo2O5+δ have been investigated in detail using complementary techniques such as thermo-gravimetry (TG), differential scanning calorimetry...
| Autores: | , , , |
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| Formato: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2013 |
| País: | Argentina |
| Recursos: | Consejo Nacional de Investigaciones Científicas y Técnicas |
| Repositorio: | CONICET Digital (CONICET) |
| Idioma: | inglés |
| OAI Identifier: | oai:ri.conicet.gov.ar:11336/2067 |
| Acesso em linha: | http://hdl.handle.net/11336/2067 |
| Access Level: | acceso abierto |
| Palavra-chave: | ELECTRON-HOLE TRANSPORT GDBACO2O5+Δ LAYERED PEROVSKITES ORDER-DISORDER PHASE TRANSITION THERMODYNAMIC PROPERTIES https://purl.org/becyt/ford/1.3 https://purl.org/becyt/ford/1 https://purl.org/becyt/ford/1.4 |
| Resumo: | The effects of the orthorhombic (O) to tetragonal (T) phase transition around 450/500 C on the thermodynamic and transport properties of the layered cobaltite GdBaCo2O5+δ have been investigated in detail using complementary techniques such as thermo-gravimetry (TG), differential scanning calorimetry (DSC), dilatometry, angle dispersive as well as energy dispersive high temperature X-ray diffraction (HT-XRD and ED-XRD). Experimental data show that the O/T transition temperature shifts to higher values when the pO2 of the experiment increases. The equilibrium pO2 data shows the presence of a narrow two-phase field around 5 + δ ≈ 5.42. The presence of a two-phase field together with an enthalpy change (â̂†H ≈ 4 J/g) and HT-XRD data showing coexistence of both phases confirms that this phase transition is first-order type. Oxygen partial molar enthalpy and entropy of both phases, the "ordered" O and the "disordered" T, are obtained from TG under controlled pO 2, and yield lower entropy and enthalpy values for the ordered O phase. The O/T phase transition at constant temperature involves a volume contraction and a density change of 0.3%. Isotherms of electrical conductivity as a function of pO2 show that this compound exhibits itinerant charge carrier behavior regardless of the crystal symmetry. The charge carrier mobility decreases for the T phase, which might be due to the shortening of CoOCo distance along a-direction. |
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