Melting of orientational degrees of freedom
We use calorimetry and dilatometry under hydrostatic pressure, X-ray powder diffraction and available literature data in a series of composition-related orientationally disordered (plastic) crystals to characterize both the plastic and melting transitions and investigate relationships between associ...
| Autores: | , , , |
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| Tipo de recurso: | artículo |
| Fecha de publicación: | 2017 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/105255 |
| Acceso en línea: | https://hdl.handle.net/2117/105255 https://dx.doi.org/10.1140/epjst/e2016-60315-4 |
| Access Level: | acceso abierto |
| Palabra clave: | Calorimetry X-rays -- Diffraction Plastics Calorimetria Raigs X -- Difracció Plàstics Àrees temàtiques de la UPC::Física |
| Sumario: | We use calorimetry and dilatometry under hydrostatic pressure, X-ray powder diffraction and available literature data in a series of composition-related orientationally disordered (plastic) crystals to characterize both the plastic and melting transitions and investigate relationships between associated thermodynamic properties. First, general common trends are identified: (i) The temperature range of stability of the plastic phase Tm-Tt (where Tt and Tm are the plastic and melting transition temperatures, respectively) increases with increasing pressure and (ii) both the rate of this increase, d(Tm-Tt)/dp, and the entropy change across the plastic transition analyzed as function of the ratio Tt/Tm are quite independent of the particular compound. However, the dependence of the entropy change at the melting transition on Tt/Tm at high pressures deviates from the behavior observed at normal pressure for these and other plastic crystals. Second, we find that the usual errors associated with the estimations of second-order contributions in the Clausius-Clapeyron equation are high and thus these terms can be disregarded in practice. Instead, we successfully test the validity of the Clausius-Clapeyron equation at high pressure from direct measurements. References |
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