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La transición de valencia inducida por la temperatura y el colapso de la red asociado en el fulleruro de samario
J Arvanitidis1, Konstantinos Papagelis, Serena Margadonna
1Department of Chemistry, University of Sussex, Brighton BN1 9QJ, UK.
Nature
|October 10, 2003
Resumen
Las fulleridas de tierras raras exhiben propiedades únicas debido a los sistemas de electrones acoplados. El enfriamiento Sm2.75C60 induce una transición de fase con una expansión térmica negativa significativa, vinculada a un cambio de valencia de samario.
Área de la Ciencia:
- Física de la materia condensada Física de la materia condensada
- Ciencia de los materiales Ciencia de los materiales.
- Química Química es la química.
Sus antecedentes:
- Los sistemas de electrones fuertemente correlacionados muestran propiedades físicas inusuales.
- Las fuleridas de tierras raras, con tierras raras acopladas y subratos C60, son materiales intrigantes.
- Estos sistemas son difíciles de modelar teóricamente.
Objetivo del estudio:
- Investigar las propiedades físicas de las fulleridas de tierras raras.
- Caracteriza la transición de fase en Sm2.75C60.
- Comprender el mecanismo detrás de la expansión térmica negativa en estos materiales.
Principales métodos:
- Difracción de rayos X sincrotrón de alta resolución.
- Mediciones de la susceptibilidad magnética.
- Análisis de la expansión térmica.
Principales resultados:
- Se observó una transición de fase isosímetrica en Sm2.75C60 cerca de 32 K.
- Esta transición implicó un dramático aumento de volumen isotrópico y un cambio de valencia de samario.
- Se observó una expansión térmica negativa sin precedentes, 40 veces mayor que en los óxidos metálicos típicos.
Conclusiones:
- La expansión térmica negativa observada se atribuye a una transición de valencia casi continua del samario.
- Este comportamiento es análogo a las transiciones de valencia en aislantes Kondo de valencia intermedia.
- Las fuleridas de tierras raras ofrecen una plataforma novedosa para estudiar fenómenos de electrones fuertemente correlacionados.
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