Inestabilidades de valencia, transiciones de fase y abrupta expansión de la red a 5 K en el sistema YbGaGe
Serena Margadonna1, Kosmas Prassides, Andrew N Fitch
1Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, UK. sm413@cam.ac.uk
Journal of the American Chemical Society
|April 9, 2004
Resumen
La valencia mixta YbGa1.05Ge0.95 exhibe expansión térmica negativa debido a una abrupta transición de valencia Yb a 5 K. Las altas temperaturas conducen a trastornos estructurales y eventual colapso.
Área de la Ciencia:
- Ciencia de los materiales Ciencia de los materiales.
- Física de la materia condensada Física de la materia condensada
- Química del estado sólido.
Sus antecedentes:
- Los compuestos de valencia mixta muestran complejas propiedades electrónicas y estructurales.
- Los materiales en capas ofrecen características únicas de expansión térmica.
- Los compuestos basados en Yterbio (Yb) son conocidos por sus fluctuaciones de valencia.
Objetivo del estudio:
- Investigar la expansión térmica de YbGa1.05Ge0.95 desde 3-1123 K. Investigar la expansión térmica de YbGa1.05Ge0.95 desde 3-1123 K.
- Caracteriza las transiciones de fase y los cambios estructurales con la temperatura.
- Comprender el papel del estado de valencia Yb en el comportamiento de los materiales.
Principales métodos:
- Se empleó la difracción de rayos X sincrotrón en polvo.
- Las mediciones dependientes de la temperatura se llevaron a cabo en un amplio rango (3-1123 K).
Principales resultados:
- Se observó una abrupta transición de fase isosímetrica con expansión térmica negativa a 5 K.
- Esta transición es impulsada por un desplazamiento de valencia Yb de +(2 + epsilon) hacia +2.2.
- A 1123 K, la estructura se transforma en un tipo AlB2 con planos isovalentes Yb y Ga/Ge desordenados.
Conclusiones:
- El estado de valencia de Yb influye significativamente en la expansión térmica de YbGa1.05Ge0.95.
- El material exhibe un comportamiento único de expansión térmica negativa a bajas temperaturas.
- Se observa inestabilidad estructural a altas temperaturas y eventual colapso.
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