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Sobre la transición de fase a alta temperatura de Gd5Si2Ge2
Yurij Mozharivskyj1, Alexandra O Pecharsky, Vitalij K Pecharsky
1Ames Laboratory, Materials and Engineering Physics Program, Iowa State University, Ames, Iowa 50011-3020, USA.
Journal of the American Chemical Society
|January 6, 2005
Resumen
La transición de fase en Gd(5) Si(2) Ge(2) se produce alrededor de 300-320°C. Las impurezas como el oxígeno y el nitrógeno afectan significativamente esta transición, contrariamente a las predicciones anteriores.
Área de la Ciencia:
- Ciencia de los materiales Ciencia de los materiales.
- Física del estado sólido Física del estado sólido
- La cristalografía es una técnica de cristalografía.
Sus antecedentes:
- Los compuestos basados en gadolinio como Gd(5) Si(2) Ge(2) son materiales magnetocalóricos gigantes clave.
- Comprender las transiciones de fase es crucial para optimizar las aplicaciones de refrigeración magnética.
Objetivo del estudio:
- Para investigar la transición de fase monoclínica a ortorrómbica (beta-->gamma) en Gd(5) Si(2) Ge(2).
- Examinar la influencia de las impurezas intersticiales en esta transición.
Principales métodos:
- Difracción de rayos X monocristalino de alta temperatura in situ. difracción de rayos X.
- Desarrollo de una técnica especializada de montaje de cristales para prevenir la contaminación.
Principales resultados:
- La transición beta->gamma ocurre de manera reversible entre 300-320°C al calentarse y enfriarse lentamente, pero irreversiblemente al enfriarse rápidamente.
- Contrariamente a las predicciones, la distribución de los átomos de Si y Ge sigue siendo consistente en todas las fases.
- Las impurezas, particularmente el oxígeno y el nitrógeno, alteran significativamente la temperatura de transición, completándola solo a 600 ° C en presencia de aire.
Conclusiones:
- Las impurezas intersticiales, alojadas en huecos entre las láminas, juegan un papel crítico en la estabilidad y el comportamiento de transición de Gd(5) Si(2) Ge(2).
- El estudio desafía los modelos teóricos anteriores con respecto a la distribución atómica y los efectos de las impurezas.
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