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Expansión térmica negativa mejorada inducida por transferencia de carga simultánea y transiciones polares-no polares
Takumi Nishikubo1, Yuki Sakai1,2, Kengo Oka3
1Laboratory for Materials and Structures , Tokyo Institute of Technology , 4259 Nagatsuta, Midori-ku , Yokohama , Kanagawa 226-8503 , Japan.
Journal of the American Chemical Society
|November 19, 2019
Resumen
Se observó una expansión térmica negativa en el óxido de hierro de níquel bismuto debido a la transferencia de carga y las transiciones de fase. Este nuevo hallazgo en BiNi1-xFexO3 ofrece nuevas posibilidades de materiales.
Área de la Ciencia:
- Ciencias de los materiales
- Química del estado sólido
- La cristalografía
Sus antecedentes:
- La expansión térmica negativa (NTE) es una propiedad en la que los materiales se contraen al calentarse.
- Comprender los mecanismos detrás de NTE es crucial para el desarrollo de materiales funcionales avanzados.
- Los óxidos a base de bismuto son conocidos por sus diversas propiedades estructurales y electrónicas.
Objetivo del estudio:
- Investigar la ocurrencia y los mecanismos de expansión térmica negativa en BiNi1-xFexO3.
- Explorar la relación entre composición, estructura y propiedades de expansión térmica.
- Identificar los mecanismos simultáneos que impulsan el NTE en este sistema de materiales.
Principales métodos:
- Síntesis de compuestos de BiNi1-xFexO3 con contenido de hierro variable (0,25 ≤ x ≤ 0,5).
- Difracción de rayos X (XRD) y análisis estructural dependiente de la temperatura para determinar la estructura cristalina y las transiciones de fase.
- Análisis de la distribución de la carga y los estados electrónicos.
Principales resultados:
- Primera observación de NTE en BiNi1-xFexO3 (0.25 ≤ x ≤ 0.5) impulsado por la transferencia de carga simultánea y las transiciones polar-no polar.
- Identificación de una fase polar de baja temperatura (grupo espacial R3c) con una distribución de carga específica (Bi3+/Bi5+/Ni2+/Fe3+).
- La reducción de volumen al calentarse disminuyó con el aumento de x debido a la reducción de Ni2+, mientras que una reducción de volumen independiente de la composición de ~2% se relacionó con las transiciones polar-no polares.
Conclusiones:
- La transferencia simultánea de carga (Bi5+-Ni2+) y las transiciones polares-no polares son los mecanismos clave para el NTE en BiNi1-xFexO3.
- El alcance de la NTE de la transferencia de carga depende de la composición, mientras que la contribución de las transiciones de fase es independiente de la composición.
- Este estudio revela una nueva vía para diseñar materiales con propiedades de expansión térmica negativa a medida.
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