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Polimorfismo en NaSbO3: estructura y unión en óxidos metálicos
Hiroshi Mizoguchi1, Patrick M Woodward, Song-Ho Byeon
1Department of Chemistry, Ohio State University, Columbus, Ohio 43210-1185, USA.
Journal of the American Chemical Society
|March 12, 2004
Resumen
Un nuevo antimonato de sodio (NaSbO(3)) polimórfico con una estructura de perovskita fue sintetizado bajo alta presión. Este descubrimiento arroja luz sobre los complejos enlaces y preferencias estructurales en los compuestos antimonatos ternales.
Área de la Ciencia:
- Química del estado sólido.
- Ciencia de los materiales ciencia de los materiales.
- La cristalografía es una técnica de cristalografía.
Sus antecedentes:
- Las perovskitas ternales son cruciales en la ciencia de los materiales, pero su diversidad estructural y su estabilidad bajo presión no se comprenden completamente.
- Se sabe que el antimonato de sodio (NaSbO(3)) existe en un polimorfo de ilmenita bajo condiciones ambientales.
Objetivo del estudio:
- Para sintetizar y caracterizar un nuevo polimorfo de alta presión de NaSbO.
- Investigar las propiedades estructurales, electrónicas y de unión de este nuevo material.
- Comprender los factores que rigen la estabilidad de diferentes polimorfas de NaSbO.
Principales métodos:
- Síntesis de alta presión utilizando una prensa tipo yunque de esfera dividida uniaxial (USSA-2000) a 10.5 GPa y 1150 grados C.
- Difracción de rayos X para la determinación de la estructura cristalina.
- Mediciones ópticas para determinar el espacio entre las bandas.
Principales resultados:
- Se sintetizó con éxito un nuevo polimorfo perovskita distorsionado ortorrómbico de NaSbO(3) y se recuperó a las condiciones ambientales.
- La estructura (grupo espacial Pnma) exhibe una significativa distorsión de inclinación octaédrica, mayor de lo previsto por los radios iónicos.
- El compuesto es un aislante blanco con una brecha de banda óptica de 3.4 eV, que representa la primera perovskita ternaria con Sb ((5+) en el sitio octaédrico.
Conclusiones:
- La distorsión observada se atribuye a un efecto Jahn-Teller de segundo orden sobre el oxígeno, impulsado por un fuerte enlace covalente Sb-O.
- Un conflicto entre la unión covalente Sb-O y las interacciones repulsivas Na-O desestabiliza la estructura de la perovskita en condiciones ambientales, favoreciendo el polimorfo ilmenita.
- El análisis de la unión explica la prevalencia de estructuras que violan las reglas de Pauling en los compuestos ASbO ((3) y ABiO ((3).
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