Video Experimental Relacionado
Updated: Jul 9, 2026
11:54
Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures
Published on: February 8, 2018
El efecto isotópico del oxígeno y las transiciones estructurales de fase en los superconductores basados en La2CuO4
Science (New York, N.Y.)
|December 7, 1990
Resumen
El efecto del isótopo de oxígeno en los superconductores de cuprato está fuertemente relacionado con las transiciones de fase estructurales. Esto sugiere que las contribuciones electrónicas a la inestabilidad de la red son clave para la superconductividad en estos materiales.
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:
- La temperatura de transición superconductora (Tc) en cupratos es sensible a la composición isotópica.
- El efecto del isótopo de oxígeno (alpha ((o)) proporciona información sobre el mecanismo de emparejamiento en los superconductores.
Objetivo del estudio:
- Investigar la dependencia de dopaje del efecto del isótopo de oxígeno en La2-xSrxCuO(4) y La2-xBaxCuO(4).
- Explorar la relación entre el efecto isotópico, las transiciones estructurales de fase y la superconductividad en estos materiales.
Principales métodos:
- Variación sistemática del dopaje de estroncio (Sr) y bario (Ba) (x) en La2-x(Sr,Ba) xCuO(4).
- Medición del efecto del isótopo de oxígeno (alfa ((o)) en la temperatura de transición superconductora.
- Difracción de rayos X de sincrotrón para analizar parámetros estructurales y transiciones de fase.
Principales resultados:
- Valores máximos de alfa (> 0.5) observados cerca de x = 0.12 en ambos compuestos dopados con Sr y Ba.
- Pequeño cambio en los parámetros de celosía u ortorrombicidad con el intercambio de isótopos en materiales de alto alfa.
- Correlación entre el comportamiento anómalo de alfa, las transiciones estructurales de fase (Abm a P42) /ncm) y los niveles de dopaje.
Conclusiones:
- La inusual dependencia de dopaje del efecto isotópico está relacionada con la proximidad a las transiciones estructurales de fase.
- Las distorsiones estructurales estáticas no causan los grandes efectos de isótopos observados.
- Se implica una contribución electrónica a la inestabilidad de la red, con un pico de ~ 1/8 de agujero por átomo de Cu.
- Existe una fuerte conexión entre el dopaje de agujeros, las inestabilidades de inclinación del octaedro CuO6 y la superconductividad en los sistemas basados en La2CuO4.
Videos de Conceptos Relacionados
03:06Alkali Metals
Group 1 elements are soft and shiny metallic solids. They are malleable, ductile, and good conductors of heat and electricity. The melting points of the alkali metals are unusually low for metals and decrease going down the group, while the density increases going down the group with the exception of potassium (Table 1).
Table 1: Properties of the alkali metals
Table 1: Properties of the alkali metals
02:42Ionic Crystal Structures
Ionic crystals consist of two or more different kinds of ions that usually have different sizes. The packing of these ions into a crystal structure is more complex than the packing of metal atoms that are the same size.
Most monatomic ions behave as charged spheres, and their attraction for ions of opposite charge is the same in every direction. Consequently, stable structures for ionic compounds result (1) when ions of one charge are surrounded by as many ions as possible of the opposite...
Most monatomic ions behave as charged spheres, and their attraction for ions of opposite charge is the same in every direction. Consequently, stable structures for ionic compounds result (1) when ions of one charge are surrounded by as many ions as possible of the opposite...
02:58Crystal Field Theory - Octahedral Complexes
Crystal Field Theory
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
03:02Colors and Magnetism
Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
01:26Imperfections in Crystal Structure: Stoichiometric Point Defects
Schottky defects arise when some lattice points in a crystal, such as those in NaCl, remain unoccupied, creating lattice vacancies without disturbing the overall electrical neutrality of the crystal. This defect is common in ionic crystals where the positive and negative ions are similar in size, as seen in sodium chloride and cesium chloride. The presence of Schottky defects enables the crystal to conduct electricity to a small extent through an ionic mechanism. Electric fields cause nearby...
01:29Imperfections in Crystal Structure: Non-Stoichiometric Defects
Non-stoichiometric defects refer to a type of defect in the crystal structure of a compound where the ratio of its constituent elements deviates from the ideal stoichiometric ratio. There are two main types of non-stoichiometric defects: metal excess defects and metal deficiency defects.Metal excess defects occur when there is a slight surplus of metal ions than what is required by the stoichiometric ratio of the compound. For example, heating a sodium chloride crystal in sodium vapor results...