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Related Concept Videos

Determination of Crystal Structures01:29

Determination of Crystal Structures

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In the late 1800s, the revelation that light extended beyond visible wavelengths led to the discovery of X-rays by Wilhelm Roentgen. Recognized as high-energy electromagnetic radiation with short wavelengths, X-rays prompted exploration into their interaction with crystals. Max von Laue proposed in 1912 that the periodic arrangement of atoms, ions, or molecules in crystals would cause them to diffract X-rays, a hypothesis confirmed through experiments with copper sulfate and zinc sulfide...
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Imperfections in Crystal Structure: Stoichiometric Point Defects01:26

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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...
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Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
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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...
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Imperfections in Crystal Structure: Point, Line and Plane Defects01:25

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A perfect crystal, in theory, has a uniform structure with the same unit cell and lattice points throughout. However, any deviation from this periodic arrangement is known as an imperfection or defect. These defects can be categorized into three types: point, line, and plane defects.Point defects occur when there is a deviation from the ideal due to missing atoms, displaced atoms, or additional atoms. These imperfections might occur due to imperfect packing during crystallization or because of...
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Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon
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Evolution of crystal structures in GeTe during phase transition.

Kwangsik Jeong1, Seungjong Park1, Dambi Park1

  • 1Institute of Physics and Applied Physics, Yonsei University, Seoul, 120-749, Republic of Korea.

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|April 21, 2017
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Summary

Researchers explored germanium telluride (GeTe) crystal structure changes during phase transitions. New P1 and Cm structures were identified, revealing coexistence and transformations that alter electrical resistance.

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Area of Science:

  • Materials Science
  • Solid-State Physics
  • Crystallography

Background:

  • Germanium telluride (GeTe) is a phase-change material with potential applications in memory and thermoelectric devices.
  • Understanding its structural transformations is crucial for optimizing device performance.

Purpose of the Study:

  • To investigate the crystal structure changes in GeTe during phase transitions.
  • To identify and characterize new crystalline phases of GeTe.
  • To correlate structural changes with alterations in electrical properties.

Main Methods:

  • Density Functional Theory (DFT) calculations were employed to predict possible crystal structures.
  • X-ray diffraction (XRD) and Raman spectroscopy were used to analyze GeTe films.
  • Internal energy calculations determined the stability and coexistence of different phases.

Main Results:

  • Four possible GeTe crystal structures (R3m, P1, Cm, Fm3m) were identified; P1 and Cm were newly examined.
  • DFT calculations and experimental XRD confirmed the coexistence of P1, R3m, and Cm phases.
  • Laser irradiation induced a transformation of the Cm phase into P1 or R3m.
  • Raman spectra supported the coexistence of multiple structures.
  • Calculated band gaps indicated that structural transformations alter GeTe's electrical resistance.

Conclusions:

  • The study reveals the coexistence and interconversion of multiple crystal structures in GeTe.
  • These structural dynamics contribute to the facile phase change and instability observed in GeTe.
  • The findings provide insights into the mechanisms governing GeTe phase transitions and their impact on electronic properties.