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Related Concept Videos

Coordination Number and Geometry02:57

Coordination Number and Geometry

18.9K
For transition metal complexes, the coordination number determines the geometry around the central metal ion. Table 1 compares coordination numbers to molecular geometry. The most common structures of the complexes in coordination compounds are octahedral, tetrahedral, and square planar.
18.9K
Valence Bond Theory02:42

Valence Bond Theory

11.2K
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
11.2K
Crystal Field Theory - Tetrahedral and Square Planar Complexes02:46

Crystal Field Theory - Tetrahedral and Square Planar Complexes

48.1K
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,...
48.1K
Crystal Field Theory - Octahedral Complexes02:58

Crystal Field Theory - Octahedral Complexes

30.6K
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...
30.6K
Stereoisomerism02:52

Stereoisomerism

13.8K
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
13.8K
Metallic Solids02:37

Metallic Solids

20.5K
Metallic solids such as crystals of copper, aluminum, and iron are formed by metal atoms. The structure of metallic crystals is often described as a uniform distribution of atomic nuclei within a “sea” of delocalized electrons. The atoms within such a metallic solid are held together by a unique force known as metallic bonding that gives rise to many useful and varied bulk properties.
All metallic solids exhibit high thermal and electrical conductivity, metallic luster, and malleability....
20.5K

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Related Experiment Video

Updated: Jan 14, 2026

Synthesis of Programmable Main-chain Liquid-crystalline Elastomers Using a Two-stage Thiol-acrylate Reaction
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Synthesis of Programmable Main-chain Liquid-crystalline Elastomers Using a Two-stage Thiol-acrylate Reaction

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Locking Tetrahedral Ge Coordination Enables Stable Multilevel Phase-Change Memory.

Ruirui Liu1, Liu Liu1, Yukun Chen1

  • 1School of Materials Science and Engineering, Shanghai Institute of Technology, Shanghai 201418, China.

ACS Applied Materials & Interfaces
|January 13, 2026
PubMed
Summary
This summary is machine-generated.

Researchers developed a novel superlattice structure for phase-change random access memory (PCRAM). This design enhances storage density and reliability by stabilizing the memory state, paving the way for advanced nonvolatile memory solutions.

Keywords:
Ge buffered layermultilevel storagesequential crystallizationsuperlattice-like structuretetrahedral Ge coordination

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Area of Science:

  • Materials Science
  • Solid-State Physics
  • Nanotechnology

Background:

  • Phase-change random access memory (PCRAM) is a promising nonvolatile memory technology.
  • Current PCRAM faces challenges with storage density and resistance drift.
  • Superlattice structures offer potential for improved memory performance.

Purpose of the Study:

  • To engineer a superlattice structure for enhanced PCRAM.
  • To address limitations in storage density and resistance drift.
  • To enable reliable multilevel storage in next-generation memory devices.

Main Methods:

  • Fabrication of a [GeTe(24 nm)/Ge(2 nm)/Ge2Sb2Te5(24 nm)]1 superlattice.
  • Incorporation of an ultrathin Germanium (Ge) buffer layer.
  • Analysis of structural transitions and crystallization pathways.

Main Results:

  • The Ge buffer layer promotes tetrahedral Ge units, suppressing the "umbrella-flip" transition in Ge2Sb2Te5.
  • Structural stabilization of the intermediate-resistance state was achieved.
  • A well-defined crystallization pathway from amorphous to FCC to hexagonal (HEX) phases was observed.

Conclusions:

  • Ge-buffered superlattice structures offer a robust platform for high-density multilevel memory.
  • The engineered structure effectively suppresses resistance drift and enhances memory reliability.
  • This approach advances the development of next-generation nonvolatile memory technologies.