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Related Concept Videos

Colors and Magnetism03:02

Colors 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.
Valence Bond Theory02:42

Valence Bond Theory

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...
Trends in Lattice Energy: Ion Size and Charge02:54

Trends in Lattice Energy: Ion Size and Charge

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure of the strength of this attraction. The lattice energy (ΔHlattice) of an ionic compound is defined as the energy required to separate one mole of the solid into its component gaseous ions. For the ionic solid sodium chloride, the lattice energy is the enthalpy change of the process:
Crystal Field Theory - Octahedral Complexes02:58

Crystal 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...
Ionic Crystal Structures02:42

Ionic 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...
Lattice Energies of Ionic Crystals01:27

Lattice Energies of Ionic Crystals

Lattice energy represents the energy released when gaseous cations and anions combine to form an ionic solid, reflecting the strength of electrostatic interactions within the crystal. This process is fundamentally governed by Coulombic attraction between oppositely charged ions, where the potential energy varies inversely with the interionic distance and directly with the product of ionic charges. As ions approach one another, the electrostatic energy becomes increasingly negative, indicating a...

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Updated: Jul 5, 2026

Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides
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Published on: May 29, 2018

Anelasticity in MgAl2O4spinel due to cation order-disorder.

Simon Redfern1,2,3, Joanna Walsh4

  • 1Asian School of the Environment, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.

Journal of Physics. Condensed Matter : an Institute of Physics Journal
|July 3, 2026
PubMed
Summary

Researchers measured the dynamic shear modulus and anelastic properties of magnesium aluminum oxide spinel (MgAl2O4) at high temperatures. They identified a relaxation peak attributed to Mg-Al exchange, demonstrating cation-exchange anelasticity.

Keywords:
anelastic relaxationcation order–disorderinternal frictionmechanical spectroscopyseismic attenuationspinel

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Area of Science:

  • Geophysics
  • Materials Science
  • Solid State Physics

Background:

  • Magnesium aluminum oxide spinel (MgAl2O4) is a critical material in high-temperature applications.
  • Understanding its anelastic properties is key to predicting its behavior under stress.

Purpose of the Study:

  • To investigate the dynamic shear modulus and anelastic properties of MgAl2O4 spinel.
  • To characterize the relaxation mechanisms governing its mechanical behavior at high temperatures.

Main Methods:

  • Dynamic mechanical analysis using a forced torsion pendulum.
  • Measurements conducted between 600 K and 1400 K at frequencies of 0.01-10 Hz.

Main Results:

  • A Debye-like peak in internal friction (Q^-1) was observed around 1057 K at 1 Hz.
  • A significant modulus defect of approximately 4 GPa was measured.
  • The relaxation process was characterized by an activation energy of 331 kJ mol^-1 and showed a broader peak than ideal, indicating a distribution of local environments.

Conclusions:

  • The observed relaxation is attributed to stress-induced, vacancy-mediated Mg-Al exchange between tetrahedral and octahedral sites.
  • This study provides mechanical spectroscopic evidence of cation-exchange anelasticity in MgAl2O4.
  • Non-convergent order-disorder phenomena generate a distinct dynamical signature within the seismic frequency band.