Thermal expansion in harmonic potential

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SUMMARY

Thermal expansion in crystalline solids is primarily influenced by anharmonic terms in the potential; however, Landau and Lifshitz's "Course of Theoretical Physics," specifically in Statistical Physics part 1, paragraph 67, presents a derivation of the thermal expansion coefficient from the free energy of a harmonic solid. This raises questions about the presence of thermal expansion in a purely harmonic potential. Ashby’s insights indicate that atomic bonds demonstrate linear elasticity only for small displacements, suggesting that the derived expansion coefficient is valid within this limited range.

PREREQUISITES
  • Understanding of harmonic and anharmonic potentials in solid-state physics
  • Familiarity with the concepts of thermal expansion and elasticity
  • Knowledge of statistical mechanics, particularly free energy calculations
  • Basic principles of crystallography and atomic bonding
NEXT STEPS
  • Study the derivation of thermal expansion coefficients in Landau and Lifshitz's "Course of Theoretical Physics"
  • Explore the implications of anharmonicity in solid-state physics
  • Research linear elasticity and its limitations in atomic bonding
  • Investigate the role of temperature in the behavior of crystalline solids
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Physicists, materials scientists, and students studying solid-state physics, particularly those interested in the relationship between thermal properties and atomic structure in crystalline materials.

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It is generally said that thermal expansion is a process determinated by the anharmonic terms in the potential of a crystalline solid. However, in the Course of Theoretical Physics by Landau Lifshitz, Statistical Physics part 1, paragraph 67, a form for the coefficient of thermal expansion is derived from the free energy of a harmonic solid. How's that possible if in an harmonic potential no thermal expansion should be present? Thanks in advance!
 
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Ashby suggests that the atomic bond exhibits linear elasticity for only small relative displacement of atoms. I presume that this is the range for which the expansion coefficient is valid.
 

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