A thermodynamic explanation of the Invar effect

Lohaus, Stefan Haegeli; Heine, Matthew; Guzmán, Pedro E. Encinosa; Bernal-Choban, C. M.; Saunders, Claire; Shen, Guoyin; Hellman, Olle; Broido, David; Fultz, B.

doi:10.1038/s41567-023-02142-z

Cited by 17 publications

(3 citation statements)

References 47 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…While there have been many theories that aim to describe NTE mechanisms in various materials, they are mostly phenomenological and focused on interpreting experimental observations [2][3][4][5][6][7][8][9] . Nevertheless, a fundamental understanding and a predictive theory without experimental inputs applicable to all materials are still lacking.…”

Section: Introductionmentioning

confidence: 99%

Zentropy theory for accurate prediction of free energy, volume, and thermal expansion without fitting parameters

Liu,

Hew,

Shang

2024

Microstructures

View full text Add to dashboard Cite

Based on statistical mechanics, a macroscopically homogeneous system, i.e., a single phase in the present context, is composed of many independent configurations that the system embraces. The macroscopical properties of the system are determined by the properties and statistical probabilities of those configurations with respect to external conditions. The volume of a single phase is thus the weighted sum of the volumes of all configurations. Consequently, the derivative of the volume to temperature of a single phase depends on both the derivatives of the volumes of every configuration to temperature and the derivatives of their statistical probabilities to temperature, with the latter introducing nonlinear emergent behaviors. It is shown that the derivative of the volume to the temperature of the single phase can be negative, i.e., negative thermal expansion, due to the symmetry-breaking non-ground-state configurations with smaller volumes than that of the ground-state configuration and the rapid increase of the statistical probabilities of the former, and negative thermal expansion can be predicted without fitting parameters from the zentropy theory that combines quantum mechanics and statistical mechanics with the free energy of each configuration predicted from quantum mechanics and the partition function of each configuration calculated from its free energy.

show abstract

Section: Introductionmentioning

confidence: 99%

Zentropy theory for accurate prediction of free energy, volume, and thermal expansion without fitting parameters

Liu,

Hew,

Shang

2024

Microstructures

View full text Add to dashboard Cite

show abstract

“…Zero thermal expansion (ZTE) in alloys, is generally manipulated by rigorous spin-lattice-orbital coupling 1 – 4 , emerging in a variety of intermetallic compounds 5 – 9 , etc. Such compounds tend to be brittle because of their multiple covalent or ionic bonds and the lack of independent slip systems 10 – 12 .…”

Section: Introductionmentioning

confidence: 99%

An isotropic zero thermal expansion alloy with super-high toughness

Yu,

Lin,

Zhang

et al. 2024

Nat Commun

View full text Add to dashboard Cite

Zero thermal expansion (ZTE) alloys with high mechanical response are crucial for their practical usage. Yet, unifying the ZTE behavior and mechanical response in one material is a grand obstacle, especially in multicomponent ZTE alloys. Herein, we report a near isotropic zero thermal expansion (αl = 1.10 × 10−6 K−1, 260–310 K) in the natural heterogeneous LaFe54Co3.5Si3.35 alloy, which exhibits a super-high toughness of 277.8 ± 14.7 J cm−3. Chemical partition, in the dual-phase structure, assumes the role of not only modulating thermal expansion through magnetic interaction but also enhancing mechanical properties via interface bonding. The comprehensive analysis reveals that the hierarchically synergistic enhancement among lattice, phase interface, and heterogeneous structure is significant for strong toughness. Our findings pave the way to tailor thermal expansion and obtain prominent mechanical properties in multicomponent alloys, which is essential to ultra-stable functional materials.

show abstract

“…This implies that there is no anomaly in the lattice (phonon) part of the thermal expansion, but rather, there is an additional contribution related to the magnetic order. Very important recent experiments have provided clear evidence that the lattice and magnetic contributions to thermal expansion in INVAR alloy can be separated. The value of ω s at zero temperature, denoted as ω s0 = ω s (0), is a key experimental characteristic of Invar-type materials. , Therefore, the primary objective of the theory of the Invar effect is to predict and explain its anomalously high value.…”

Section: Introductionmentioning

confidence: 99%

Predictive Theory of Anomalous Volume Magnetostriction in Fe–Ni Alloys: Bond Repopulation Mechanism of the Invar Effect

Khmelevskyi,

Steiner

2023

J. Phys. Chem. C

View full text Add to dashboard Cite

We demonstrate that a quantitative description of the observed magnetovolume anomaly in Fe−Ni Invar alloys can be achieved by taking into account thermally induced longitudinal spin fluctuations on a first-principles basis. The experimental dependence of spontaneous volume magnetostriction on the Ni atomic concentration is readily reproduced. Our calculations predict the Invar anomaly in the Fe 65 Ni 35 INVAR alloy and its gradual vanishing for compositions with more than 50 at. % of Ni. The mechanism of the anomaly is linked to the repopulation of the electronic states in the majority and minority spin bands, accompanied by changes in their bonding character as thermal magnetic disorder increases in the system. These changes can be visualized using first-principles bond population analyses. It provides a simple, chemically intuitive picture of the mechanism of the Invar effect.

show abstract

A thermodynamic explanation of the Invar effect

Cited by 17 publications

References 47 publications

Zentropy theory for accurate prediction of free energy, volume, and thermal expansion without fitting parameters

Zentropy theory for accurate prediction of free energy, volume, and thermal expansion without fitting parameters

An isotropic zero thermal expansion alloy with super-high toughness

Predictive Theory of Anomalous Volume Magnetostriction in Fe–Ni Alloys: Bond Repopulation Mechanism of the Invar Effect

Contact Info

Product

Resources

About