Zero Thermal Expansion and Local Structure in K_xMn_xFe_{2- x}Mo₃O₁₂-Based Materials

Area of Science:

• Materials Science
• Solid State Chemistry
• Crystallography

Background:

• Zero thermal expansion (ZTE) materials are crucial for applications requiring dimensional stability across temperature fluctuations.
• Achieving ZTE in single-phase materials over broad temperature ranges presents a significant scientific challenge.

Purpose of the Study:

• To design and synthesize KxMnxFe2-xMo3O12 materials with tunable thermal expansion properties.
• To investigate the relationship between local crystal structure and thermal expansion behavior.
• To explore the potential of these materials for dual functionality, including low emissivity.

Main Methods:

• Synchrotron X-ray diffraction (XRD) for macroscopic structure analysis.
• Neutron pair distribution function (PDF) analysis for local structure determination.
• Density functional theory (DFT) calculations and Raman spectroscopy for mechanistic insights.

Main Results:

• KxMnxFe2-xMo3O12 (x=0.4-1.0) samples were synthesized by adjusting the (KMn)3+ doping ratio.
• The KMnFeMo3O12 sample achieved zero thermal expansion (ZTE) with a linear thermal expansion coefficient (αl) of 0.51 × 10-6 K-1 from 100-800 K.
• Local monoclinic distortion in K0.4Mn0.4Fe1.6Mo3O12 contrasts with the hexagonal local structure in KMnFeMo3O12, influencing thermal expansion.
• KMnFeMo3O12 demonstrated low emissivity in the 1-2.5 µm near-infrared band.

Conclusions:

• Local structural distortions play a critical role in controlling the thermal expansion behavior of KxMnxFe2-xMo3O12.
• The KMnFeMo3O12 material exhibits dual functionality: tunable zero thermal expansion and low near-infrared emissivity.
• This material holds significant potential for advanced engineering applications demanding thermal stability and specific radiative properties.