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DOE OSTI · 1885314

Understanding the Re-entrant Phase Transition in a Non-magnetic Scheelite

Saura-Múzquiz, Matilde·Marlton, Frederick P.·Mullens, Bryce G.·Manjón-Sanz, Alicia María·Neuefeind, Joerg C.·Everett, Michelle·Brand, Helen A.·Mondal, Subrata·Vaitheeswaran, Ganapathy·Kennedy, Brendan J.
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Abstract

We report the stereochemical activity of lone pair electrons plays a central role in determining the structural and electronic properties of both chemically simple materials such as H 2 O, as well as more complex condensed phases such as photocatalysts or thermoelectrics. TlReO 4 is a rare example of a non-magnetic material exhibiting a re-entrant phase transition and emphanitic behavior in the long-range structure. Here, we describe the role of the Tl + 6s 2 lone pair electrons in these unusual phase transitions and illustrate its tunability by chemical doping, which has broad implications for functional materials containing lone pair bearing cations. First-principles density functional calculations clearly show the contribution of the Tl + 6s 2 in the valence band region. Local structure analysis, via neutron total scattering, revealed that changes in the long-range structure of TlReO 4 occur due to changes in the correlation length of the Tl + lone pairs. This has a significant effect on the anion interactions, with long-range ordered lone pairs creating a more densely packed structure. This resulted in a trade-off between anionic repulsions and lone pair correlations that lead to symmetry lowering upon heating in the long-range structure, whereby lattice expansion was necessary for the Tl + lone pairs to become highly correlated. Similarly, introducing lattice expansion through chemical pressure allowed long-range lone pair correlations to occur over a wider temperature range, demonstrating a method for tuning the energy landscape of lone pair containing functional materials.

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRYPDFScheelitecation orderdisorderlone pairphase transition

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Saura-Múzquiz, Matilde, Marlton, Frederick P., Mullens, Bryce G., Manjón-Sanz, Alicia María, Neuefeind, Joerg C., Everett, Michelle, Brand, Helen A., Mondal, Subrata, Vaitheeswaran, Ganapathy, Kennedy, Brendan J.. 2022-08-22. Understanding the Re-entrant Phase Transition in a Non-magnetic Scheelite. https://doi.org/10.1021/jacs.2c05620

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