Localized Symmetry Breaking for Tuning Thermal Expansion in ScF₃ Nanoscale Frameworks

Abstract

The local symmetry, beyond the averaged crystallographic structure, tends to bring unusual performances. Negative thermal expansion is a peculiar physical property of solids. Here, we report the delicate design of the localized symmetry breaking to achieve controllable thermal expansion in ScF nanoscale frameworks. Intriguingly, an isotropic zero thermal expansion is concurrently engineered by localized symmetry breaking, with a remarkably low coefficient of thermal expansion of about +4.0 × 10/K up to 675 K. This mechanism is investigated by the joint analysis of atomic pair distribution function of synchrotron X-ray total scattering and extended X-ray absorption fine structure spectra. A localized rhombohedral distortion presumably plays a critical role in stiffening ScF nanoscale frameworks and concomitantly suppressing transverse thermal vibrations of fluorine atoms. This physical scenario is also theoretically corroborated by the extinction of phonon modes with negative Grüneisen parameters in rhombohedral ScF. The present work opens an untraditional chemical modification route to achieve controllable thermal expansion by breaking local symmetries in materials.

High Thermoelectric Performance through Crystal Symmetry Enhancement in Triply Doped Diamondoid Compound Cu2SnSe3

“…PDF is a powerful technique, which could be used to analyze local structures in functional materials. [ 34 ] The first peak in G( r ) function located around 2–3 Å is assigned to the nearest neighboring MSe bonds (M = Cu/Ag/Sn/Ga/Na), as shown by the green circle in Figure 6 a. In the cubic AgGaNa3, all MSe bond should be identical due to crystallographic symmetry constrain.…”

Perovskite-related ReO3-type structures

“…85 Furthermore, it was recently shown that the degree of NTE in ScF 3 is particle size dependent, 96 and can actually be tuned between NTE, zero thermal expansion (ZTE), and PTE, by nanostructuring the product. 97 The tunability has been ascribed to local symmetry breaking as the particle size is decreased, i.e. the local structure is rhombodrally distorted (as evi- Figure 4: Lattice constant versus temperature (log scale).…”

Quantitative understanding of negative thermal expansion in scandium trifluoride from neutron total scattering measurements

“…We collected total neutron scattering data from a powder sample of scandium trifluoride, measuring both the Bragg scattering-sensitive to the long-range order-and the diffuse scattering. Although several previous pair distribution function studies of ScF 3 have used x-rays [15,[27][28][29], for our analysis neutron radiation was a more appropriate choice, for three reasons. First, the accessible range of scattering vector Q, and hence the resolution of the pair distribution function derived from it, is much greater: we were able to measure up to a maximum value of Q max = 50 Å −1 , while with x rays the maximum achievable value of Q with a short-wavelength silver anode is 22.5 Å −1 and is usually practically up to around 30 Å −1 with synchrotron radiation measurements.…”