Conventional strategies for suppressing lattice thermal conductivity κ _L typically focus on maximizing phonon scattering to reduce phonon mean free path. Such reductions, however, are limited to the interatomic spacing or phonon wavelength. Alternatively, herein, an effective approach is proposed to lower phonon velocity by introducing atoms with significant atomic mismatch into the crystal lattice of three meta‐phases. Specifically, substituting Te for S in Ag ₈ SnS ₆ and Cu ₂ S, or Sn for Si in Mg ₂ Si considerably increases the atomic mass and weakens the chemical bonding, causing notable reductions in the sound velocity. This reduction further leads to an amorphous‐like, extremely low lattice thermal conductivity κ _L across the whole temperature range. Consequently, we achieve outstanding thermoelectric performance in these atomic mismatched meta‐phases, with a maximum zT of 1.0 for Ag ₈ SnS _4.99 Te, 1.1 for Mg ₂ Si _0.5 Sn _0.5 , and 2.0 for Cu ₂ S _0.5 Te _0.5 . The work demonstrates a new approach to manipulating thermal conductions through lattice softening, providing a promising pathway for designing high‐performance thermoelectric materials.

Compared to X-rays, electrons have stronger interactions with matter. In electron diffraction, the low-order structure factors are sensitive to subtle changes in the arrangement of valence electrons around atoms when the scattering vector is smaller than the critical scattering vector. Therefore, electron diffraction is more advantageous for studying the distribution of atoms in the structure with atomic numbers smaller than that of sulfur. In this work, the crystal structure of Sr_1.2Ca_0.8Nb₂O₇ (SCNO-0.8) was analyzed using single-crystal X-ray diffraction (SC-XRD) and three-dimensional electron diffraction (3D-ED) techniques, respectively. Interestingly, the superstructure could only be identified by the 3D-ED technique, while no signal corresponding to the superstructure was detected from the SC-XRD data. The superstructure in SCNO-0.8 was disclosed to be caused by different tilting of NbO₆ octahedra and the displacements of Sr/Ca atoms in the different atomic layers perpendicular to the a-axis. Therefore, the application of 3D-ED provides an effective method for studying superstructures caused by ordered arrangements of light atoms.

As an important characterization method, pair distribution function (PDF) has been extensively used in structural analysis of nanomaterials, providing key insights into the degree of crystallinity, atomic structure, local disorder etc. The collection of scattering signals with good statistics is necessary for a reliable structural analysis. However, current conventional electron diffraction experiments using PDF (ePDF) are limited in their ability to acquire continuous diffraction rings for large nanoparticles. Herein, a new method – tilt-ePDF – is proposed to improve the data quality and compatibility of ePDF by a combination of electron diffraction and specimen tilting. In the present work, a tilt-series of electron diffraction patterns was collected from gold nanoparticles with three different sizes and a standard sample polycrystalline aluminium film for ePDF analysis. The results show that tilt-ePDF can not only enhance the continuity of diffraction rings, but can also improve the signal-to-noise ratio in the high scattering angle range. As a result, compared with conventional ePDF data, tilt-ePDF data provide structure parameters with a better accuracy and lower residual factors in the refinement against the crystal structure. This method provides a new way of utilizing ePDF to obtain accurate local structure information from nanoparticles.