Isotropic negative thermal expansion and its mechanism in tetracyanidoborate salt CuB(CN)₄

Abstract

The control of thermal expansion is essential in applications where thermal stability is required from fiber optics coatings, high performance fuel cell cathodes to tooth fillings. Negative thermal expansion (NTE) materials, although rare, are fundamental for this purpose. This work focuses on studying tetracyanidoborate salt CuB(CN)4, an interesting cubic-structure material that displays large isotropic NTE. A joint study of synchrotron X-ray diffraction, temperature-dependent Raman spectroscopy, and lattice dynamics calculations was conducted, showing that not only low-frequency optical modes (transverse thermal vibrations of N and C atoms) but also the acoustic modes (the vibrations of Cu atoms as a collective torsion of the neighboring atoms), contribute to NTE. As a result, new insights were gained into the NTE mechanism of CuB(CN)4 and related framework materials.

Exploring negative thermal expansion materials with bulk framework structures and their relevant scaling relationships through multi-step machine learning

“…149,150 Since the DFT calculations cannot take into account the contribution of entropic elasticity to NTE, there may be some deviations in calculating CNTE using both the static DFT calculations and ab initio molecular dynamics simulation with the machine learning interatomic potentials (MLIPs), compared to the experimental results. Nevertheless, our previous DFT calculations of CNTE for some NTE materials with framework structures (such as fluorides, [151][152][153][154] oxides, [155][156][157] cyanides 158 and PBAs [159][160][161] still have achieved comparable results with experiments, and it is shown that using the DFT calculations as a roughly qualitative criterion to judge whether a material has NTE characteristics should be reasonable and unquestionable. Due to the fact that the first-principles calculation of the CNTE will require a lot of computer time, especially for oxide systems with a large number of atoms in the primitive cells and complex crystal structures, here, we select a few compounds with simple structures and small number of atoms in the primitive cell for calculation.…”

Nanostructured Silver Films with a Low Coefficient of Thermal Expansion as a Promising Material for Nanoelectronics

“…[ 13–16 ] The introduction of layers with NCTE makes it possible to compensate for thermal stresses in functional systems. Also, materials with a thermal expansion close to zero, [ 17–19 ] which have broad prospects for using in modern technologies, [ 20,21 ] are very promising.…”