Understanding the role of guest molecules in the lattice void of open-framework structures is vital for tailoring thermal expansion. Here, we take a new negative thermal expansion (NTE) compound, TiCo(CN) 6 , as a case study from the local structure perspective to investigate the effect of H 2 O molecules on thermal expansion. The in situ synchrotron X-ray diffraction results showed that the as-prepared TiCo(CN) 6 •2H 2 O has near-zero thermal expansion behavior (100−300 K), while TiCo(CN) 6 without water in the lattice void exhibits a linear NTE (α l = −4.05 × 10 −6 K −1 , 100−475 K). Combined with the results of extended X-ray absorption fine structure, it was found that the intercalation of H 2 O molecules has the clear effect of inhibiting transverse thermal vibrations of Ti−N bonds, while the effect on the Co−C bonds is negligible. The present work displays the inhibition mechanism of H 2 O molecules on thermal expansion of TiCo(CN) 6 , which also provides insight into the thermal expansion control of other NTE compounds with open-framework structures.

No abstract

Negative thermal expansion (NTE) is an abnormal thermophysical phenomenon. Although NTE has been discovered in a growing number of materials, it is difficult to achieve both strong NTE and a wide operating temperature range in one material. In this work, the strong NTE of the oxide Cu 2 PVO 7 is reported in a wide temperature range (α v ∼ −26.01 × 10 −6 K −1 , 100−648 K), where the thermal expansion is highly anisotropic. The NTE capacity of Cu 2 PVO 7 is outstanding among the NTE framework structure oxides. Joint methods of high-resolution synchrotron X-ray diffraction, extended X-ray absorption fine structure, pair distribution function of synchrotron X-ray total scattering, density functional theory calculations, and maximum entropy model calculations were carried out to reveal the NTE mechanism of Cu 2 PVO 7 . Transverse vibrations of O atoms together with deformations of CuO 5 and P/VO 4 polyhedral units account for the rotation and twist among the polyhedra, leading to the NTE. The present work pushes forward progress in research regarding strong NTE oxides.

Negative or zero thermal expansion (NTE, ZTE) of materials is intriguing for the controllable thermal expansion. We report a series of orthorhombic α-Cu2-xZnxV2O7 (x = 0, 0.1, 0.2), in which...

No abstract