Strong Negative Thermal Expansion of Cu₂PVO₇ in a Wide Temperature Range

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 Thermal Expansion HfV2O7 Nanostructures for Alleviation of Thermal Stress in Nanocomposite Coatings

“…Most materials expand in volume in response to thermal excitation; the specific directionality and magnitude of expansion of a solid derives from a complex interplay of phonon dispersion, lattice structure, and electronic structure. , The Grüneisen parameter, a dimensionless number, clumps together different thermodynamic quantities in a singular metric that provides a population-averaged view of thermally triggered nonlinearities in phonon dynamics. , From a practical perspective, thermal expansion is strongly implicated in materials degradation because of stresses arising from thermal gradients. Such stresses are compounded during periods of prolonged operation, giving rise to fatigue and failure. , In laminar composites and coatings, differentials in the coefficient of thermal expansion (CTE) of different materials give rise to interfacial strain and debonding upon thermal cycling .…”

“…−7.0 × 10 –6 °C –1 in the range of 100–600 °C; however, an abnormal increase in NTE is observed above 600 °C as a result of a phase transition . The thermal expansion of ZrV 2 O 7 has been extensively tailored by substitution methods, such as single-site substitutions replacing V by P, Mo, and W, − or Zr by Hf and (Nb, Y), , as well as dual-site substitutions where Zr/V have been replaced by Fe/Mo, Fe/P, Cu/P, etc. ,, Substitution methods enable modulation of the temperature range of the NTE. For example, a phase-transition temperature as low as −48 °C is accessible with Mo substitution of ZrV 2 O 7 .…”

“…For example, a phase-transition temperature as low as −48 °C is accessible with Mo substitution of ZrV 2 O 7 . However, substitution can sometimes result in the diminution of the NTE coefficient and shrink the NTE window. ,, Furthermore, the intrinsic cubic symmetry of MV 2 O 7 is broken as a result of some substitutions, such as in the case of W-substituted and Cu/P-substituted MV 2 O 7 . , HfV 2 O 7 has been reported to have a somewhat higher CTE of ca. −7.2 × 10 –6 °C –1 as compared to ZrV 2 O 7 , but has hitherto been studied only within a limited temperature range .…”

“…1,2 The Gruneisen parameter, a dimensionless number, clumps together different thermodynamic quantities in a singular metric that provides a population-averaged view of thermally triggered nonlinearities in phonon dynamics. 3,4 From a practical perspective, thermal expansion is strongly implicated in materials degradation because of stresses arising from thermal gradients. Such stresses are compounded during periods of prolonged operation, giving rise to fatigue and failure.…”

“…21,22,24 Furthermore, the intrinsic cubic symmetry of MV 2 O 7 is broken as a result of some substitutions, such as in the case of W-substituted and Cu/Psubstituted MV 2 O 7 . 4,22 HfV 2 O 7 has been reported to have a somewhat higher CTE of ca. −7.2 × 10 −6 °C−1 as compared to ZrV 2 O 7 , but has hitherto been studied only within a limited temperature range.…”