Negative Hydration Expansion in ZrW2O8: Microscopic Mechanism, Spaghetti Dynamics, and Negative Thermal Expansion

Abstract

We use a combination of X-ray diffraction, total scattering and quantum mechanical calculations to determine the mechanism responsible for hydration-driven contraction in ZrW${}_2$O${}_8$. Inclusion of H${}_2$O molecules within the ZrW${}_2$O${}_8$ network drives the concerted formation of new W--O bonds to give one-dimensional (--W--O--)${}_n$ strings. The topology of the ZrW${}_2$O${}_8$ network is such that there is no unique choice for the string trajectories: the same local changes in coordination can propagate with a large number of different periodicities. Consequently, ZrW${}_2$O${}_8$ is heavily disordered, with each configuration of strings forming a dense aperiodic `spaghetti'. This new connectivity contracts the unit cell \emph{via} large shifts in the Zr and W atom positions. Fluctuations of the undistorted parent structure towards this spaghetti phase emerge as the key NTE phonon modes in ZrW${}_2$O${}_8$ itself. The large relative density of NTE phonon modes in ZrW${}_2$O${}_8$ actually reflect the degeneracy of volume-contracting spaghetti excitations, itself a function of the particular topology of this remarkable material.

arXiv comment5 pages, 4 figures

References in corpus (6)

• The "Coulomb phase" in frustrated systems
• Design of crystal-like aperiodic solids with selective disorder--phonon coupling
• Analysis of a fully packed loop model arising in a magnetic Coulomb phase
• Negative Thermal Expansion in cubic ZrW2O8: Role of Phonons in Entire Brillouin Zone From ab-inito Calculations
• Orbital Dimer Model for Spin-Glass State in Y${}_2$Mo${}_2$O${}_7$
• Itinerant electrons in the Coulomb phase

Cited by in corpus (5)

• Water Adsorption in Soft and Heterogeneous Nanopores
• Anomalous thermal expansion and chiral phonons in BiB${}_3$O${}_6$
• Structure and magnetism of a new hexagonal polymorph of Ba${}_3$Tb(BO${}_3$)${}_3$ with a quasi-2D triangular lattice
• Effect of Hydration and Ammonization on the Thermal Expansion Behaviour of ZrW2O8: Ab-initio Lattice Dynamical Perspective
• Low energy phonons in single crystal ZrW${}_2$O${}_8$