Frustrated soft modes and negative thermal expansion in ZrW2O8.

Soft manifold dynamics behind negative thermal expansion.

Minimal models are developed to examine the origin of large negative thermal expansion in underconstrained systems. The dynamics of these models reveals how underconstraint can organize a thermodynamically extensive manifold of low-energy modes which not only drives negative thermal expansion but extends across the Brillioun zone. Mixing of twist and translation in the eigenvectors of these mod...

Unusual low-energy phonon dynamics in the negative thermal expansion compound ZrW2O8.

An infrared study of the phonon spectra of ZrW2O8 as a function of temperature which includes the low-energy (2-10 meV) region relevant to negative thermal expansion is reported and discussed in the context of specific heat and neutron density of state results. The prevalence of infrared active phonons at low energy and their observed temperature dependence are highly unusual and indicative of ...

Synthesis and thermal expansion properties of ZrO2/ZrW2O8 composites

In this work, a ceramic composite of ZrW2O8 and ZrO2 was synthesized, in order to investigate the possibility of compensating the positive thermal expansion of ZrO2 with the negative thermal expansion (NTE) compound ZrW2O8, tailoring the thermal expansion of these composites. The NTE material was mixed with varying amounts of ZrO2. The thermal expansion coefficients of this series of composites...

Geometrical Origin and Theory of Negative Thermal Expansion in Framework Structures

By framework structures are meant materials consisting of relatively stiff units such as octahedra or tetrahedra, joined by shared oxygen (or other) atoms at the corners. Examples are ZrW2O8 and many aluminosilicates. Rigid rotation of the units often gives a reduction of the volume or of some lattice constant as a purely geometrical effect. The theory of this effect is developed and shown to g...

The Route to Negative Thermal Expansion in ZrW2O8