Geometric frustration

No attempt is made to be exhaustive and complete - the existing literature is too large for that to be practical. Instead, the basic principles will be outlined with minimal reference to theory and representative materials will be described with attention to structure, composition and magnetic properties characterisation. Several reviews exist which cover various stages in the development of the field of GFMM including those from the relatively early days, while there are more recent reviews of specific materials, such as pyrochlore oxides.  

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Many other mechanisms lead to energy dissipation, although they may be less universal than those related to boundary lubricant-induced geometric frustration. Chemical changes in lubricant molecules, reversible or irreversible, produce heat. Examples are configurational changes in hydrogen-terminated... 

While some disordered magnetic systems do display spin-glass behavior, those that are not geometrically frustrated can behave in a fundamentally different way. In... 

Explain the differences between geometric frustration, the spin-glass state, and Simpson s amorphous antiferromagnetism. 

Figure 52 AF spin correlations on plaquettes of square-planar, triangular, and tetrahedral geometries. (Ref 110. Reproduced by permission of Royal Society of Chemistry.) Plaquettea a, h, and e picmre geometrically frustrated situations...

Donor-r acceptor (D-rA) interactions. The combination of donor and acceptor sites raises the possibility of D A interactions (intramolecular and intermolecular). In most systems, such D A interactions are prevented by the steric demand of the substituents (steric frustration) and/or the nature of the organic linker (geometric frustration). Noticeable exceptions are illustrated in Scheme 1 (i) the Cj-bridged phosphine-alane 3 adopts a head-to-tail dimeric structure and is usually reacted in the presence of an additional Lewis base to displace the A1 interactions " (ii) the di- and tri-phosphine boranes 7 and 8 equilibrate in solution between open and closed forms which were unambiguously identified in the solid state by X-ray diffraction analyses (iii) the pyridine-borane 2 exists in solution as a mixture of closed monomeric form and head-to-tail dimeric structure, but N B interactions are readily cleaved upon coordination to Ru. ... 

In other more complex cases, the spins can take on a configuration that is not well approximated as a perturbed collinear configuration and such is the case for the spiral or helimagnetic ordering depicted in Figure 1. Noncollinear configurations are also observed in the family of so-called geometrically frustrated materials to be discussed later. 

Link 4. Comparison to Experiment for Liquid Crystals Liquid crystals and polymer glasses are really two faces of the same coin. In both cases e transition occurs because of a geometrical frustration arising from the stiffness of the chain. 

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