Anomalous behaviour in the layer halides and oxyhalides of titanium and vanadium: a study of materials close to delocalisation

The authors have examined the MX 2 , MX 3 and MOX families (X=Cl,Br,I) of titanium and vanadium compounds magnetically, optically and structurally, as representatives of materials known to be close to d-electron delocalisation. They are interested in ascertaining the actual proximity of the various compounds to delocalisation, the effect of temperature upon the effective magnetic moments, the coexistence of single-electron with many-electron optical excitations and antiferromagnetism versus structural instability under metal-metal site interactions. In the MX 2 hexagonal layer family they also encounter the question of geometric frustration of antiferromagnetic order. Throughout, they question just how close their current one-electron band structure calculations are able to come in describing the electronic condition of these materials.