Disordered cation compounds

Li2MCl4 compounds undergo a phase transition to a disordered cation-deficient rocksalt-structured form (space group Fm3m), in which the two cation species are randomly distributed over all the oct sites, which then have an average occupancy of 4 [132, 133]. 

Modifiers in glass are compounds that tend to donate anions to the network, whereas the cations occupy "holes" in the disordered stmcture. These conditions cause the formation of nonbridging anions, or anions that are connected to only one network-forming cation, as shown in Figure 2. Modifier compounds usually contain cations with low charge-to-radius ratios (Z/r), such as alkali or alkaline-earth ions. 

In all cases, broad diffuse reflections are observed in the high interface distance range of X-ray powder diffraction patterns. The presence of such diffuse reflection is related to a high-order distortion in the crystal structure. The intensity of the diffuse reflections drops, the closer the valencies of the cations contained in the compound are. Such compounds characterizing by similar type of crystal structure also have approximately the same type of IR absorption spectra [261]. Compounds with rock-salt-type structures with disordered ion distributions display a practically continuous absorption in the range of 900-400 cm 1 (see Fig. 44, curves 1 - 4). However, the transition into a tetragonal phase or cubic modification, characterized by the entry of the ions into certain positions in the compound, generates discrete bands in the IR absorption spectra (see Fig. 44, curves 5 - 8). 

The defects of the matrix play an important role on luminescent performances in these materials. Taking into consideration the preparation process of these compounds with the solid-state reaction of mixtures of BaC03, H3BO3, and NH4H2PO4 at different molar ratio, non-equal evaporation during the sintering process of these powders is inevitable and thus results in the formation of intrinsic defects, such as cation and oxygen vacancies. Positional disorder of B and Vacant B (Vb)" have been reported in SrBPOs crystals on the basis of... 

Cul) is not due to point defects but to partial occupation of crystallographic sites. The defective structure is sometimes called structural disorder to distinguish it from point defects. There are a large number of vacant sites for the cations to move into. Thus, ionic conductivity is enabled without use of aliovalent dopants. A common feature of both compounds is that they are composed of extremely polarizable ions. This means that the electron cloud surrounding the ions is easily distorted. This makes the passage of a cation past an anion easier. Due to their high ionic conductivity, silver and copper ion conductors can be used as solid electrolytes in solid-state batteries. 

Although combined with [Ni(dmit)2], none of the above-mentioned compounds exhibit electrical properties, since they are 1 1 materials without any charge transfer. One of the first attempts to obtain fractional oxidation state compound was performed by us in 2006 [101]. [Fe(sal2-trien)][Ni(dmit)2]3 has been obtained by electrocrystallization from an acetonitrile solution of [Fe(sal2-trien)][Ni(dmit)2], This compound behaves like an SC (ctrt = 0.1 S cm ) but does not exhibit any spin transition. This seems to be due to the statistical disorder of the whole Fem complexes, which prevents the occurrence of short contacts between cations. 

The natural and synthetic compounds differ in the arrangement of cations in both compounds the anion packing is disordered. Feroxyhyte is a disordered form of the synthetic material with the cations being distributed almost entirely randomly over the interstices. 

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