Lithium deficiency

B. Synthesis of Lithium-Deficient Mixed-Valent Clusters... 

In a review of naturally occurring dietary lithium (food and water sources), the author acknowledged that human lithium deficiency states have not been identified, but concluded that lithium should be considered an essential element, a conclusion reached on rather shaky grounds... 

Bach 1990 summarized the results with the comment There are animal studies which support lithium s role as a sine qua non for physical health in the case of goats and rats. The kids of lithium-deficient... 

Long-term lithium-deficiency experiments with female goats allowed an analysis of the influence of the lithium-poor nutrition on life expectancy. These data showed that 41% of Li-deficient goats and 7% of control animals died during the 2-year experiment. The oldest Li-deficient goats suffered from a disturbed hematopoiesis. Gallicchio et al. (1991) have described the influence of high lithium intake on hematopoiesis. 

SziiAgyi M, Anke M and SzentmihAlyi S (1985) The effect of lithium deficiency on the metabolism of goats. In Pais I, ed. New Results in the Research of hardly known Trace Elements. Horticultural University, Budapest, pp. 167-172. 

Note that we have a structure with a "built-in crystal defect, a vacancy. Both the lithium and niobium cations are in an octahedral coordination. In fact, the two ions, Li and Nb , have nearly the same radius and occupy octahedral sites with the same Cgy S5mimetry. The lithium deficiency in congruent crystals is accommodated by means of Nb anti-sites and Nb vacancies in a relative concentration that guaranties overall electrical neutrality. Note that many physical properties depend upon stoichiometry, e.g.- Curie temperature, absorption spectra, lattice parameters and photorefractive yield. 

Figure 8.5 shows the phase diagram for the hthium niobate system. There is a wide range of lithium deficiency in lithium niobate. Since electro-optic applications of this material require large crystals having a very uniform composition, it is essential that the congruent composition be known very accurately in order to grow... 

Cathode materials usually have complex stoichiometries as mentioned in section 1.0 above. Therefore, substantiation of the stoichiometries of the synthesized products is necessary. Often, the stoichiometries of the synthesized materials may not be exactly as calculated from molar ratio considerations. This is because the steps involved in the synthesis methods may introduce errors. For example, the weighing of the starting materials themselves is a crucial step and if not done carefully can be a serious source of error. Calcination procedures may also produce errors in stoichiometries due to certain processes such as Li vapourization at high temperatures of 850 °C and above producing lithium deficient materials (Ohzuku et al. 1990). The resulting final product may therefore be slightly different from the calculated values. That is why it is important to experimentally determine the stoichiometries of the final products. 

Figure 8.12 Band model ofthe electronic defects in slightly lithium-deficient Lii yFeP04 and lithium-containing FeP04. Upon changing the defect chemical reference point from FeP04 to LiFeP04, former conduction band now becomes the valence band. Reprinted with permission from Ref. 53, copyright 2011, John Wiley and Sons.

---