Does thorium(IV) oxide has a "fluorite" like structure? [closed]








**Closed.** This question is [off-topic](/help/closed-questions). It is not currently accepting answers.
 
 






---








 **Homework questions** must demonstrate some effort to understand the underlying concepts. For help asking a good homework question, see: [How do I ask homework questions on Chemistry Stack Exchange?](https://chemistry.meta.stackexchange.com/questions/141/how-do-i-ask-homework-questions-on-chemistry-stack-exchange)




Closed 5 months ago.








[Improve this question](/posts/173282/edit) 




> 
> The fluorite structure shows 8:4 coordination. Which of the following solutions has fluorite-like lattices?
> 
> 
> * $\ce{CaF2}$
> * $\ce{SrCl2}$
> * $\ce{BaF2}$
> * $\ce{ThO2}$?
> 
> 
> 


My book tells me only $\ce{CaF2}$, $\ce{SrCl2}$ and $\ce{BaF2}$ will have fluorite like structure. But should not $\ce{ThO2}$ also show fluorite like structure?




Thorium dioxide very much does have a fluorite structure. True, such a structure is more difficult to realize with oxides than with fluorides, for it requires a cation that is suffuciently large while having four positive charges. Thorium is one of the few metals that can make these constraints; [cerium is another](https://en.wikipedia.org/wiki/Cerium(IV)_oxide).


The fluorite structure also appears in compounds of magnesium with Group 14 elements, most commonly [$\ce{Mg2Si}$](https://en.wikipedia.org/wiki/Magnesium_silicide). In this case the four-coordinate element is the electropositive one (magnesium) rather than the electronegative one (fluorine in fluorite or oxygen in ceria/thoria), so the term "antifluorite" is often used to indicate the reversed bond polarity. Used currently in alloying of aluminum, magnesium silicide along with its (anti)fluorite counterparts having heavier Group 14 elements has been considered for thermoelectric applications.


 1

[here](https://materialsproject.org/materials/mp-643/) you can find the crystallographic date for $\ce{ThO2}$, which claimed to have fluoride type structure. The following reference provides supporting thermal expansion data for binary oxides with the fluorite, $\ce{MO2}$, and the antifluorite, $\ce{M2O}$, type structures. It states that:



> 
> This paper gives regression data for a modified second order polynomial fitted to the expansion data of, and percentage expansions for dioxides with (a) the fluorite and antifluorite structure: $\ce{AmO2, BkO2, CeO2, CmO2, HfO2, Li2O, NpO2, PrO2, PuO2, ThO2, UO2, ZrO2,}$ and (b) the rutile structure: $\ce{CrO2, GeO2, IrO2, MnO2, NbO2, PbO2, SiO2, SnO2, TeO2, TiO2}$ and $\ce{VO2}$. Reduced expansion curves for the dioxides showed only partial grouping into iso-electronic series for the fluorite structures and showed that the 'law of corresponding states' did not apply to the rutile structures.
> 
> 
> 


Thus, the author of your book have been mistaken to tell you that only $\ce{CaF2, SrCl2,}$ and $\ce{BaF2}$ have fluorite like structure. However, there are much more binary metal oxides may have fluorite like structure including your compound of interest, $\ce{ThO2}$.


**Reference:**


1. D. Taylor, "Thermal expansion data. II: Binary oxides with the fluorite and rutile structures, $\ce{MO2}$, and the antifluorite structure, $\ce{M2O}$," *Transactions and Journal of the British Ceramic Society* **198**4, *83(2)*, 32-37 (ISSN: 0307-7357).


 1