Page 62 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

IR-11.4 S O L I D S

IR-11.4.2 Indication of site occupancy
In a f ormula, the main symbols indicate the species present at a c ertain site, defined with
respect to empty space. T his will generally be the symbol of an element. If a s ite is vacant
this is denoted by the italicized symbol V. ( In certain contexts other symbols, such as a
square box, h, a re used for vacancies, but the use of italicized V is preferred, the element
vanadium being w ritten with the upright letter V).
The site and its occupancy in a s tructure of ideal c omposition are represented by right
lower indexes. The first index indicates the type of site, and the second index ( if used),
separated from the first by a c omma, i ndicates the number of atoms on this site. Thus,
an atom A o n a site normally occupied by A i n t he ideal s tructure is expressed by A A ; a n
atom A o n a site normally occupied by B i s e xpressed A B ; a nd M M,1 x N M,x M N,x N N,1 x
stands for a d isordered alloy, where the ideal composition is M M N N with all M a toms on one
type of crystallographic site and all N a toms on a s econd t ype of crystallographic site. An
alternative description is (M 1 x N x ) M (M x N 1 x ) N . A species occupying an interstitial site
(i.e. a site which is unoccupied in the ideal structure) is indicated by the subscript ‘i’.

Examples:
1. Mg Mg,2 x Sn Mg,x Mg Sn,x Sn Sn,1 x shows t hat in Mg 2 Sn some of the Mg atoms are
present on Sn sites and vice v ersa.
2. (Bi 2 x Te x ) Bi (Bi x Te 3 x ) Te shows t hat in Bi 2 Te 3 some o f t he Bi atoms are present on
Te sites and vice versa.

3. Na Na,1 x V Na,x Cl Cl,1 x V Cl,x shows that x Na and x Cl sites in NaCl are vacant, giving
Schottky defects.
4. Ca Ca,1 F F,2 x V F,x F i,x shows t hat in CaF 2 , x F s ites are vacant, while x F i ons are
situated on interstitial sites, creating Frenkel d efects.
5. (Ca 0.15 Zr 0.85 ) Zr (O 1.85 V 0.15 ) O , o r C a Zr,0.15 Zr Zr,0.85 O O,1.85 V O,0.15 , s hows that in
CaO-stabilized ZrO 2 , 0 .85 of the Zr sites are occupied by Zr, 0.15 of the Zr
sites are occupied by Ca, and that, of the two oxygen sites, 1.85 sites are occupied
by oxygen ions, leaving 0.15 sites vacant.
6. V V,1 C C,0.8 V C,0.2 shows that 0.2 C-sites are vacant i n v anadium c arbide, V C.

The defect symbols can be used in writing quasi-chemical reactions.

Examples:
7. Na Na ! V Na þNa(g) indicates the evaporation of a N a a tom, leaving behind
a s odium vacancy in the lattice.
8. 0.5Cl 2 (g)þV Cl ! Cl Cl indicates the incorporation of a c hlorine atom, from
a d ichlorine molecule, on a v acant chlorine site in the lattice.

IR-11.4.3 Indication of crystallographic sites

Crystallographic sites can be distinguished by subscripts, e.g. tet, oct and dod, denoting
tetrahedrally, octahedrally and dodecahedrally coordinated sites, respectively. The use of

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