American Huilin Institute
According the ionocovalent model [1-3] the Lewis acid strengths have been considered as the ionocovalent function which partakes of properties bothof the ionic function and of the covalent function of the atoms. The ionic function has the property of the ionicity of ionization energy power from the nucleus of the atom omnidirectionally radiating and exerting on the valence electron cloud. The covalent functions has the property of the covalency localizing (confining) the ionization to an extent of ionocovalency on bonding. To express this duality, for a given cation, we took into account, (a) its polarizing power for the ionic part I(Zrk-2) and (b) its electronegativity for the covalent part C(Xz). The Lewis acid strengths can be defined as
Lz = z /rk2 – 7.7Xz + 8.0
The polarizing power of a cation is suggested to be equal to z/rk2, where z is the core charge, r is the ionic radius. Xz is the Zhang electronegativity. The Lz value gives a quantitative order of the relative Pearson hardness or softness for the various Lewis acids  and agrees fairly well with the previous classifications [4-7].”
Since then many methods and ideas derived from Zhang electronegativity Xz and Lewis acidLz:
1.1. Brown Lewis acid strength Sa
Brown (1988) derived an average Lewis acid strength Sa [8,9] from Zhang electronegativity XZ:
XZ = 1.118Sa + 0.771
which can be rewritten as
Sa = 1.18Xz - 0.653
where Xz is Zhang electronegativity, which gave Sa a physical definition and theoretical concepts.
1.2. Ionic-covalent Parameter ICP
Portier et al. [10-12] presented a new parameter based on the ionocovalent theory [1-3], the ionic-covalent parameter (ICP):
ICP = log(P) - 1.38X + 2.07
P is the polarizing power of the cation z/r2, as the ionic function, X is the Portier electronegativity [11,12], as the covalent function.
1.3. Lenglet’s RP Relationship
Based on the ionocovalent theory and the ICP [11,12], Lenglet proposed  “Ligand field spectroscopy and chemical bonding in Cr3+-, Fe3+-, Co2+- and Ni2+- containing oxidic solids”, referring to influence of the inductive effect of the competing bonds and magnetic interactions on the degree of covalency of the 3d M-O bonds, it has been shown that for transition metal oxides (3d3, 3d5, 3d7, 3d8, configurations), linear relationships are observed between either interelectronic repulsion or the Racah parameter (RP) and (i) the ionic covalent parameter ICPnn relative to the next nearest cationic neighbors outside the MOn polyhedra, and (ii) the optical basicity ^th calculated from the valence and coordination numbers of the component cations as proposed by Lebouteiller and Courtine .”
1.4. “Electron-acceptor-Strength” (EAS) Approach
Wen et al. reported [15,16] that the electron-acceptor strength (EAS) of the ionized donor centers, Mm+, decreases as the Lewis acid strength, Lz, of the element increases. Consequently, high mobilities, and thereby high conductivities, are likely to occur for ITO (or IO) samples heavily doped with donor centers having high Lz values, particularly in their oxidized form.
1.5. Scattering Cross Section Q
Marcel et al.[17-20] obtained the following expression for the scattering cross section Q
QGe4+/Qsn4+ = 0.55
It is interesting to note that for similarly heavily doped ITO and IGO (such as f and k) the value obtained above is close to the ratio calculated based on the Lewis acid strengths 
Lsn4+/LGe4+ = 0.53
It appears that when the factor dominating the mobility is the scattering of electrons from the ionized donor centers, Lz roughly varies inversely as Q.
This relationship can be also applied for other degenerate oxides having a predominant ionic-bond character as we have recently investigated.
[*] Zhang, Y.Ionocovalency and Applications. 2. IC-Lewis acid strengths，J. Am. huilin. Ins. 2011, 11, 1-10
[*] Zhang, Y. Ionocovalency, J. Am. huilin. Ins. 2011, 5, 1-11
[*] Zhang, Y. Ionocovalency and Applications 1. Ionocovalency Model and Orbital Hybrid Scales. Int. J. Mol. Sci. 2010, 11, 4381-4406