3.1 Mixing Elements
37
in which they contribute more than one electron to the formation of covalent bonds.
Hence the most probable cause of their wide deviation is the assumption of screening
constants of unity for all electrons except the one in the final shell.”
The value of n in binary compounds, n
∗ , is discussed on the basis of the estimation
of the electronegativity of radical AB [3] and is expressed by the following equation
(obtained by inserting p = s = 1 in Eq. (6) in Ref. [1]).
n
∗
= (n A − 1) + 3
χ A
χ A + χ B
(3.2)
By substituting n
∗ in Eq. (3.2) for n in Eq. (3.1), expressing the effective radius r
in Eq. (3.1) using the bonding length d (= 2r), and substituting the value of d for that
of element A, d A , the work function of a binary compound can be expressed using
the following equation.
χ AB = χ A +
0.62
d A
3χ A
χ A + χ B
− 1
(3.3)
Combining Eqs. (3.3) and (2.8) gives the work function of binary compound AB
as
φ AB = φ A +
1.41
d A
2φ A − φ B − 0.34
φ A + φ B − 0.68
.
(3.4)
In Fig. 3.3, thus calculated values of φ AB are shown with experimental values
taken from Ref. [1].
Fig. 3.3 Calculated work
function versus measured
work function for various
binary systems [1]
1.0
3.0
4.0
5.0
6.0
7.0
2.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Ni-O W-N Mn-O
Pd-O
W-H
W-O
W-Be
Zr-O
Fe-H
Hf-O
Ni-H
Co-H
Ta-N
Ta-H
Zr-Cl
Ti-Cl
Zr-Ce
Hf-Cs
Cu-Ba
W-Zr
Mo-Th
Ta-Th
Ni-Ba
W-La W-Y
W-Ca
W-Li
Ag-Ba
W-Sr
Ni-Cs
Ta-Cs Ti-Cs
Mo-Cs
C-Cs
Ф (eV) (calculated)
Ф (eV) (measured)
0