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Ge, germanium
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Elastic constants cij (1011 dyn/cm2 or 1010 Pa):
13 4.9 4.9 0 0 0
4.9 13 4.9 0 0 0
4.9 4.9 13 0 0 0
0 0 0 6.7 0 0
0 0 0 0 6.7 0
0 0 0 0 0 6.7
Photoelastic constants pij:
-0.154 -0.126 -0.126 0 0 0
-0.126 -0.154 -0.126 0 0 0
-0.126 -0.126 -0.154 0 0 0
0 0 0 -0.073 0 0
0 0 0 0 -0.073 0
0 0 0 0 0 -0.073
Sound velocity:
direction polarization v (105 cm/s)
[100] [100] 4.99
[110] [110] 5.41
[111] [111] 5.5
[100] S 3.55
[110] [1-10] 2.75
[111] S 3.04
Acousto-optic figure of merit:
sound dir. sound pol. light dir. light pol. M (10-18 s3/g)
[111] [111]   [111] 840
[100] [010]   arb. 290

Refraction indices:
l (mkm) nx ny nz
1.8 4.143 4.143 4.143
1.9 4.129 4.129 4.129
2 4.116 4.116 4.116
2.1 4.104 4.104 4.104
2.2 4.092 4.092 4.092
2.3 4.085 4.085 4.085
2.4 4.078 4.078 4.078
2.5 4.072 4.072 4.072
2.6 4.068 4.068 4.068
2.998 4.0453 4.0453 4.0453
3.303 4.037 4.037 4.037
3.419 4.0336 4.0336 4.0336
4.258 4.0217 4.0217 4.0217
4.866 4.017 4.017 4.017
6.238 4.0092 4.0092 4.0092
8.66 4.0036 4.0036 4.0036
9.72 4.0026 4.0026 4.0026
11.04 4.002 4.002 4.002
12.12 4.0018 4.0018 4.0018
13.02 4.0016 4.0016 4.0016
14.21 4.0015 4.0015 4.0015
15.08 4.0014 4.0014 4.0014
16 4.0012 4.0012 4.0012

NOTE: It should be taken into account that nx=ny=nz=n for optically isotropic material and nx=ny=no and nz=ne for uniaxial crystal.		 Crystal symmetry: m3m
Density: 5.3267 g/cm3
Optical spectral range: 1.5 - 22 mkm
NOTE: In those cases when different researchers give distinct values of constants, avaraged data are presented in Tables.

Source: Dept. of Physics of MSU