Single crystal sapphire possesses excellent optical, physical and chemical properties. It is the hardest oxide crystals, and remains high strength and chemical resistance at high temperatures. It also features a wide transmission wavelength range, great electrical insulation, and good thermal conductivity at low temperatures.
Physical Properties of Sapphire
Chemical formula
Al2O3（99.999%）
Crystal class
Hexagonal system, rhomboidal class 3m
Lattice constants, A
a=4.785, c=12.991
Density, g/cm3
3.98
Hardness
2000 with 2000 g identer
(Knoop)
9 (Mohs)
Optical transmission range, μm
0.17 - 5.5
Refractive index at 0.532 μm
no=1.7717, ne=1.76355
Water absorption
nil
Young Modulus, GPa
345
Shear Modulus, GPa
145
Bulk Modulus, GPa
240
Bending Modulus
(Modulus of Rupture), MPa
420 at 20 °C
280 at 500 °C
Elastic coefficient
C11=496, C12=164, C13=115, C33=498, C44=148
Poisson ratio
0.25-0.30
Friction coefficient
0.15 on steel
0.10 on sapphire
Thermal Properties of Sapphire
Meling point, K
2303
Specific heat, J/(kg x K)
105 at 91K
761 at 291K
Thermal coefficient of linear expansion, K-1, at 323K
6.66 x 10-6 parallel to optical axis 5 x 10-6 perpendicular to optical axis
Thermal conductivity, W/(m x K) at 300K
23.1 parallel to optical axis
25.2 perpendicular to optical axis
Electrical Properties of Sapphire
Resistivity, Ohm x cm at 200-500 °C
1011 - 1016
Dielectric constant
10.0
Dielectric strength, V/cm
4 x 105
Loss tangent
1 x 10-4
Transmission spectrum of 2 mm-thick sapphire window
Sapphire Refractive Index vs Wavelength
l, mm
No
Ne
0.193
1.92879
1.91743
0.213
1.88903
1.87839
0.222
1.87540
1.86504
0.226
1.87017
1.85991
0.244
1.85059
1.84075
0.248
1.84696
1.83719
0.257
1.83932
1.82972
0.266
1.83304
1.82358
0.280
1.82437
1.81509
0.308
1.81096
1.80198
0.325
1.80467
1.79582
0.337
1.80082
1.79206
0.351
1.79693
1.78825
0.355
1.79598
1.78732
0.442
1.78038
1.77206
0.458
1.77843
1.77015
0.488
1.77530
1.76711
0.515
1.77304
1.76486
0.532
1.77170
1.76355
0.590
1.76804
1.75996
0.633
1.76590
1.75787
0.670
1.76433
1.75632
0.694
1.76341
1.75542
0.755
1.76141
1.75346
0.780
1.76068
1.75274
0.800
1.76013
1.7522
0.820
1.75961
1.75168
0.980
1.75607
1.74819
1.064
1.75449
1.74663
1.320
1.75009
1.74227
1.550
1.74618
1.73838
2.010
1.73748
1.72973
2.249
1.73232
1.72432
2.703
1.719
1.711
2.941
1.712
1.704
3.333
1.701
1.693
3.704
1.687
1.679
4.000
1.674
1.666
4.348
1.658
1.65
4.762
1.636
1.628
5.000
1.623
1.615
5.263
1.607
1.599
Slide 1
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