Dependence of mechanical properties of sapphire single crystal on crystallographic orientation was investigated with the tube-shaped samples. Three different parameters were measured: longitudinal sound waves speed, surface roughness and X-ray rocking curve width. The data show a strong correlation between the measured parameters. Evaluation of relative anisotropy coefficient for major orientation planes in sapphire possesses to characterize them as: C-plane – the most isotropic and the A-plane – the most anisotropic. C-plates (C-axis is normal to the plate face) have the highest isotropy and non-birefringence widely used in protective windows working under static or dynamic load. In addition high isotropy of C-plates helps to achieve the highest requirements to the window form (flatness, waveform distortion). Rather close results can be achieved on M-plates.

The maximal surface roughness and minimal sound speed characterize R-plane. This coincides with the minimal value of Young modulus in [01-12] direction. R-plane can be recommended for use under through thickness directed thermal gradient working conditions. The anisotropy of A-plates ([1-210] axis is normal to face) leads to aggravation of polished surface flatness and strength.

The experimental method proposed within this study has been proven to be effective in evaluation of angle dependence of different parameters of single crystals. Influence of both material non-homogeneity and machining conditions variation is minimal.

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