Crystal Growth,thermal And Mechanical Properties Of TeO₂

When the ultrasonic wave propagates in the crystal,elastic stress is generated,which lead the refractive index of the crystal changes periodically and then ultrasonic grating is formed.The acousto-optic interaction will occur when light passes through the crystal which has ultrasonic grating.Thus,if a crystal has such acousto-optic effect,it is an acousto-optic crystal.Acousto-optic crystals are important component of acousto-optic devices such as acousto-optic modulators,acousto-optic tunable filters and acousto-optic deflectors.These acousto-optic devices have important applications in laser technology,optical signal processing and integrated optical communication technologies.At present,the common acousto-optic crystals are mainly TeO₂ crystal,PbMoO4 crystal,PbBr2 crystal,and HgCl2 crystal.Compared with other acousto-optic crystals,TeO₂ crystal has excellent sound and light excellent value not only due to its wide range of light transmission but also at?110?plane it has a lower shear wave speed of sound.Therefore,TeO₂ crystal is widely used in acousto-optic device in recent years.the sound and light excellent value is high.It is an ideal material for making all kinds of sound and light devices.In this paper,the growth process of TeO₂ single crystal and its influencing factors,such as thermal properties,mechanical properties and other physical properties are systematically studied.Our research mainly includes the following points:?1?Studied the effects of seed crystal orientation,temperature field distribution,growth rate and solid-liquid interface shape on the growth of TeO₂ crystal.Also,the crystal growth process parameters were optimized.The results show that the seed crystals in the[110]or[001]direction are selected,the temperature gradient is 25??50?/cm,the growth rate is 0.3mm/h?0.7 mm/h,the temperature of the TeO₂ crystal grown at the temperature drop rate of 25?45 ?/h.The TeO₂ crystal is???40 mm×110 mm,and the crystal form is intact,no cracking,and has high crystal quality.The average transmittance of the wavelength range of 300-3300 nm is 75%,and the half-width of the double rocking curve?FWHM?of the is 11".?2?The thermal properties of TeO₂ crystals were studied.the results show that when the temperature is between 305K and 778K,the spacing between atoms increases with the height of the temperature,resulting in thermal expansion of the crystal in the[100]direction and[001].The results show that when the temperature is between 305K?778K,the thermal expansion coefficient ?a in the[100]direction increases gradually between 1.47×10-6/K?22.7×10-6/K.The[001]direction thermal expansion rate increases gradually between 1.03×10-6/K?6.91×10-6/K.When the temperature reaches 450K,it gradually stabilizes.When the temperature reaches 450K,?a/?c?3.5.When the temperature changes between 300K and 675K,the a-axis thermal diffusion coefficient decreases slowly between 1.409 mm2/s?0.726 mm2/s,and the thermal diffusion coefficient of the c-axis decreases slowly between 1.957 mm2/s?0.916 mm2/s.The[100]direction and the[001]direction thermal conductivity decrease slowly between 3.27 W/?m.K??2.19 W/?m.K?,and between 4.17 W/?m.K??2.81 W/?m.K?.The internal heat conduction is dependent on the lattice vibration of the lattice wave and the movement of free electrons.The higher the temperature,the smaller the thermal conductivity.When the variation is in the range of 300K?675K,the specific heat value of[100]direction and[001]direction of TeO₂ crystal is 0.3727?J/?g*K???0.4727/?J/?g*K??,0.3697?J/?g*K???0.4632?J/?g*K??gradually increases.?3?The nanoindentation test was performed on the[100]and[001]oriented TeO₂ crystals,and the mechanical parameters such as elastic modulus and hardness were measured.When the applied load is 50mN?200mN,the hardness change in the[100]and[001]directions is gradually reduced between 5.445GPa?4.455 GPa and 4.664?4.156 GPa,and the elastic modulus is 56.76GPa?53.96 GPa and 88.494 GPa?81.623 GPa,reflecting the anisotropy of the TeO₂ crystal.The size effect of crystal hardness is analyzed by Meyer's law.The relationship between the applied load Pmax and the contact depth hc is obtained.The residual stress a₀ produced by the surface processing of the material can be obtained by the equation,a₀=-18.32834 in the[100]direction and a₀=-8.25085 in the[100]direction.