Exploration Of Novel Tellurite Functional Crystals

The special three-dimensional periodic structures endow the crystals with rich and colorful characteristics of sound,light,electricity,magnetism and heat.Unlike natural crystal materials,artificial crystals are endowed with the concept of scientific regulation and design,which can be applied in different scenarios.They show their unique advantages in information communication,laser,semiconductor,new energy and other fields,and occupy an extremely important position in the field of functional materialsThe diversity of tellurite crystal structures makes it have the diversity of functions In recent years,tellurite functional crystal materials have shown excellent properties in second-order nonlinear optics,piezoelectricity,photorefraction and so on,which have attracted great attention from researchers at home and abroad.Our research goal is to explore novel acousto-optic crystals and nonlinear optical crystals with excellent properties in the tellurite system.This dissertation is divided into six chapters.The main contents of each chapter are as follows:In the first chapter,we mainly introduce acousto-optic crystals,nonlinear optical crystals and tellurite functional crystals,and propose the basis,purpose and main research contents of exploring functional tellurite crystalsIn the second chapter,we mainly introduce the reagents,solid-state synthesis,crystal growth methods and equipments,X-ray diffraction analysis,property characterizations,and first-principles calculations involved in the process of exploring functional tellurite crystalsIn the third chapter,a new type of acousto-optic crystal TiTe3O8 has been designed and grown by combining the advantages of the TeO2 crystal and the TiO2 crystal.So far,using Li2CO3-TeO2 as flux through a ? 100 mm crucible,the maximum size of the TiTe3O8 crystal can reach 65 mm × 55 mm × 35 mm,and the mass is 268.19 g.The crystal is transparent and the overall quality is good.The full-width at half-maximum of the rocking curve from the(400)plane of TiTe3O8 is only 55";the experimental density of the TiTe3O8 crystal is 5.626 g/cm3,reaching 98%of the theoretical density value.It indicates that the quality of the TiTe3O8 crystal grown by the flux method is excellent and can meet the requirements of characterizing the intrinsic physical properties.The thermal conductivity of the TiTe3O8 crystal increases from 3.321 W/(m·K)at 25 ? to 3.725 W/(m·K)at 300 ?,which is helpful for the acousto-optic application of the TiTe3O8 crystal at higher temperature.The bandgap of the TiTe3O8 crystal is about 3.37 eV.The TiTe3O8 crystal can maintain high transmittance of over 70%in the wavelength range of 600?5400 nm and high transmittance of over 60%in the wavelength range of 540?6000 nm.The refractive index values of the TiTe3O8 crystal in the wavelength range of 546.1?2325.4 nm were measured by the minimum deviation angle method and fitted by the Sellmeier equation.The acousto-optic figure of merit of the longitudinal wave propagating along[111]direction in the TiTe3O8 crystal is about 35 × 10-18 s3/g,which is comparable with that of the longitudinal wave propagating along[001]direction in the TeO2 crystal.Based on the TiTe3O8 crystal,a high-efficient acousto-optic modulator has been designed and constructed.The results indicate that the TiTe3O8 crystal is a potential new type of acousto-optic crystal material with excellent properties.In the fourth chapter,we design a new type of acousto-optic crystal ZrTe3O8 to solve the color problem of the TiTe3O8 crystal and extend acousto-optic applications in the visible wavelength range.So far,using Li2CO3-TeO2 as flux through a ? 70 mm crucible,the maximum size of the ZrTe3O8 crystal can reach 35 mm × 32 mm × 21 mm,and the mass is 56.33 g.The full-width at half-maximum of the rocking curve from the(004)plane of ZrTe3O8 is only 39",and the experimental density of the ZrTe3O8 crystal reaches 99%of the theoretical density.It indicates that the quality of the ZrTe3O8 single crystal grown by the flux method is excellent.We systematically study the thermal and optical properties of the ZrTe308 single crystal.The linear thermal expansion coefficient of the ZrTe3O8 crystal is 10.15 × 10-6 K-1 in the temperature range of 25?500 ?.The specific heat of the ZrTe3O8 crystal increases from 0.548 J/(g K)at 25 ? to 0.611 J/(g K)at 250?.The thermal diffusivity of the ZrTe3O8 crystal increases from 0.456 mm2/s at 25 ? to 0.496 mm2/s at 250 ?,and the thermal conductivity increases from 1.38 W/(m·K)at 250C to 1.67 W/(m.K)at 250 ?.The bandgap of the ZrTe3O8 crystal is about 4.30 eV.The UV cut-off edge of the ZrTe3O8 crystal is about 278 nm.The transmittance is over 70%in the wavelength range of 400?5800 nm,and the IR cut-off edge of the ZrTe3O8 crystal is about 7788 nm.The refractive index values of the ZrTe3O8 crystal decrease from 2.0889 to 2.0370 in the wavelength range of 632.8?1553 nm.First-principles calculations show that TeO4 polyhedra and ZrO6 octahedra play an important role in the optical properties of the ZrTe3O8 crystal.In the fifth chapter,based on the LiNbO3 crystal,a new type of nonlinear optical crystal Lii2ZrTeO6 has been designed and constructed by heterovalent substitution.At present,a Li2ZrTeO6 single crystal with sizes of 16 mm × 15 mm × 12 mm can be successfully grown by using Li2CO3-TeO2 as flux through ? 70 mm crucible.Li2ZrTeO6 belongs to a trigonal crystal system,R3 space group.The unit cell parameters are a=5.175(2)A,c = 13.857(6)A,V= 321.4(3)A3,Z= 3.Zr atoms and Te atoms in Li2ZrTeO6 occupy the lattice position of Nb atoms in LiNbO3.ZrO6 octahedra and TeO6 octahedra share corners to construct a three-dimensional structure framework.We characterize the quality of the(012)plane of Li2ZrTeO6 by Laue X-ray back-reflection diffraction apparatus.The diffraction patterns at different positions are symmetrical,clear and consistent,indicating that the overall quality of the crystal is excellent and can meet the requirements of the characterization of the intrinsic physical properties.The thermal conductivity of the Li2ZrTeO6 crystal at room temperature is 5.952 W/(m·K),which is comparable with that of the LiNbO3 crystal at room temperature(5.6 W/(m·K)),indicating that the Li2ZrTeO6 crystal has good thermal properties.We systematically study the linear and nonlinear optical properties of the Li2ZrTeO6 single crystal.The band gap of the Li2ZrTeO6 crystal is about 4.06 eV.The IR transmission cut-off edge of the Li2ZrTeO6 crystal is about 7.4 ?m,which is the widest nonlinear tellurite crystal reported so far.The laser damage threshold of the Li2ZrTeO6 crystal is 1300 MW/cm2,which is 22 times higher than that of the LiNbO3 crystal under the same conditions.It shows that the Li2ZrTeO6 crystal has outstanding optical damage resistant behavior and is suitable for high-power nonlinear optical applications.The Li2ZrTeO6 crystal is type-? phase-matchable,and exhibits a SHG efficiency approximately 2.5 times that of the KDP crystal.The results indicate that the Li2ZrTeO6 crystal is a potential nonlinear optical crystal First-principles calculations show that ZrO6 octahedra and TeO6 octahedra play a key role in the optical properties of the Li2ZrTeO6 crystal.In the sixth chapter,we summarize the main conclusions,innovations and further work to be studied.