Growth And Property Characterizations Of Novel Boron/Phosphate Photoelectric Functional Crystals

The special three-dimensional space periodic structure endows crystals with rich and colorful specific properties of sound,light,electricity,magnetism,heat,and force.Unlike natural crystal materials,artificial crystals are endowed with the concept of scientific regulation and design,which can be targeted to serve in a variety of application scenarios,showing unique application advantages.In the artificial crystal materials,borate and phosphate crystals are the two types of photoelectric crystal materials that have been studied the deepest and the most.Over the past few decades,numerous boron and phosphate "star crystals" with excellent properties have been discovered and widely used in laser,nonlinear,piezoelectric,and birefringent fields.In this paper,we take boron and phosphate photoelectric functional crystals as the research object,aiming to develop new large-size photoelectric crystals and explore the potential application value of crystals in the fields of optics and electricity.The main research contents and conclusions are as follows:(i)Crystal growth and optical properties of Te2O(PO4)2Te2O(PO4)2 single crystal was grown by Czochralski method for the first time,and the technical problem that crystal was not easy to grow in the high-viscosity TeO2-P2O5 glass system was solved.In order to solve the color problem of the grown single crystal,the origin of the color center defect in the crystal was explored.Theoretical calculation and EPR test showed that the color center absorption of the brown crystal was mainly due to the defect of the oxygen vacancy in the crystal.After optimizing the growth parameters,high-quality transparent single crystal with a maximum size of 35 mm×30 mm×20 mm was finally successfully obtained.High-resolution X-ray diffraction rocking curve and Laue back-reflection patterns showed that Te2O(PO4)2 single crystal had high crystal quality.The optical properties of Te2O(PO4)2 crystal was characterized.The transmission spectra suggested that Te2O(PO4)2 crystal can transmit well from 0.29 to 4.70 ?m,and the band gap was about 4.30 eV.The laser damage threshold of the crystal is about 790 MW/cm2,which is greater than the KTP crystal.The optical SHG response of Te2O(PO4)2 was measured by means of the Kurtz-Perry method.The results showed that Te2O(PO4)2 was type-I phase-matchable and the SHG efficiency was about 1.3 times that of KDP.The refractive index of the crystal was measured by the minimum deviation angle method.The test result showed that the Te2O(PO4)2 crystal was a positive biaxial crystal.In the wavelength range of 0.4047?1.014 ?m,the birefringence is 0.13786?0.10615.The large birefringence ensures that the crystal can achieve type-I phase-matchable at 1064 nm.The relationship between the crystallographic axis and the optical principal axes of the crystal was determined using the refractive index data,and the angle between the c-axis and the X-axis was 29.1°.The thermal properties of Te2O(PO4)2 crystal have been studied.Te2O(PO4)2 crystal exhibits large thermal expansion anisotropy(?c/?a=4.05);in the range of 25-300?,the specific heat ranges from 0.511 J/(g·K)to 0.661 J/(g·K);at room temperature,the minimum thermal conductivity kc is 2.863 W/(m·K),and the maximum ka is 4.42 W/(m·K),which is greater than KTP crystal(2?3 W/(m·K)).First-principles calculations showed that the Te2O(PO4)2 crystal had a direct band gap,and optical properties mostly originated from the[TeO5]groups,and the contribution of[PO4]was small.(ii)Electric-elastic properties of Te2O(PO4)2The sample was designed according to the symmetry of the crystal and all the electroelastic constants of the Te2O(PO4)2 crystal were measured.Te2O(PO4)2 crystal has a relatively large piezoelectric constant.The longitudinal piezoelectric coefficient d33 is 6.6 pC/N,which is larger than the GaPO4(d11=4.50 pC/N)and AlPO4 crystal(d11=-3.30 pC/N),and is equivalent to the La3Ga5SiO14 crystal(d11=6.15 pC/N).In order to explore the application potential of Te2O(PO4)2 crystal in the field of high-temperature piezoelectricity,the high-temperature resistivity of Te2O(PO4)2 crystal along the X,Y,and Z axis and the high-temperature stability of the piezoelectric constant were tested.The results showed that Te2O(PO4)2 crystal had the largest resistivity along the Z-axis,and the resistivity along the X-axis was the smallest.At 300?,the resistivity along the Z direction is 7.0×109?·cm,which is about 9 times that of the La3Ga5SiO14 crystal.This showed that Te2O(PO4)2 crystal can meet the basic requirements of high temperature applications.With the increase of temperature,the piezoelectric constant d33 increases steadily.Compared to room temperature,the rate ofchange of the piezoelectric constant d33 at 475? is about 17.4%.The ferroelectricity test showed that Te2O(PO4)2 crystal was non-ferroelectric.In order to explore the correlation between crystal structure and piezoelectric properties,the dipole moment of Te2O(PO4)2 crystal was calculated and compared with GaPO4 and AlPO4 crystal.The calculation results showed that the dipole moment of the polyhedral groups in the Te2O(PO4)2 crystal was significantly larger than that of the GaPO4 and AlPO4 crystal,that was,the distortion degree of the ion groups in the Te2O(PO4)2 structure was greater.The relatively large piezoelectric properties of Te2O(PO4)2 crystal are mainly affected by the highly distorted[TeO5]polyhedron.(iii)Crystal growth and performance exploration of Te3O3(PO4)2A phosphate crystal Te3O3(PO4)2 with large birefringence was discovered for the first time,which exhibited an unexpectedly enhanced birefringence of 0.148 at 1064 nm,which hited a new high in inorganic phosphate materials.The centimeter-level Te3O3(PO4)2 single crystal was successfully grown using the Czochralski method.The rocking curve test showed that the obtained crystal was of high quality.The optical performance test showed that the Te3O3(PO4)2 crystal had a large band gap(4.3 eV),a wide transmission range(0.290?0.476 ?m)and a high laser damage threshold(544 MW/cm2).The birefringence of the crystal was measured with a polarizing microscope.The measured birefringence at 546.1 nm was 0.173,which was in good agreement with the calculation result of 0.183.Excellent physical properties and large birefringence indicated that Te3O3(PO4)2 was a potential phosphate birefringent material.The origin of the large birefringence of Te3O3(PO4)2 crystal has been emphatically explored.First-principles calculations and structural analysis show that the highly distorted[TeO5]group and the anti-parallel[PO4]pseudo-layer structure are the main reasons for the large birefringence of the Te3O3(PO4)2 crystal.Real-space atomcutting analysis show that the contribution of the[TeO5]group to the birefringence of Te3O3(PO4)2 crystal is about 66%,and the contribution of the[PO4]group is about 34%.This research provides a new strategy for the further design of new phosphate compounds with large birefringence.(iv)Crystal growth and performance exploration of Bi3TeBO9Centimeter-level Bi3TeBO9 single crystals were successfully grown using the flux method,and the appropriate flux system was determined,and the problem of melt delamination was overcome.The rocking curve test showed that the Bi3TeBO9 single crystal had high crystalline quality.The hardness test showed that the Vickers hardness of Bi3TeBO9 crystal was 664.98 kg/mm2 and the Mohs hardness was 5.89.The chemical stability test showed that Bi3TeBO9 crystal had good deliquescence resistance and acid corrosion resistance.The optical properties of Bi3TeBO9 crystal were studied.The band gap of Bi3TeBO9 crystal is 3.54 eV,and the UV cut-off edge is 0.350 ?m,and the infrared cut-off edge is 7.00 ?m.The laser damage threshold of the crystal is about 450 MW/cm2,closing to the KTP crystal.The optical SHG response was measured by means of the Kurtz-Perry method.The results showed the SHG efficiency of Bi3TeBO9 was about 1.6 times that of KDP.The refractive index of the crystal was calculated by first principles,and the result showed that Bi3TeBO9 was a negative optical uniaxial crystal with a birefringence of 0.058?0.026 at 0.532?1.064 ?m.The birefringence of Bi3TeBO9 crystal was tested with a polarizing microscope,and the birefringence at 546.1 nm was 0.063,which was close to the calculated result of 0.055.The correlation between crystal structure and performance was analyzed using first principles.The calculation results showed that Bi3TeBO9 crystal had an indirect band gap.The[BiO6]and[TeO6]group contributed the most to the optical properties of the crystal,and the[BO3]group contributed lessThermal characteristics test showed that the room temperature specific heat of Bi3TeBO9 crystal was 0.282 J/(g·K),which increased to 0.440 J/(g·K)at 400?;the thermal conductivity decreased from 2.010 W/(m·K)to 1.735 W/(m·K)at 25?300?.The electroelastic properties of Bi3TeBO9 crystal have been studied.Bi3TeBO9 crystal has a large piezoelectric constant,d33=24.4 pC/N,which is about 4 times that of La3Ga5SiO14 crystal and larger than LiNbO3 crystal.The dielectric constant ?11=18.42,?33=62.60.The elastic constant of the crystal was calculated using first principles,s33=15.33 pm2/N.The larger dielectric constant and elastic constant are the main reasons why the Bi3TeBO9 crystal exhibits a larger piezoelectric constant.In order to explore the application potential of Bi3TeBO9 crystal as a high-temperature piezoelectric crystal,the high-temperature resistivity of the crystal and the high-temperature stability of the piezoelectric constant were tested.At 450?,the resistivity of Bi3TeBO9 crystal along the X and Z directions are 9.0×107?·cm and 3.5×106 ?·cm,respectively.The resistivity in the X direction at 300? is 2.5×1010 ?·cm,which is about 30 times that of La3Ga5SiO14(8×108?·cm).The high temperature stability test of the piezoelectric constant showed that the piezoelectric constant d33 of Bi3TeBO9 crystal decreased slowly with the increase of temperature.Compared to room temperature,the rate of change of the piezoelectric constant at 475? is about 16.8%.The ferroelectricity test showed that Bi3TeBO9 was non-ferroelectric.Pr:Bi3TeBO9 single crystal was grown by the flux method.EPMA test showed that the doping concentration of Pr3+,was 1.85×1021 ions/cm3.The optical properties of the crystal were investigated.The absorption spectrum showed that the Pr:Bi3TeBO9 crystal had a relatively large absorption cross section and FWHM.Based on Judd-Ofelt theory,the oscillator strengths,radiative transition probabilities,branching ratios,and radiative lifetime were calculated.The J-O parameters were determined to be:?2=2.28×1020 cm2,?4=4.17×1020 cm2,and ?6=3.09×1020 cm2.In addition,the Pr:Bi3TeBO9 crystal has a large emission cross section.The emission cross sections for the 3P0?3F4 transition at 734 nm was calculated to be 19.6×10-19 cm-2.Preliminary research shows that Pr:Bi3TeBO9 crystal may be an ideal material for the preparation of red-light solid-state lasers.