Growth Of CaLa₂B₁₀O₁₉ Crystal

In this dissertation, the growth of nonlinear optical crystal, CaLa₂B₁₀O₁₉ (LCB) was focused. The major work consisted of: Measurement of the content of CaO,La₂O₃,B2O3 in the CaO-La₂O₃-B₂O₃ system., Investigation of the phase relation of the pseudo-binary LaB₃O₆-CaB₄O₇ system, Study on the kinetics in the CaLa₂B₁₀O₁₉-CaB₄O₇ system and the growth of LCB crystal. (1) The content of CaO,La₂O₃,B₂O₃ in the CaO-La₂O₃-B₂O₃ system were measured by chemical analysis. Ca²⁺,La³⁺ were separated by the pH=10 puffer solution and measured by the means of complexometric titration, the content of B₂O₃ was calculated. The recoveries of CaO,La₂O₃ were more than 98% and 98.5% respectively. The composition of CaLa₂B₁₀O₁₉ was determined. (2) Phase relationship of the LaB₃O₆-CaB₄O₇ pseudo-binary system was investigated by means of X-ray powder diffraction analysis and differential thermal analysis. In the system, there exists a compound of CaLa₂B₁₀O₁₉ except for LaB₃O₆ and CaB₄O₇. A peritectic reaction occurs at 1047℃,the compound of CaLa₂B₁₀O₁₉ melts incongruently to LaB₃O₆ and liquid. A eutectic reaction, among CaLa₂B₁₀O₁₉, CaB₄O₇ and liquid phase, occurs at 967℃and the composition of eutectic point is about 87mol% CaB₄O₇. According to the result, we successfully obtained the CaLa₂B₁₀O₁₉ single crystal from three high-temperature solutions with the compositions (molar ratio) of CaB₄O₇: CaLa₂B₁₀O₁₉=1:1, CaB₄O₇: CaLa₂B₁₀O₁₉=1.5:1 and CaB₄O₇: CaLa₂B₁₀O₁₉=2:1. (3) On the base of the find of a new calcium-lanthanunm borate crystal in the preceding experiment, when attempting to grow the CaLa₂B₁₀O₁₉ single crystal from the high-temperature solution with the composition of CaLa₂B₁₀O₁₉:CaB₄O₇ =1:1, the crystal was subject to wet chemical analysis and the result showed the chemical composition of the crystal is CaLa₂B₈O₁₆. Furthermore, We found the B₂O₃ was the volatile component in the solution and elucidated the relationship between the CaLa2B8O16 crystal formation and the volatility. Further supporting experiment was carried to directly obtain the CaLa2B8O16 crystal from the high-temperature solution with the composition of CaO:La2O3:B2O3=2:1:4. On contract, by adding more B2O3 to the solution with the composition of CaLa2B10O19:CaB4O7 =1:1, the stability of the solution was improved in the process to grow CaLa2B10O19. Among these solvents of B2O3 CaB4O7 and CaLa2B8O16, we chose suitable weight CaLa2B8O16 as solvent and obtained a transparent crystal with dimensions of 24 14 6mm3. Second harmonic generation effect of the crystal powder is nearly that of KDP. The crystal is chemical stable and not hygroscopic. (4) LCB single crystal were grown by the top seeded solution growth (TSSG) method using self-flux, The effect of the growth conditions, such as solutions composition, temperature gradient, cooling rate, rotation rate, seed direction, were investigated. An even temperature gradient in the axial direction over surface of solutions was required to avoid the erosion of the seed crystal. Low rotation and seeding in c direction were helpful to grow relative large LCB crystal, With careful control of the above parameters, clear crystals with relatively large were grown from the solution with the composition of CaLa2B10O19:CaB4O7 =1:1.5, and large crystal with relative clear were obtained from the solution with the composition of CaLa2B10O19:CaB4O7 :B2O3=1:1:0.7.