偏硼酸钙晶体的热学性能研究

doi:10.16553/j.cnki.issn1000-985x.2026.0020

摘要/Abstract

摘要： 偏硼酸钙（Ca（BO₂）₂， CB₂）晶体因具有较大的双折射率、较短的紫外透过截止边和较高的紫外波段透过率，被认为是一种具有广泛应用前景的深紫外双折射晶体。晶体的热学性能对其生长及应用极为重要，但CB₂晶体的热学性能尚未系统研究。本文对提拉法生长的CB₂晶体的热膨胀系数、比热容、热扩散系数及热导率等热学性能进行了系统研究。结果表明，在323~723 K，CB₂晶体沿a、b、c轴的平均热膨胀系数分别为α₁₁=4.52×10^-6 K^-1，α₂₂=3.44×10^-6 K^-1，α₃₃=2.91×10^-5 K^-1，具有较大热膨胀各向异性，在晶体生长过程中更容易发生开裂。在298~723 K，晶体比热容为0.937~1.242 J/（g·K），热扩散系数为A₁₁=0.734~1.755 mm²/s，A₂₂=2.199~4.361 mm²/s，A₃₃=0.529~1.196 mm²/s。根据热扩散系数、比热容及理论密度，计算得到晶体在相同温度范围（298~723 K）内的热导率分别为κ₁₁=2.366~4.353 W/（m·K），κ₂₂=7.089~10.818 W/（m·K），κ₃₃=1.781~3.088 W/（m·K）。

关键词: 热学性能; 偏硼酸钙; 双折射晶体; 热膨胀系数; 热扩散系数; 热导率

Abstract: Deep ultraviolet （DUV） light sources have promising application prospects in fields such as ultraviolet lithography， high-resolution spectroscopy， precise microfabrication， biomedicine， ultra-sensitive detection， and photochemistry. In practical applications， it is necessary to use deep ultraviolet birefringent devices such as polarizer/beam splitter， polarization beam splitter， phase retarder， optical isolation， and beam displacement to generate， modulate， separate and control polarized light. Currently， there is an extremely limited supply of commercial birefringent crystals suitable for the deep ultraviolet wavelength range. Calcium metaborate（Ca（BO₂）₂， abbreviated as CB₂） crystal is considered as a kind of deep ultraviolet birefringent crystal with promising application prospects， due to their large birefringence， short ultraviolet transmission cutoff edge and high ultraviolet band transmittance. Although the thermal properties of crystals are of paramount importance for both bulk crystal growth and subsequent device applications， the thermal behavior of CB₂ crystal has not yet been systematically investigated. Previously， only limited thermal data were available， with merely the thermal expansion coefficient reported within a narrow temperature range from 323 K to 873 K. CB₂ crystals were grown by the Czochralski method， and their thermal properties were systematically studied in this study. The thermal expansion coefficient was measured employing thermal dilatometer， specific heat capacity and thermal diffusivity were characterized by laser flash analyzer along different principal crystallographic directions. Thermal conductivity was calculated combining the measured specific heat capacity， thermal diffusivity， and the theoretical density of the crystal. The research results indicate that thermal expansion of the CB₂ crystal exhibits obvious anisotropy， and the average thermal expansion coefficients along the crystallographica，b， andc axes respectively areα₁₁=4.52×10^-6 K^-1，α₂₂=3.44×10^-6 K^-1 andα₃₃=2.91×10^-5 K^-1 within the temperature range from 323 K to 723 K. The microstructure analysis indicates that this is mainly attributed to the differences in the strength of chemical bonds along the different crystallographic axes. specific heat capacity shows a steadily increasing trend as a whole， ranging from 0.937 J/（g·K） to 1.242 J/（g·K）， indicating that it has a relatively high laser damage threshold. The thermal diffusivity and thermal conductivity gradually decrease as the temperature rises. Within the temperature range from 298 K to 723 K， the thermal diffusivities areA₁₁=0.734~1.755 mm²/s，A₂₂=2.199~4.361 mm²/s andA₃₃=0.529~1.196 mm²/s， respectively. Correspondingly， the calculated thermal conductivities areκ₁₁=2.366~4.353 W/（m·K），κ₂₂=7.089~10.818 W/（m·K） andκ₃₃=1.781~3.088 W/（m·K）， respectively. The thermal conductivity of CB₂ crystal also exhibits strong anisotropy. Due to the strong covalent bond （B—O bond） connecting along theb-axis direction， the phonon group velocity is extremely high in this specific direction， resulting in the maximum thermal conductivity. The research results of this paper provide detailed and reliable basic data for optimizing the temperature field design of single crystal growth， suppressing crystal cracking， and designing the thermal management for deep ultraviolet high-power optical devices.

Key words: thermal property; calcium metaborate; birefringent crystal; thermal expansion coefficient; thermal diffusivity; thermal conductivity

中图分类号:

O736

黄云棋, 杨金凤, 王小闯, 张博, 孙军, 潘世烈. 偏硼酸钙晶体的热学性能研究[J]. 人工晶体学报, 2026, 55(5): 682-688.

HUANG Yunqi, YANG Jinfeng, WANG Xiaochuang, ZHANG Bo, SUN Jun, PAN Shilie. Thermal Properties of Ca(BO₂)₂ Crystals[J]. Journal of Synthetic Crystals, 2026, 55(5): 682-688.

图/表 5

图1 CB2晶体热膨胀率随温度变化曲线

Fig.1 Temperature dependence of thermal expansion of CB2 crystals

图2 CB2晶体结构示意图［12］

Fig.2 Schematic diagram of CB2 crystal structure［12］

图3 CB2晶体比热容随温度变化曲线

Fig.3 Temperature dependence of specific heat capacity of CB2 crystals

图4 CB2晶体热扩散系数随温度变化曲线

Fig.4 Temperature dependence of thermal diffusivity of CB2 crystals

图5 CB2晶体热导率随温度变化曲线

Fig.5 Temperature dependence of thermal conductivity of CB2 crystals

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