Growth of 2~3 Inch Magnesium-Doped Near-Stoichiometric Ratio Lithium Tantalate Crystals

doi:10.16553/j.cnki.issn1000-985x.2025.0044

Abstract

Abstract: Magnesium-doped near-stoichiometric ratio lithium tantalate （MgO∶SLT） crystals exhibit significant application potential in ultraviolet single-photon detection and high-power frequency conversion laser， owning to their outstanding nonlinear optical property， large laser damage threshold， and high transmittance in the ultraviolet band at 270 nm. However， it is very difficult to grow the single crystal from lithium-rich raw materials due to lithium volatilization and compositional segregation. In this study， 2~3 inch （1 inch=2.54 cm） SLT and MgO∶SLT crystals were successfully grown by the optimized Czochralski method with a high-pressure ambient atmosphere or a flowing gas system. It was demonstrated that the SLT crystal has a lithium-tantalum component ratio of about 49∶51， which is higher than the lithium component content in conventional congruent lithium tantalate crystals. MgO∶SLT crystal grown from the same lithium-rich melt have a magnesium concentration of Mg/Ta molar ratio about 1.47%， and the effective segregation coefficient of magnesium reaches 1.69. MgO∶SLT crystal maintain an optical transmittance of more than 65% in a wide spectral range from 270 nm to 800 nm， and the coercive field reduce to 2.8 kV/mm. Meanwhile， the room-temperature thermal conductivity of MgO∶SLT crystals along the Z-axis reaches 7.34 W/（m·K）， which is about 61.7% higher than that of conventional magnesium doped congruent lithium tantalate crystals.

Key words: magnesium-doped lithium tantalate crystal; near-stoichiometric ratio; crystal growth; solar-blind ultraviolet region; nonlinear optical

CLC Number:

LIU Shouting, WEN Xujie, HAN Wenbin, LI Chenzhe, SONG Wei, CUI Jiangang, SONG Song, LI Yong, SUN Dehui, LIU Hong. Growth of 2~3 Inch Magnesium-Doped Near-Stoichiometric Ratio Lithium Tantalate Crystals[J]. Journal of Synthetic Crystals, 2025, 54(8): 1396-1402.

Figures/Tables 10

Fig.1 XRD pattern of furnace wall volatiles （a） and photo of 3-inch SLT crystal （b）

Fig.2 SLT crystal photo grown in high pressure in nitrogen （a） and XRD patterns of copper coil corrosives （b）

Fig.3 2-inch MgO∶SLT crystals （a） and wafers （b） growth in a flowing gas environment

Table 1 Curie temperatures of SLT and MgO∶SLT crystals and corresponding polycrystalline composition

Sample

Polycrystalline material composition

Curie temperature/℃

Magnesium concentration in crystals

SLT

Li/Ta molar ratio is 58.6/41.4

626.92 （head）

626.49 （tail）

—

MgO∶SLT

Li/Ta molar ratio is 58.6/41.4

Mg/Ta molar ratio is 1%

625.59

Mg/Ta molar ratio is 1.47%

Fig.4 High-resolution XRD patterns of SLT （a） and MgO∶SLT （b） crystals

Fig.5 Absorption coefficient （a） and transmission curves （b） of SLT and MgO∶SLT crystal

Table 2 no and ne of SLT and MgO∶SLT crystals@633 nm

Sample	n_o	n_e
SLT	2.177 25	2.175 12
MgO∶SLT	2.176 26	2.174 53

Fig.6 Hysteresis loop of MgO∶SLT crystal

Fig.7 Variation law of thermal conductivity in X and Z axes of MgO∶SLT crystal with temperature

Table 3 Room temperature thermal conductivity of MgO∶SLT and MgO∶CLT crystals

Thermal conductivity/（W·m^-1·K^-1）	MgO∶SLT	MgO∶CLT*
k_x	5.90	3.83
k_z	7.34	4.54

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