Growth of BPO4 Crystals from Li2O-B2O3 Flux

doi:10.16553/j.cnki.issn1000-985x.2026.0044

Abstract

Abstract: BPO₄ crystal has attracted considerable interest as a nonlinear optical （NLO） material due to its extremely short ultraviolet （UV） cutoff edge，strong powder second-harmonic generation （SHG） response，and high physicochemical stability. In this work，high-quality BPO₄ single crystals were successfully grown via the top-seeded solution growth （TSSG） method employing a Li₂O-B₂O₃ flux，and their crystalline quality，optical properties，and mechanical properties were systematically investigated. The Li₂O-B₂O₃ flux system exhibits low volatility and remains transparent at high temperatures，enabling real-time monitoring of the growth process. The as-grown crystals show a narrow rocking curve with a full width at half maximum （FWHM） of 0.008°，confirming the efficacy of this flux in producing high quality crystals. Raman and infrared spectroscopy are carefully elucidated to confirm the ion group in the BPO₄ crystal. Optical transmission measurements reveal that the crystal possesses a broad transparent range，with UV and IR cutoff edges extending to 133 and 4 270 nm，respectively，underscoring its potential for deep-UV applications. Furthermore，nanoindentation tests demonstrate its robust mechanical stability，yielding a hardness of approximately 12.75 GPa and a reduced modulus of about 153.37 GPa. In summary，Li₂O-B₂O₃ flux exhibits low volatility and high solution transparency，proving to be an excellent medium for the growth of high-quality BPO₄ crystals. The combination of an extremely short UV cutoff edge，wide spectral transparency，and favorable mechanical properties positions BPO₄ as a promising candidate for next-generation deep-UV NLO materials.

Key words: BPO₄ single crystal; nonlinear optical crystal; top-seeded solution growth method; flux system; optical property; mechanical property

CLC Number:

O782⁺.4

PAN Jiayue, JING Fangli, LIU Hongjun, HU Zhanggui, WU Yicheng. Growth of BPO₄ Crystals from Li₂O-B₂O₃ Flux[J]. Journal of Synthetic Crystals, 2026, 55(6): 843-850.

Figures/Tables 11

Fig.1 Photographs of BPO crystals

Fig.2 XRD patterns

Fig.3 Rocking curves of BPO crystal

Table 1 Doping concentrations in BPO crystal

System	Doping element	Doping concentration/%
Li₂O-B₂O₃	Li	1.357
Li₂O-MoO₃	Li	2.219
Li₂O-MoO₃	Mo	6.910

Fig.4 XPS spectra of BPO crystals

Fig.5 FT-IR spectrum of BPO crystal

Fig.6 Raman spectrum of BPO crystal

Fig.7 Transmission curves of BPO crystals

Fig.8 Loading-unloading curves of BPO crystals

Table 2 Hardness and reduced modulus of BPO crystals

Sample	H/GPa	E_r/GPa
1	12.35	139.11
2	11.78	144.83
3	12.53	150.27
4	13.87	176.08
5	11.55	146.65
6	15.43	163.28

Fig.9 Elastic recovery rate of BPO crystals

References 21

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Growth of BPO₄ Crystals from Li₂O-B₂O₃ Flux

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