Research Progress of Calcium Lanthanum Sulfide Transparent Ceramics for Supersonic Long-Wave Infrared Windows

doi:10.16552/j.cnki.issn1001-1625.2025.1139

Abstract

Abstract:

Infrared windows are critical components for supersonic aircraft optoelectronics systems， demanding exceptional infrared transmittance， thermal stability， and mechanical strength in extreme environments. Calcium lanthanum sulfide （CaLa₂S₄） transparent ceramics have emerged as a leading candidate beyond conventional materials such as oxide ceramics， fluorides， ZnS/ZnSe， due to their broad-band transmission （8~12 μm）， excellent rain erosion resistance， and mechanical robustness. This paper first elaborates on the origins of the excellent properties of CaLa₂S₄ ceramics， then focuses on reviewing the research progress in powder synthesis， sintering processes， and composition design of CaLa₂S₄ infrared transparent ceramics worldwide. It specifically analyzes the effects of fabrication processes including hot pressing （HP） sintering， spark plasma sintering （SPS）， and hot isostatic pressing （HIP） sintering on the optical and mechanical properties of CaLa₂S₄ infrared transparent ceramics. In addition， the sulfur loss issue during the sintering of CaLa₂S₄ ceramics is thoroughly discussed. However， challenges remain in China regarding near-net shaping of large components， controlling sulfur volatilization at high temperatures， and understanding defect dynamics. Future research must prioritize scalable production of high-transparency CaLa₂S₄， synergistic optimization of thermal-mechanical-optical properties， and validation under extreme conditions to enable their engineering application in supersonic flight.

Key words: CaLa₂S₄, infrared window material, transparent ceramics, ceramic fabrication process, optical quality

CLC Number:

TQ174.75⁺8.23

YANG Xi, ZHAO Hua, LIU Yonghua, HAN Bin, HE Kun, ZHOU Nianxi, MA Shiyue, HAN Tongyu, ZHOU Peng. Research Progress of Calcium Lanthanum Sulfide Transparent Ceramics for Supersonic Long-Wave Infrared Windows[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(3): 920-929.

Figures/Tables 6

Fig.1 Crystal structures of La2S3 with cubic-defect Th3P4 structure and CaLa2S4 with ideal Th3P4 structure［2］

Table 1 Physical properties of CaLa2S4 and ZnS［2，6，9-12］

Physical property	CaLa₂S₄	ZnS
Peak IR transmittance/%	68.4 （theoretical transmission at 10 μm）	Near 70 （experimental transmittance at 8~12μm）
Absorption coefficient at 10.6 μm/cm^-1	0.17	0.3
Hardness/（kg·mm^-2）	570	250
Flexural strength/MPa	86~106	60~103
Water drop impact	More resistant	—
Thermal expansion（200~400 ℃）/（10^-6 ℃^-1）	14.7	7.4
Thermal conductivity（20 ℃）/（W·m^-1·K^-1）	1.7	17.2

Fig.2 SEM image （a）， TEM image （b）， and energy spectrum （c） of CaLa2S4 powder synthesized via a wet chemistry method followed by thermal decomposition［22］

Fig.3 Calcium lanthanum sulfide samples of different La/Ca ratios exhibiting good optical transparency［30］

Fig.4 FTIR spectra of CaLa2S4 ceramic fabricated via cold pressing， cold isostatic pressing， hot pressing， and hot isostatic pressing synergistic technology［35］

Fig.5 （a） Mirror-polished NaLaS2 ceramic with ?20 mm×0.7 mm；（b） Infrared transmittance spectra of as-prepared NaLaS2 ceramic shown in （a） which corresponding to the curve a［45］

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