(Oxy)sulfide materials possess unique combination of physico-chemical properties (high thermal and chemical stability, large domain of transparency, low phonon energy….) making them ideal candidates for both active and passive optical applications. However, among them, only zinc sulphide (ZnS) is commercialized as infrared optics. Sintering polycrystalline ceramic materials to transparency is a very challenging task. Transparency of ceramics is indeed highly influenced by light scattering on residual pores, inclusions of secondary phases or impurities and, in the case of birefringent materials, light scattering by randomly oriented birefringent grains. Special attention should be paid, in particular, to the synthesis methods in order to satisfy powder purity and powder size requirements. For this reason, little research has succeeded in the quest for new infrared transmitting materials. This presentation addresses recent developments on the processing of (i) ZnS with improved hardness in comparison to commercial products (ii) CaLa2S4 and BaLa2S4 of cubic Th3P4-type and (iii) hexagonal La2O2S. The properties that have been investigated are primarily related to their application as infrared window materials, i.e. optical and mechanical. The presentation aims to understand the relationship between processing and subsequent microstructure of the ceramics and their optical and mechanical properties. References [1] C. Chlique, O. Merdrignac-Conanec, N. Hakmeh, X.H. Zhang, J.-L. Adam, Transparent ZnS ceramics by sintering of high purity monodisperse nanopowders, J. Am. Ceram. Soc., 96 [10] (2013) 3070–3074 [2] N. Hakmeh, O. Merdrignac-Conanec, X-H. Zhang, Method of manufacturing a sulfide-based ceramic element particularly for IR-optics applications, Application number: EP2966051 (A1) (2014), International Publication Number WO 2016/005439 (A1) [3] O. Merdrignac-Conanec, G. Durand, S. Walfort, N. Hakmeh, X-H. Zhang, Elaboration of CaLa2S4 transparent ceramics from novel precursor powders route, Ceram. Int. 43 (2017) 5984-598 [4] Lettre Innovation du CNRS n° 64 https://www.cnrs.fr/lettre-innovation/actus.php?numero=689 [5] G. Durand, N. Hakmeh, V. Dorcet, V. Demange, F. Cheviré, O. Merdrignac-Conanec, New insights in structural characterization of transparent ZnS ceramics hot-pressed from nanocrystalline powders synthesized by combustion, J. Eur. Ceram. Soc. 39 (2019) 3094-3102 [6] G.R. Durand, Q. Bizot, S. Quéméré, M. Pasturel, X-H. Zhang, O. Merdrignac-Conanec, Processing of CaLa2S4 infrared transparent ceramics : a comparative study of HP and FAST/SPS techniques, J. Am. Ceram. Soc. 103 (2020) 2328–2339 [7] A. Le Coz, G. R. Durand, L. Cornet, N. Herbert, F. Gouttefangeas, L. Joanny, F. Célarié, F. Cheviré, O. Merdrignac-Conanec, First La2O2S infrared transparent ceramics, J. Eur. Ceram. Soc. 43 (2023) 2133-3142