Calcium lanthanum sulfide (CLS) has been identified as a candidate material for various optical applications due to its wide transmission range, high refractive index, desirable thermo-optic properties, and refractory behavior. Implementation of CLS in optical systems has remained unrealized due to various difficulties in the synthesis and bulk fabrication of this material. The key challenge facing the development of CLS is the incorporation of oxygen and the presence of unwanted secondary phases related to the lack of control of stoichiometric variations across the ternary phase diagram. Though these difficulties have been previously discussed in the processing of CLS, the exact form, mechanisms of formation and impact of these attributes have not been systematically evaluated. Each of these problems must be meticulously elaborated upon to understand what processing conditions are needed to avoid these common pitfalls which have been shown to degrade the ultimate optical quality of the resulting ceramic. This thesis investigated the role of oxygen in CLS ceramics as it applies to the resulting optical quality of the processed ceramic. The research done specifically examined ceramic materials with high La- content, prepared by hot pressing and hot isostatic pressing. The materials chosen for this work displayed varying levels of optical quality and phase purity. Determination of the desired cubic crystal structure as the main phase present was confirmed using x-ray diffraction and transmission electron microscopy. Through the correlation of data from multiple material metrology tools, the concentration and bond environment of oxygen in the ceramics and starting powders has been determined. It has been shown that the role of oxygen does not necessarily induce local phase transformation in the crystalline material, but rather can be dissolved into the CLS crystal lattice in low levels. Raman spectroscopy has been identified as a simple, useful tool that can be used to aid future synthesis routes due to its ability to differentiate the different types of O present. This thesis demonstrates how low levels of oxygen impurities can be incorporated into the CLS lattice utilizing simple IR and Raman spectroscopy techniques.
| Identifer | oai:union.ndltd.org:ucf.edu/oai:stars.library.ucf.edu:etd2023-1109 |
| Date | 01 January 2023 |
| Creators | Kostogiannes, Alexandros |
| Publisher | STARS |
| Source Sets | University of Central Florida |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Graduate Thesis and Dissertation 2023-2024 |
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