New materials with potential for optical device applications: The synthesis and characterization of new mixed-metal quaternary sulfides and selenides

[摘要] The search for new materials with desirable optical properties has become important in recent years. In particular, a need has emerged for compounds that are candidates for use as long-wavelength (8-12 $mu$m) infrared window materials. At the present time there is a deficiency of suitable materials which are appropriate for use in the long-wavelength infrared region. This is because there is an inherent conflict (the chemical characteristics that give the best structural and mechanical properties also tend to degrade the optical properties), which needs to be overcome in the search for advanced optical window materials. I have investigated the exploratory synthesis of new mixed-metal chalcogenides, particularly sulfide and selenide compounds, that might display potential for such applications. Our strategy in designing new compounds was to incorporate heavy metals, which display low or intermediate cation coordination, into three-dimensional chalcogenide crystal structures. We felt that the three-dimensional chalcogenide framework would fulfill the structural requirements necessary to retain satisfactory mechanical properties and chemical inertness while allowing the compound to also possess good optical properties. My work entailed the high-temperature (600$spcirc$C $sim$ 1200$spcirc$C) solid-state synthesis of new mixed-metal quaternary chalcogenide compounds with a general formula A$sb{m x}$(RE)$sb{m y}$M$sb{m z}$Q$sb{m p}$, where A = Ca or Ba; RE = La-Yb; M = In; and Q = S or Se. Various synthetic techniques, other than conventional high-temperature solid-state methods, have been employed to grow single crystals for physical property measurements; namely vapor transport and molten salt methods. To characterize these new materials, we used a variety of analytical techniques including both single crystal and powder X-ray diffraction techniques, Weissenberg X-ray film techniques, thermal analysis (TGA and DTA), and optical spectroscopy. Preliminary results from DRIFTS (diffuse reflectance infrared fourier transform spectroscopy), single crystal transmittance and UV/VIS reflectance spectroscopy, as well as thermal analysis, suggest that these new compounds may have potential for use in advanced optical devices that are subjected to extreme conditions.

[发布机构] Rice University