The thermal decomposition of ammonium thiocyanate (NH 4 SCN) was studied by thermogravimetry, differential thermal analysis, and mass spectrometry. It occurred in the temperature range from 400 to 530 K. The decomposition products contained NH 3 , CS 2 , H 2 S, and HNCS gases. Rare-earth oxides were reacted with these gases at 1273 K for 8 h in order to prepare rare-earth sulfides. The single tetragonal -La 2 S 3 phase was formed after the sulfurization of La 2 O 3 . In contrast, the single orthorhombic -Gd 2 S 3 phase was formed after the sulfurization of Gd 2 O 3 . These powders were consolidated by pressure-assisted sintering to fabricate the thermoelectric elements.
We have studied phase formation processes in the La-O-S system during La 2 O 3 sulfurization in ammonium rhodanide vapor and identified the sequence of steps in lanthanum oxide conversion into oxysul fides and lanthanum sulfide using X ray diffraction, IR absorption spectroscopy, and Raman spectroscopy. In the initial stage of the sulfurization process, we observed the formation of lanthanum dioxydisulfide, which converted into lanthanum dioxymonosulfide and lanthanum sesquisulfide during further sulfurization. Our results demonstrate that low structural perfection of lanthanum oxide allows reactive sulfur to penetrate the surface layer, which probably favors lanthanum dioxydisulfide formation.
The mechanisms of pyrolysis in He and reduction in H 2 of a Ni(ktfaa) 2 chelate and nickel film deposition on copper substrates are discussed. The Ni films produced by CVD with the Ni(ktfaa) 2 chelate as a precursor are continuous. Pyrolysis of the Ni(ktfaa) 2 chelate takes place above 300 C. The hydrogen atmosphere allows the reaction temperature to be decreased to 213 C, but the film deposition rate is low. 300 C is the optimal temperature for continuous Ni film deposition on Cu substrates. The mechanism of hydrogen interaction with the adsorbed Ni(ktfaa) 2 chelate is discussed.
The heat capacity Cp, thermal diffusivity χT, and lattice thermal conductivity κlatt of ceramic solid solutions of sesquisulfides Gd3‐xVGd,xS4 (0 < x < 0.33) in the temperature range 300‐700 K has been studied. Changing the real structure, namely the concentrations of vacancies (NV) and deformation (NDc) centers of polycrystals, significantly decreases κlatt. A deviation of composition from the stoichiometry 2:3 is accompanied by an increase in the specific area of the crystallite boundaries per unit volume, and, hence, the concentration of deformation centers DC increases. This observation was confirmed by examining the short‐range order disturbance of the lattice and symmetry environment of the Gd3+ and S2− environment by Raman spectroscopy and the magnetic susceptibility Faraday method. Therefore the thermal diffusivity of gadolinium sesquisulfide is reduced because of the mean free path of phonons decrease. As a result, the thermal conductivity of the polycrystalline samples is reduced by 10%.
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