Abstract
Lanthanum selenidofluorides belong to wide-gap semiconductors and are promising for optoelectronics. La2F4Se, B-LaFSe compounds were obtained by the ampoule method from binary compounds. Crystals La2F4Se, R-3m, a =4.18245(11) Å, c=23.2939(6) Å, Z = 3, B-LaFSe P63/mmc, a=4.21989(5) Å, c=8.19140(10) Å, Z = 2 have a layered grain structure, their microhardnesses are 340 and 450 HV, which allows samples processing. The optical bandgap of La2F4Se is 4.5 eV. The optical bandgaps of La2F4Se and B-LaFSe were analyzed by comparing the calculated absorption spectra and the experimental Kubelka-Munk Functions. It was shown that this approach is attractive in explaining optical properties in the vicinity of fundamental absorption onset and in neighboring regions. In LaF3-La2Se3 system, temperatures and enthalpies of five phase transformations were determined, and their balance equations were obtained. It was shown that La2F4Se, B-LaFSe compounds melt incongruently and that an eutectic is formed between the phases. A phase diagram of LaF3-La2Se3 system was constructed. The liquidus calculated by Redlich-Kister polynomial agrees with the data of differential scanning calorimetry.
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