Properties of La2F4Se, B–LaFSe phases. Phase diagram of the LaF3–La2Se3 system

https://doi.org/10.1016/j.jssc.2024.124880

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.