Voronovych D. Thermionic and emissive properties of rare-earth metals dodecaborides single crystals

Thesis is devoted to experimental research and modeling of the thermionic and radiative properties of the holmium, erbium, thulium, lutetium dodecaborides, the lutetium tetra- and diboride single crystals and determination of correlation of structure and composition of the single crystals with these properties at high temperatures. The experimental results of phase transformations research of the investigated rare-earth metals borides single crystals at their heating in a vacuum to the high temperatures are presented. It is shown that the phase transformation in the surface layers of rare-earth metals dodecaborides single crystals with formation of rare earth metals tetraborides takes place at their heating in a vacuum at Т > 1200 К. Lutetium diboride appears not only in surface layer of lutetium tetraboride single crystal but in its bulk with formation of oriented lutetium diboride lamels. It is shown that thermionic and radiative properties of the investigated rare-earth metals borides single crystals are determined by a structure and composition of the surface layers of these single crystals. Keywords: single crystal, rare-earth metal dodecaboride, thermionic emission, spectral emissivity, electron work function.