Thermionic Emission of Yttrium Dodecaboride Single Crystal

Abstract:

Experimental data on thermionic current density and electron work function of YB₁₂ (100) at T = 1218 – 1978 K in high vacuum (p < 10^-4 Pa) are first introduced. Temperature dependences of the thermionic current density and effective electron work function are presented without extrapolation to the zero-field currents because of the anomalous Schottky effect. The temperature dependences of theYB₁₂ electron work function can be described by linear functions at certain temperature intervals. Preferential boron evaporation and additional ion bombardment by the residual gases ions and evaporated boron ions results in appearance of new phases depleted of boron on the YB₁₂ surface. As a result, an YB₄ – YB₆ double layer on the YB₁₂ single crystal surface has formed. The appearance of the new boride phases, depleted of boron, on the emitting surface causes an increase of thermionic current density compared with individual YB₁₂.

• Periodical: Solid State Phenomena (Volume 289)
• Pages: 47-52
• DOI: https://doi.org/10.4028/www.scientific.net/SSP.289.47
• Online since: April 2019
• Authors: Daniil Voronovych*, Anatoliy Taran, Oksana Podshyvalova, Natalya Shitsevalova, Volodymyr Filipov, Anatoliy Dukhnenko
• Keywords: Dodecaboride, Hexaboride, Single Crystal, Tetraboride, Thermionic Properties

References

[1] J. Etourneau, Critical survey of rare-earth borides: Occurrence, crystal chemistry and physical properties, J. Less-Common Met. 110 (1985) 267 – 281.

DOI: 10.1016/0022-5088(85)90333-9

[2] T. Tanaka, S. Okada, Y. Yu, Y. Ishizawa, A New Yttrium Boride: YB25, J. Solid State Chem. 133 (1997) 122 – 124.

DOI: 10.1006/jssc.1997.7328

[3] T. Tanaka, S. Okada, Y. Ishizawa, A new yttrium higher boride: YB50. J. Alloy. Compd., 205 (1994) 281 – 284.

DOI: 10.1016/0925-8388(94)90802-8

[4] T.B. Massalski (Editor-in-Chief), Binary Alloy Phase Diagrams, 2nd Ed. plus updates, ASM International, ASM CD-ROM, Ohio, USA (1996).

[5] A. Taran, D. Voronovich, N. Shitsevalova, A. Levchenko, V. Filipov, S. Abashin, Phase transformations in lutetium borides at heating in vacuum, Solid State Phenom. 464 (2011) 172 – 174.

DOI: 10.4028/www.scientific.net/ssp.172-174.464

[6] D. Voronovich, A. Taran, N. Shitsevalova, A. Levchenko, V. Filipov, Anisotropy of the erbium dodecaboride thermionic properties, Solid State Sci. 14 (2012) 1624 – 1628.

DOI: 10.1016/j.solidstatesciences.2012.04.009

[7] D. Voronovich, A. Taran, N. Shitsevalova, A. Levchenko, V. Filipov, Thermal instability of holmium and thulium dodecaborides in vacuum, Solid State Phenom. 257 (2017) 152 – 155.

DOI: 10.4028/www.scientific.net/ssp.257.152

[8] G. A. Meerson, N. N. Zhuravlev, R. M. Manelis, A. D. Runov, A. A. Stepanova, L. N. Grishina, N. V. Gramm, Some properties of yttrium borides, Izv. Akad. Nauk SSSR, Neorgan. Materialy 2 (1966) 608 – 616 [in Russian].

[9] G. V. Samsonov, L. N. Okhremchuk, I. A. Podchenyaeva, V. S. Fomenko, V. V. Odintsov, Thermoemission of transition metal dodecaborides, Izv. Akad. Nauk SSSR, Neorgan. Materialy 10 (1974) 270 – 272 [in Russian].

[10] J. Jaskie, D. Jacobson, Thermionic emission and surface composition of the Y – B system, J. Energy 5 (1981) 187 – 189.

DOI: 10.2514/3.62524

[11] A. Czopnik, N. Shitsevalova, V. Pluzhnikov, A. Krivchikov, Yu. Paderno, Y. Onuki, Low temperature thermal properties of yttrium and lutetium dodecaborides. J. Phys.: Condens. Matter 17 (2005) 5971 – 5985.

DOI: 10.1088/0953-8984/17/38/003

[12] L.N. Dobretsov, M.V. Gomoyunova, Emission Electronics, Israel Program for Scientific Translations, Jerusalem, 1971, 433 p.

[13] K. Takahashi, S. Kunii, Single crystal growth and properties of incongruently melting TbB6, DyB6, HoB6, and YB6, J. Solid State Chem. 133 (1997) 198 – 200.

DOI: 10.1006/jssc.1997.7427