Refining the Understanding of the Thermionic Emission Mechanism in Impregnated WBa and ScBa Cathodes Based on G.V. Samsonov’s Configurational Model II. Refined Polarization WBa-IC and ScBa-IC Thermionic Emission Model from the Standpoint of G.V. Samsonov’s Configurational Model

Abstract

The first part presented a comprehensive review of experimental studies on various types of impregnated WBa and ScBa cathodes (WBa-ICs and ScBa-ICs), used to develop thermionic emission models intended to clarify the mechanisms whereby CaO and Sc₂O₃ oxides and platinum-group metals influence cathode emission. The second part analyzes the proposed polarization WBa-IC and ScBa-IC thermionic emission model for the first time from the standpoint of G.V. Samsonov’s configurational model. The new polarization model differs from existing ones in that it incorporates donor–acceptor interactions between valence orbitals of adatoms within the emission–adsorption layer and between these adatoms and adsorbent atoms, initiated by changes in the energy stability of valence orbital configurations. According to the proposed polarization WBa-IC and ScBa-IC thermionic emission model, the electron work function is determined by the potential barriers of polarized dipole complexes of two types. These complexes result from donor–acceptor interactions between adatoms themselves and between adatoms and adsorbent atoms, Ba(Ca, Sc)⁺–O^––A⁺, and from those between adsorbed oxide molecules and adsorbent atoms, Ba⁺O^– (Ca⁺O^–)–A⁺, (Ba⁺O^––Sc^–₂O^–₃–Al⁺₂O^–₃)–A⁺, and (Ba⁺O^––Sc^–₂O^–₃–W⁺O^–₃)–A⁺. In both types, the bond between the adsorbate and the adsorbent is mediated by oxygen, acting as the electron acceptor. The characteristics of these interactions are defined by the energy stability of valence orbital configurations, d⁰, d⁵, and d¹⁰ for d-metals and s², sp³, and s²p⁶ for sp-elements, and their donor–acceptor capability. The new polarization WBa–IC and ScBa–IC thermionic emission model explains the effects of doping with CaO and Sc₂O₃ oxides and with platinum-group d-transition metals on cathode emission. Although the results are only qualitative, they are mutually consistent and correlate with emission characteristics. The simplicity of interpretation makes G.V. Samsonov’s configurational model suitable for examining charge-transfer interactions in adsorbate–adsorbent systems.