Preparation and Thermal Emission Characteristics of [Ca24Al28O64]4+:4e− Electronic Compounds

Abstract

The [Ca₂₄Al₂₈O₆₄]⁴⁺:4e⁻ electronic compounds (C12A7:e⁻) with low work function and stable chemical properties have been employed in electron emission and optical devices. In this paper, C12A7:e⁻ was successfully prepared using CaO, Al₂O₃, and Al powders through spark plasma sintering (SPS) at 1250°C for 20 min. The grain size of the sample does not exceed 10 µm. The sample exhibits typical Raman peaks at 175 cm⁻¹, 329 cm⁻¹, 510 cm⁻¹, 780 cm⁻¹, and a clear ultraviolet absorption peak at 2.6 eV. The carrier concentration of the sample reaches 1.67 × 10²¹ cm⁻³. The emission current density of the sample at 4000 V and 1100°C is 1.34 A/cm², with a fluctuation of no more than 5%. The zero-field emission current density is 1.18 A/cm² at 1100°C. The lattice thermal conductivity of C12A7:e⁻ decreases with increasing temperature, reaching 12.59 W/(K m) at 1100°C. In addition, the band structure of C12A7:e⁻ includes valence band (VB), cage conduction band (CCB), and frame conduction band (FCB), and CCB extends to the Fermi level and has a bandgap of 0.82 eV with FCB. This makes C12A7:e⁻ exhibit a typical band conduction mechanism. The electron emission characteristics of C12A7:e⁻ are derived from the contributions of the s-orbital electrons of Ca atoms and the p-orbital and d-orbital electrons of Al atoms. This article simplifies the preparation steps of C12A7:e⁻ cathode materials, shortens the synthesis cycle, and provides a foundation for the research of C12A7:e⁻ cathode.