Structural, electronic, and optical properties of three types Ca₃N₂ from first-principles study

Context: To find the potential value of Ca₃N₂ in the field of optoelectronics, the physical properties of Ca₃N₂ will be analyzed. It can be concluded from the electronic properties that the Ca-N bonds of α-Ca₃N₂ are more stable than those of δ-Ca₃N₂ and ε-Ca₃N₂. The dielectric function, reflectivity function, and absorption function of three types of Ca₃N₂ were accurately calculated, and it was concluded that α-Ca₃N₂, δ-Ca3N₂, and ε-Ca₃N₂ have greater transmittance for visible light and exhibit optical transparency in the near-infrared frequency domain. Combined with the high hardness, strong bonding, high melting point, and wear resistance of Ca₃N₂, Ca3N₂ can be used as a new generation of window heat-resistant materials. The α-Ca₃N₂, δ-Ca₃N₂, and ε-Ca₃N₂ are indirect, direct, and indirect narrow bandgap compounds, respectively, that is, δ-Ca₃N₂ is more suitable for luminescent materials than α-Ca₃N₂ and ε-Ca₃N₂. α-Ca₃N₂ and δ-Ca₃N₂ have high reflective properties in the ultraviolet region and can be used as UV protective coatings. All three Ca₃N₂ materials can be used industrially to synthesize photovoltaic devices that operate in the ultraviolet region. Methods: Based on the first-principles of density functional theory calculations, the structures, electronic properties, and optical properties of α-_Ca3N2, δ-Ca₃N₂, and ε-Ca₃N₂ were calculated. The calculation results show that although the α-Ca₃N₂, δ-Ca₃N₂, and ε-Ca₃N₂ have similar electronic structures, some phases have better properties in some aspects.