Tunable electronic, optical, and thermal properties of trigonal XMg2N2 (X = Ca, Sr, Ba): A first-principles study

The growing demand for multifunctional materials in optoelectronic devices and thermal management systems has intensified the search for compounds that combine tunable electronic properties with controllable thermal behavior. In this context, Zintl-phase nitrides have emerged as promising candidates, yet the XMg 2 N 2 (X = Ca, Sr, Ba) family remains relatively unexplored. In this work, we present a comprehensive first-principles investigation of XMg 2 N 2 (X = Ca, Sr, Ba) compounds based on density functional theory (DFT) to evaluate their structural, mechanical, electronic, optical, and thermal properties. Structural optimization confirms that all compounds crystallize in a stable trigonal phase. The calculated elastic constants satisfy mechanical stability criteria and reveal brittle behavior along with noticeable elastic anisotropy. Electronic structure calculations using the HSE06 hybrid functional indicate that all systems are indirect semiconductors with tunable band gaps, decreasing from 3.328 eV (CaMg 2 N 2 ) to 2.936 eV (SrMg 2 N 2 ) and 1.963 eV (BaMg 2 N 2 ). Optical analysis demonstrates strong anisotropic behavior, significant absorption in the ultraviolet region, and an increasing dielectric response from Ca to Ba, highlighting their suitability for UV and optoelectronic applications. Phonon dispersion calculations confirm dynamical stability for all compounds. Furthermore, thermal properties reveal a systematic reduction in Debye temperature, melting temperature, and lattice thermal conductivity from Ca to Ba, attributed to lattice softening and enhanced anharmonicity with increasing atomic mass. Among the studied compounds, CaMg 2 N 2 exhibits superior thermal conductivity and mechanical rigidity, making it a strong candidate for thermal management applications, whereas BaMg 2 N 2 , with its lower band gap and reduced thermal conductivity, is more suitable for optoelectronic devices and thermal insulation. Overall, this study highlights the effectiveness of compositional tuning in tailoring the multifunctional properties of Zintl compounds, providing valuable insights for the design of next-generation materials for energy and optoelectronic technologies.