First-principles prediction of semiconducting half-Heusler KXP compounds (X: Ca, Sr, Ba) for optoelectronic and photocatalytic applications

Full-Heusler and half-Heusler compounds are extensively studied for thermoelectric applications; however, their potential in optoelectronic and photocatalytic devices remains insufficiently explored. In this study, we conducted first-principles calculations to examine the structural, electronic, optical, and photocatalytic properties of newly predicted semiconducting half-Heusler compounds KXP (where X = Ca, Sr, Ba). We confirmed structural stability through negative formation energies and mechanical stability via elastic constants that fulfill the Born-Huang criteria. Additionally, we established dynamical stability by the absence of imaginary phonon frequencies. These semi-conductors, which contain eight valence electrons, adhere to the 18-electron rule. According to HSE06 calculations, they exhibit direct band gaps of 2.37 eV for KCaP, 2.06 eV for KSrP, and 1.78 eV for KBaP, making them promising candidates for visible-light-driven applications. Our optical analysis reveals high absorption coefficients, with maximum values reaching 1.52×10[Formula: see text] cm[Formula: see text] at 5.0 eV for KCaP, 1.30×10[Formula: see text] cm[Formula: see text] at 4.90 eV for KSrP, and 1.24×10[Formula: see text] cm[Formula: see text] at 4.62 eV for KBaP, indicating strong light-matter interactions. Furthermore, an analysis of band edge alignment shows that the valence and conduction band positions correlate with the redox potentials for water splitting, facilitating both oxygen evolution and hydrogen evolution reactions. The strong hybridization between X[Formula: see text] and P[Formula: see text] orbitals enhances charge carrier separation and mobility, thereby reducing recombination losses, which is vital for efficient photocatalysis. Given their thermodynamic and mechanical robustness, KXP half-Heusler compounds present an exciting opportunity for applications in optoelectronic devices and photocatalytic water splitting.