Enhanced thermoelectric performance in Ca1-xEuxZn2Sb2 Zintl phases via compositional tuning

The thermoelectric performance of the Zintl phase series Ca 1-x Eu x Zn 2 Sb 2 ( x = 0, 0.25, 0.5, 0.75, 1) is investigated via first-principles calculations. Our analysis reveals that compositional tuning directly controls the charge and heat transport. Increasing the Eu concentration ( x ) enhances electrical conductivity through raised hole concentration, but at the cost of a reduced Seebeck coefficient. Crucially, the lattice thermal conductivity (κ L ) is minimized to approximately 1.3 W/m·K at room temperature for the solid solutions (0 < x < 1), a reduction of nearly 50% compared to the parent compounds, due to effective alloy scattering of phonons. This results in the desired phonon-glass, electron-crystal character. The calculated electronic transport coefficients and the suppressed κ L show excellent agreement with experimental data, validating our computational approach. The optimal p -type performance is achieved for Ca 0.75 Eu 0.25 Zn 2 Sb 2 , which reaches a figure of merit ZT of ∼0.7 at 800 K. Furthermore, theoretical mapping of the transport properties identifies an even higher potential for n -type doping, with a predicted maximum ZT of 0.86. This study not only identifies a high-performance composition but also establishes a foundational strategy for optimizing thermoelectric Zintl phases.