Stability and properties of the friendly environmental Zintl phases: Ca3Si4 and Ca14Si19

Abstract We report the synthesis, stability, lattice dynamics and electronic properties of two Zintl phases, Ca 3 Si 4 and Ca 14 Si 19 , made of abundant and non-toxic elements in order to evaluate their potential applications. A simple two-step synthesis approach has permitted (i) to reach good purity of these two silicide phases and (ii) to reinvestigate their coexistence domain which permits to lift the uncertainty of the phase diagram within the 50–70 at. % Si region. Our first-principles calculations are able to well describe for the first time both the experimental vibrational properties studied by Raman spectroscopy and the energy bandgap determined by diffuse reflectance experiments. The two compounds are narrow-gap intrinsic semiconductors with indirect energy bandgaps about 0.56 eV and smaller than 0.1 eV for Ca 3 Si 4 and Ca 14 Si 19 , respectively. Their Seebeck coefficient has been measured to 42 μV/K (Ca 3 Si 4 ) and −183 μV/K (Ca 14 Si 19 ) at room temperature which suggests their p - and n -type semiconducting behavior, respectively.