The electronic properties of the Ca/Sr and Mn site substitution of ${\mathrm{CaMnGe}}_2{\mathrm{O}}_6$ and ${\mathrm{SrMnGe}}_2{\mathrm{O}}_6$ clinopyroxene systems have been investigated by ab initio calculations within the density functional theory (DFT) framework, using on-site Hubbard $U$ to describe the highly correlated Mn $3d$ states and a hybrid exchange-correlation functional to obtain the energy band-gap values. Compositions such as ${(\mathrm{Ca},\mathrm{Sr})}_{1-x}{\mathrm{Cd}}_x{\mathrm{MnGe}}_2{\mathrm{O}}_6$ and $(\mathrm{Ca},\mathrm{Sr}){\mathrm{Mn}}_{1-x}{\mathrm{Cd}}_x{\mathrm{Ge}}_2{\mathrm{O}}_6$ (where $x=0.125,0.25$) are predicted to be stable. Also, we proved that implanted Cd impurity could indeed replace either the Ca/Sr or the Mn sites in the crystalline structures. These findings were obtained by combining first principles electric field gradient calculations, using a supercell scheme, with experimental time-differential perturbed angular correlation results. Additionally, DFT calculations showed that Cd substitution is expected to lead to a reduction in the band-gap width. Cd-doped systems were successfully synthesized and experimental results evidencing opportunities for potential band-gap engineering are reported.

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• Density of states
• Ferroelectricity
• Fine & hyperfine structure
• Ab initio calculations
• Perturbed-angular correlation spectroscopy