  By tackling the challenge of extending transparent oxide semiconductors to Ge
based oxides, we have found a not-yet-reported crystal structure, named
$\beta$-SrGe$_2$O$_5$, which is composed of edge-sharing GeO$_6$ octahedra
interconnected by GeO$_5$ bipyramids. Single crystals were successfully grown
by the high-pressure flux method. $\beta$-SrGe$_2$O$_5$ has a band gap of 5.2
eV and a dispersive conduction band with an effective mass as small as 0.34
times the electron rest mass, which originates from the edge-sharing GeO$_6$
octahedra network. Although known compounds with octahedral GeO$_6$
coordination are commonly unstable at atmospheric pressure and elevated
temperatures, $\beta$-SrGe$_2$O$_5$ exhibits thermal stability up to 700
$^\circ$C.
