  Recently, An electron-doped 12442-type iron-based superconductor
BaTh$_2$Fe$_4$As$_4$(N$_{0.7}$O$_{0.3}$)$_2$ has been successfully synthesized
with high-temperature solid-state reactions on basis of a structural design.
The inter-block-layer charge transfer between the constituent units of
"BaFe$_2$As$_2$" and "ThFeAsN$_{0.7}$O$_{0.3}$" was found to be essential to
stabilize the target compound. Dominant electron-type conduction and bulk
superconducting transition at ~22 K were demonstrated.
