Intermetallic compounds obtained from $Me_3$Ge$_2$O$_5$(OH)$_4$ ($Me$ = Mg, Ni, Fe, Co) phyllogermanates: synthesis of single-phase precursors

Typically, intermetallic compounds are prepared by solid-state method at high temperatures. We propose a simple method to obtain intermetallic compounds by reduction in Ar–H$_2$ atmosphere from precursors. In particular, Co$^{2+}$ and Fe$^{2+}$ oxidation in hydrothermal conditions grants additional experimental challenge. Here, we report successful Fe phyllogermanate synthesis for the first time. We identify general patterns of formation and determine the effect of hydrothermal treatment on phase composition and morphology for the whole series of phyllogermanates. Formation of phyllogermanates under hydrothermal conditions is studied in the 100 – 200$^\circ$C temperature range in three hydrothermal media: H$_2$O, NaOH, Na$_2$SO$_3$. The latter inhibits the oxidation of Co$^{2+}$ and Fe$^{2+}$ during the synthesis. An increase in temperature favors to the formation of phase described by three-layers unit cell. Heat treatment in an Ar–H$_2$ atmosphere allows us to obtain intermetallic compounds and $Me_x$Ge$_y$ alloys, and to establish the temperature regimes of the reduction processes.