Phase transitions in double molybdates K2M2II(MoO4)3 with M = Mg or Co

Phase transitions and cation mobility in double molybdates K2M2II (MoO4)(3) with M = Mg or Co and the products of their heterovalent doping with scandium(III) and vanadium(V) have been studied. The transition from low to high conductivity in K2MII MoO4)(3) is the result of a two-stage phase transition, whose occurrence is significantly extended in time. Heterovalent substitutions noticeably decrease the heat of the phase transition. The transition to the low-temperature phase is not achieved even after long-term exposure.