The new compounds Yb2M(I)3Fe5O12 (M(I) - Li, Na, K) have been synthesized by solid phase method from oxides of lithium, sodium, potassium, iron and lanthanum. By means of XRD analysis it was determined that the compounds crystallize in a tetragonal crystal system.
The compounds' heat capacities have been measured in the range of temperature 298.15... 673 K and have been found lambda- shaped jumps on the dependence diagrams C-P(o)similar to f (T) which caused, probably by phase transitions of the second type.